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Default Using a photoresistor and light to turn a transistor OFF...

As per my post in SEB, I am trying to use a photo resistor and sunlight to
turn off a transistor that would otherwise be conducting like crazy, but
can't quite make the leap of comprehension as to how to actually do this.
Please see attached schematic parts that show more or less what I am trying
to do this with. No part number for the photoresistor, sorry. It drops
from multi-megohms in the dark to single-digit Ohms in the light and seems
perfectly capable of carrying the 30 to 50 mA current I am working with at
the voltages indicated. Would really appreciate it if someone could offer a
hint as to how I should proceed with as few components as possible (small
circuit board.) I hope that my method of posting the schematic portion of
what I a working with is not too obtuse. Couldn't figure out any other way
to do it...

Many thanks...

Dave





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Default Using a photoresistor and light to turn a transistor OFF...

On 10/07/2011 06:36 AM, Dave wrote:
As per my post in SEB, I am trying to use a photo resistor and sunlight to
turn off a transistor that would otherwise be conducting like crazy, but
can't quite make the leap of comprehension as to how to actually do this.
Please see attached schematic parts that show more or less what I am trying
to do this with. No part number for the photoresistor, sorry. It drops
from multi-megohms in the dark to single-digit Ohms in the light and seems
perfectly capable of carrying the 30 to 50 mA current I am working with at
the voltages indicated. Would really appreciate it if someone could offer a
hint as to how I should proceed with as few components as possible (small
circuit board.) I hope that my method of posting the schematic portion of
what I a working with is not too obtuse. Couldn't figure out any other way
to do it...

Many thanks...

Dave




You're wasting a gross amount of current in that bias network. How
about a nice MOSFET?

Say a 2N7002, source to V-, drain to series resistor+LED, LDR plus pot
to set turn-on level:

(V+)----*----------------*
| |
| R
| R
| R
| R
*---* |
| | ---
| R \ / -----
*- R ----- -----
R |
R | | D
| | |---*
| | |--; 2N7000
*----------J |---*
| | | S
| |
L |
D |
R |
| |
| |
(V-)----*----------------*














--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net
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Default Using a photoresistor and light to turn a transistor OFF...

"Phil Hobbs" wrote in message
...
On 10/07/2011 06:36 AM, Dave wrote:
As per my post in SEB, I am trying to use a photo resistor and sunlight
to
turn off a transistor that would otherwise be conducting like crazy, but
can't quite make the leap of comprehension as to how to actually do this.
Please see attached schematic parts that show more or less what I am
trying
to do this with. No part number for the photoresistor, sorry. It drops
from multi-megohms in the dark to single-digit Ohms in the light and
seems
perfectly capable of carrying the 30 to 50 mA current I am working with
at
the voltages indicated. Would really appreciate it if someone could
offer a
hint as to how I should proceed with as few components as possible (small
circuit board.) I hope that my method of posting the schematic portion
of
what I a working with is not too obtuse. Couldn't figure out any other
way
to do it...

Many thanks...

Dave




You're wasting a gross amount of current in that bias network. How about
a nice MOSFET?

Say a 2N7002, source to V-, drain to series resistor+LED, LDR plus pot to
set turn-on level:

(V+)----*----------------*
| |
| R
| R
| R
| R
*---* |
| | ---
| R \ / -----
*- R ----- -----
R |
R | | D
| | |---*
| | |--; 2N7000
*----------J |---*
| | | S
| |
L |
D |
R |
| |
| |
(V-)----*----------------*














--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net


Oh, man. Something to WORK with. THANK YOU! Much appreciated...

Dave


http://electrooptical.net



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Default Using a photoresistor and light to turn a transistor OFF...

On 10/07/2011 07:13 AM, Dave wrote:
"Phil wrote in message
...
On 10/07/2011 06:36 AM, Dave wrote:
As per my post in SEB, I am trying to use a photo resistor and sunlight
to
turn off a transistor that would otherwise be conducting like crazy, but
can't quite make the leap of comprehension as to how to actually do this.
Please see attached schematic parts that show more or less what I am
trying
to do this with. No part number for the photoresistor, sorry. It drops
from multi-megohms in the dark to single-digit Ohms in the light and
seems
perfectly capable of carrying the 30 to 50 mA current I am working with
at
the voltages indicated. Would really appreciate it if someone could
offer a
hint as to how I should proceed with as few components as possible (small
circuit board.) I hope that my method of posting the schematic portion
of
what I a working with is not too obtuse. Couldn't figure out any other
way
to do it...

Many thanks...

Dave




You're wasting a gross amount of current in that bias network. How about
a nice MOSFET?

Say a 2N7002, source to V-, drain to series resistor+LED, LDR plus pot to
set turn-on level:

(V+)----*----------------*
| |
| R
| R
| R
| R
*---* |
| | ---
| R \ / -----
*- R ----- -----
R |
R | | D
| | |---*
| | |--; 2N7000
*----------J |---*
| | | S
| |
L |
D |
R |
| |
| |
(V-)----*----------------*





Oh, man. Something to WORK with. THANK YOU! Much appreciated...

Dave



De nada. If you're planning to use that circuit for real, you might
want an 0.1 uF cap from gate to source. That'll make it less twitchy
and less vulnerable to electrostatic discharge.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net
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Default Using a photoresistor and light to turn a transistor OFF...


"Phil Hobbs" wrote in message
...
On 10/07/2011 07:13 AM, Dave wrote:
"Phil wrote in message
...
On 10/07/2011 06:36 AM, Dave wrote:
As per my post in SEB, I am trying to use a photo resistor and sunlight
to
turn off a transistor that would otherwise be conducting like crazy,
but
can't quite make the leap of comprehension as to how to actually do
this.
Please see attached schematic parts that show more or less what I am
trying
to do this with. No part number for the photoresistor, sorry. It
drops
from multi-megohms in the dark to single-digit Ohms in the light and
seems
perfectly capable of carrying the 30 to 50 mA current I am working with
at
the voltages indicated. Would really appreciate it if someone could
offer a
hint as to how I should proceed with as few components as possible
(small
circuit board.) I hope that my method of posting the schematic portion
of
what I a working with is not too obtuse. Couldn't figure out any other
way
to do it...

Many thanks...

Dave




You're wasting a gross amount of current in that bias network. How
about
a nice MOSFET?

Say a 2N7002, source to V-, drain to series resistor+LED, LDR plus pot
to
set turn-on level:

(V+)----*----------------*
| |
| R
| R
| R
| R
*---* |
| | ---
| R \ / -----
*- R ----- -----
R |
R | | D
| | |---*
| | |--; 2N7000
*----------J |---*
| | | S
| |
L |
D |
R |
| |
| |
(V-)----*----------------*





Oh, man. Something to WORK with. THANK YOU! Much appreciated...

Dave



De nada. If you're planning to use that circuit for real, you might
want an 0.1 uF cap from gate to source. That'll make it less twitchy and
less vulnerable to electrostatic discharge.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net


Gotcha. Thanks again.

D




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Default Using a photoresistor and light to turn a transistor OFF...

On Fri, 07 Oct 2011 07:26:02 -0400, Phil Hobbs
wrote:

On 10/07/2011 07:13 AM, Dave wrote:
"Phil wrote in message
...
On 10/07/2011 06:36 AM, Dave wrote:
As per my post in SEB, I am trying to use a photo resistor and sunlight
to
turn off a transistor that would otherwise be conducting like crazy, but
can't quite make the leap of comprehension as to how to actually do this.
Please see attached schematic parts that show more or less what I am
trying
to do this with. No part number for the photoresistor, sorry. It drops
from multi-megohms in the dark to single-digit Ohms in the light and
seems
perfectly capable of carrying the 30 to 50 mA current I am working with
at
the voltages indicated. Would really appreciate it if someone could
offer a
hint as to how I should proceed with as few components as possible (small
circuit board.) I hope that my method of posting the schematic portion
of
what I a working with is not too obtuse. Couldn't figure out any other
way
to do it...

Many thanks...

Dave




You're wasting a gross amount of current in that bias network. How about
a nice MOSFET?

Say a 2N7002, source to V-, drain to series resistor+LED, LDR plus pot to
set turn-on level:

(V+)----*----------------*
| |
| R
| R
| R
| R
*---* |
| | ---
| R \ / -----
*- R ----- -----
R |
R | | D
| | |---*
| | |--; 2N7000
*----------J |---*
| | | S
| |
L |
D |
R |
| |
| |
(V-)----*----------------*





Oh, man. Something to WORK with. THANK YOU! Much appreciated...

Dave



De nada. If you're planning to use that circuit for real, you might
want an 0.1 uF cap from gate to source. That'll make it less twitchy
and less vulnerable to electrostatic discharge.



Phil has already answered the hard part but for the posting schematics
part, try either AACircuit or LTSpice.

AACircuit is available over at http://www.tech-chat.de/aacircuit.html
A rendering of your right-hand snippet would look like (view with a
fixed-pitch font):

2N3904
V- o-------o--------- ----------.
| ^ / |
| --- |
| | .-.
.-. | | |
| | | | | 160
120 | | | '-'
'-' | |
| | |
| | |
o----------' |
| |
| |
| |
.-. -
| | ^ -
680 | | |
'-' | NTE 30045
| |
| |
V+ o-------o----------------------'
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

Stylized but understandable -- and easier than trying to do it in a text
editor or Usenet client's window.


LTSpice is one of several free apps provided by Linear Technology
http://www.linear.com/designtools/software/ It is a full Spice
simulator but it's also used around here to pass the schematics as ASCII
netlists.

AACircuit is typically best for small snippets, and nice since they are
directly viewable. LTSpice for the larger layouts.

Version 4
SHEET 1 880 680
WIRE 128 -32 -16 -32
WIRE 208 -32 128 -32
WIRE 384 -32 304 -32
WIRE 128 48 128 -32
WIRE 384 48 384 -32
WIRE 128 160 128 128
WIRE 256 160 256 32
WIRE 256 160 128 160
WIRE 128 192 128 160
WIRE 384 208 384 128
WIRE 128 336 128 272
WIRE 128 336 -16 336
WIRE 384 336 384 272
WIRE 384 336 128 336
SYMBOL res 112 32 R0
SYMATTR InstName R1
SYMATTR Value 120
SYMBOL res 112 176 R0
SYMATTR InstName R2
SYMATTR Value 680
SYMBOL res 368 32 R0
SYMATTR InstName R3
SYMATTR Value 160
SYMBOL npn 304 32 M270
SYMATTR InstName Q1
SYMATTR Value 2N3904
SYMBOL LED 400 272 R180
WINDOW 0 24 64 Left 2
WINDOW 3 24 0 Left 2
SYMATTR InstName D1
TEXT -56 -32 Left 2 ;V-
TEXT -64 336 Left 2 ;V+

--
Rich Webb Norfolk, VA
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Default Using a photoresistor and light to turn a transistor OFF...

On Fri, 07 Oct 2011 06:59:06 -0400, Phil Hobbs wrote:

On 10/07/2011 06:36 AM, Dave wrote:
As per my post in SEB, I am trying to use a photo resistor and sunlight
to turn off a transistor that would otherwise be conducting like crazy,
but can't quite make the leap of comprehension as to how to actually do
this. Please see attached schematic parts that show more or less what I
am trying to do this with. No part number for the photoresistor,
sorry. It drops from multi-megohms in the dark to single-digit Ohms in
the light and seems perfectly capable of carrying the 30 to 50 mA
current I am working with at the voltages indicated. Would really
appreciate it if someone could offer a hint as to how I should proceed
with as few components as possible (small circuit board.) I hope that
my method of posting the schematic portion of what I a working with is
not too obtuse. Couldn't figure out any other way to do it...

Many thanks...

Dave




You're wasting a gross amount of current in that bias network. How
about a nice MOSFET?

Say a 2N7002, source to V-, drain to series resistor+LED, LDR plus pot
to set turn-on level:

(V+)----*----------------*
| |
| R
| R
| R
| R
*---* |
| | ---
| R \ / -----
*- R ----- -----
R |
R | | D
| | |---*
| | |--; 2N7000
*----------J |---*
| | | S
| |
L |
D |
R |
| |
| |
(V-)----*----------------*


I couldn't find the original post, but if you're driving 20mA to an LED
you should only need a mA (at most!) into the base of a BJT. So you
could almost use Dr Hobbs's circuit above with an NPN, or use something
like



V+ o----------------o------------.
| |
| |
.-. .-.
| | R2 | | R5
| | | |
'-' '-'
| |
| |
.---------o |
| | |
| | V -
| .-. -
| | | R3 | D1
| | | |
| '-' |
| | |
| | |/
| o----------| Q1
| | |
| | |
.-. .-. |
~ | | R1 | | R4 |
~ | | | | |
'-' '-' |
| | |
| | |
| | |
V- o -----o---------o------------'
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

Set up R2 and R3 to bias the transistor on, with R4 to lend a bit of
authority pulling the base down. When R1 starts to conduct the junction
of R2 and R3 doesn't have to get all the way down to 0.6V in order to
turn Q1 off fully.

Come to think of it, you could do this all with a jelly-bean comparator,
and add some hysteresis to boot. Then D1 would snap on and off, instead
of shivering on and shivering off as the light changes.

--
www.wescottdesign.com
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Default Using a photoresistor and light to turn a transistor OFF...


"Dave" wrote in message
...
As per my post in SEB, I am trying to use a photo resistor and sunlight to
turn off a transistor that would otherwise be conducting like crazy, but
can't quite make the leap of comprehension as to how to actually do this.
Please see attached schematic parts that show more or less what I am
trying to do this with. No part number for the photoresistor, sorry. It
drops from multi-megohms in the dark to single-digit Ohms in the light and
seems perfectly capable of carrying the 30 to 50 mA current I am working
with at the voltages indicated. Would really appreciate it if someone
could offer a hint as to how I should proceed with as few components as
possible (small circuit board.) I hope that my method of posting the
schematic portion of what I a working with is not too obtuse. Couldn't
figure out any other way to do it...

Many thanks...



There were several projects in the Philips EE kits based on a 2 transistor
schmidt-trigger that produced a nice snap on/off with an ORP12 LDR.

Haven't looked recently but there was some guy in the Nederlands running a
Philips EE website with a collection of handbooks in various languages,
between the schematics in the handbooks and the circuit overlay cards
there's ample examples of a simple circuit that will do the job.


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Default Using a photoresistor and light to turn a transistor OFF...


"Dave" wrote in message
...
As per my post in SEB, I am trying to use a photo resistor and sunlight to
turn off a transistor that would otherwise be conducting like crazy, but
can't quite make the leap of comprehension as to how to actually do this.
Please see attached schematic parts that show more or less what I am
trying to do this with. No part number for the photoresistor, sorry. It
drops from multi-megohms in the dark to single-digit Ohms in the light and
seems perfectly capable of carrying the 30 to 50 mA current I am working
with at the voltages indicated. Would really appreciate it if someone
could offer a hint as to how I should proceed with as few components as
possible (small circuit board.) I hope that my method of posting the
schematic portion of what I a working with is not too obtuse. Couldn't
figure out any other way to do it...

Many thanks...

Dave


Some 2-transistor LDR switches among this lot:

http://ee.old.no/library/


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Default Using a photoresistor and light to turn a transistor OFF...


"Dave" schreef in bericht
...
As per my post in SEB, I am trying to use a photo resistor and sunlight to
turn off a transistor that would otherwise be conducting like crazy, but
can't quite make the leap of comprehension as to how to actually do this.
Please see attached schematic parts that show more or less what I am
trying to do this with. No part number for the photoresistor, sorry. It
drops from multi-megohms in the dark to single-digit Ohms in the light and
seems perfectly capable of carrying the 30 to 50 mA current I am working
with at the voltages indicated. Would really appreciate it if someone
could offer a hint as to how I should proceed with as few components as
possible (small circuit board.) I hope that my method of posting the
schematic portion of what I a working with is not too obtuse. Couldn't
figure out any other way to do it...

Many thanks...

Dave


Why use a photo resistor while you have a solar cell at hand? Increase the
120/680 voltage divider to at least 1k2/6k8 and place it across the solar
cell. You may need to change one of them to find the right switching point
(though it's more a traject the a point) or use a 10k/lin potmeter for
experimenting.

petrus bitbyter




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Default Using a photoresistor and light to turn a transistor OFF...

On Fri, 07 Oct 2011 07:26:02 -0400, Phil Hobbs
wrote:

On 10/07/2011 07:13 AM, Dave wrote:
"Phil wrote in message
...
On 10/07/2011 06:36 AM, Dave wrote:
As per my post in SEB, I am trying to use a photo resistor and sunlight
to
turn off a transistor that would otherwise be conducting like crazy, but
can't quite make the leap of comprehension as to how to actually do this.
Please see attached schematic parts that show more or less what I am
trying
to do this with. No part number for the photoresistor, sorry. It drops
from multi-megohms in the dark to single-digit Ohms in the light and
seems
perfectly capable of carrying the 30 to 50 mA current I am working with
at
the voltages indicated. Would really appreciate it if someone could
offer a
hint as to how I should proceed with as few components as possible (small
circuit board.) I hope that my method of posting the schematic portion
of
what I a working with is not too obtuse. Couldn't figure out any other
way
to do it...

Many thanks...

Dave




You're wasting a gross amount of current in that bias network. How about
a nice MOSFET?


I've seen LDRs fry from too much light+current. I humbly suggest


Say a 2N7002, source to V-, drain to series resistor+LED, LDR plus pot to
set turn-on level:

(V+)----*----------------*
| |
R R
R R
R R
| R
*---* |
| | ---
| R \ / -----
*- R ----- -----
R |
R | | D
| | |---*
| | |--; 2N7000
*----------J |---*
| | | S
| |
L |
D |
R |
| |
| |
(V-)----*----------------*




John

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Default Using a photoresistor and light to turn a transistor OFF...

On 10/08/2011 06:06 PM, John Larkin wrote:
On Fri, 07 Oct 2011 07:26:02 -0400, Phil Hobbs
wrote:

On 10/07/2011 07:13 AM, Dave wrote:
"Phil wrote in message
...
On 10/07/2011 06:36 AM, Dave wrote:
As per my post in SEB, I am trying to use a photo resistor and sunlight
to
turn off a transistor that would otherwise be conducting like crazy, but
can't quite make the leap of comprehension as to how to actually do this.
Please see attached schematic parts that show more or less what I am
trying
to do this with. No part number for the photoresistor, sorry. It drops
from multi-megohms in the dark to single-digit Ohms in the light and
seems
perfectly capable of carrying the 30 to 50 mA current I am working with
at
the voltages indicated. Would really appreciate it if someone could
offer a
hint as to how I should proceed with as few components as possible (small
circuit board.) I hope that my method of posting the schematic portion
of
what I a working with is not too obtuse. Couldn't figure out any other
way
to do it...

Many thanks...

Dave




You're wasting a gross amount of current in that bias network. How about
a nice MOSFET?


I've seen LDRs fry from too much light+current. I humbly suggest


Say a 2N7002, source to V-, drain to series resistor+LED, LDR plus pot to
set turn-on level:

(V+)----*----------------*
| |
R R
R R
R R
| R
*---* |
| | ---
| R \ / -----
*- R ----- -----
R |
R | | D
| | |---*
| | |--; 2N7000
*----------J |---*
| | | S
| |
L |
D |
R |
| |
| |
(V-)----*----------------*




John


I haven't seen one fry itself on a 5V supply, but I suppose it's
possible. The extra resistor is good insurance, for sure.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net
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Default Using a photoresistor and light to turn a transistor OFF...

On Sat, 08 Oct 2011 15:06:56 -0700, John Larkin
wrote:

I've seen LDRs fry from too much light+current. I humbly suggest


I've done that... cobbled together a circuit with zero calculating
and it worked like a champ- until summer came then direct sunlight was
enough to lower the resistance and raise the ambient and poof no more
LDR.
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Default Using a photoresistor and light to turn a transistor OFF...


default wrote in message
...
On Sat, 08 Oct 2011 15:06:56 -0700, John Larkin
wrote:

I've seen LDRs fry from too much light+current. I humbly suggest


I've done that... cobbled together a circuit with zero calculating
and it worked like a champ- until summer came then direct sunlight was
enough to lower the resistance and raise the ambient and poof no more
LDR.


Your LDR turned into a poof?!


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Default Using a photoresistor and light to turn a transistor OFF... - Night light.asc

On Fri, 7 Oct 2011 05:36:05 -0500, "Dave" wrote:

As per my post in SEB, I am trying to use a photo resistor and sunlight to
turn off a transistor that would otherwise be conducting like crazy, but
can't quite make the leap of comprehension as to how to actually do this.
Please see attached schematic parts that show more or less what I am trying
to do this with. No part number for the photoresistor, sorry. It drops
from multi-megohms in the dark to single-digit Ohms in the light and seems
perfectly capable of carrying the 30 to 50 mA current I am working with at
the voltages indicated. Would really appreciate it if someone could offer a
hint as to how I should proceed with as few components as possible (small
circuit board.) I hope that my method of posting the schematic portion of
what I a working with is not too obtuse. Couldn't figure out any other way
to do it...


---
While Petrus' suggestion to use the PV array as the sensor is
excellent, it has the drawback that setting the switching point and
getting a nice "snap" into the LED is difficult, if not impossible,
using a single transistor.

Using a comparator capable of driving a 50 mA load solves both
problems at once.

I've attached an LTspice circuit list as a .asc file, and it should
run if you click on it and you've got LTspice installed on your
machine.

If not, here it is for all of you folks who might be interested but
can't get to abse:

Version 4
SHEET 1 1260 680
WIRE -256 -32 -304 -32
WIRE -128 -32 -192 -32
WIRE -32 -32 -128 -32
WIRE 208 -32 64 -32
WIRE 480 -32 432 -32
WIRE 704 -32 544 -32
WIRE 800 -32 704 -32
WIRE 944 -32 800 -32
WIRE 976 -32 944 -32
WIRE 1088 -32 1056 -32
WIRE 800 0 800 -32
WIRE 1088 16 1088 -32
WIRE 208 32 208 -32
WIRE 944 80 944 -32
WIRE -304 112 -304 -32
WIRE -96 112 -304 112
WIRE 16 112 16 32
WIRE 16 112 -16 112
WIRE 800 112 800 80
WIRE 912 112 800 112
WIRE 1088 128 1088 80
WIRE 1088 128 992 128
WIRE 432 144 432 -32
WIRE 480 144 432 144
WIRE 608 144 560 144
WIRE 880 144 608 144
WIRE 912 144 880 144
WIRE -304 176 -304 112
WIRE -128 176 -128 -32
WIRE 16 176 16 112
WIRE 208 176 208 112
WIRE 432 176 432 144
WIRE 704 176 704 -32
WIRE 928 192 928 176
WIRE 944 192 944 176
WIRE 944 192 928 192
WIRE 608 224 608 144
WIRE 800 224 800 112
WIRE 880 256 880 144
WIRE 976 256 880 256
WIRE 1088 256 1088 128
WIRE 1088 256 1056 256
WIRE -304 288 -304 256
WIRE -128 288 -128 256
WIRE 432 288 432 256
WIRE 704 288 704 256
WIRE -304 400 -304 368
WIRE -128 400 -128 368
WIRE -128 400 -304 400
WIRE 16 400 16 256
WIRE 16 400 -128 400
WIRE 208 400 208 240
WIRE 208 400 16 400
WIRE 432 400 432 368
WIRE 608 400 608 304
WIRE 608 400 432 400
WIRE 704 400 704 368
WIRE 704 400 608 400
WIRE 800 400 800 304
WIRE 800 400 704 400
WIRE 944 400 944 192
WIRE 944 400 800 400
WIRE -304 448 -304 400
WIRE 432 448 432 400
FLAG 432 448 0
FLAG -304 448 0
SYMBOL res 1072 -48 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 150
SYMBOL LED 1072 16 R0
SYMATTR InstName D1
SYMATTR Value NSSWS108T
SYMBOL voltage 432 272 R0
WINDOW 3 24 96 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value PULSE(0 16 0 12 0 0 24)
SYMBOL schottky 480 -16 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D2
SYMATTR Value 1N5817
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL voltage 704 272 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value 12
SYMBOL res 688 160 R0
SYMATTR InstName R2
SYMATTR Value .1
SYMBOL res 784 208 R0
SYMATTR InstName R3
SYMATTR Value 50k
SYMBOL Comparators\\LT1011 944 128 R0
WINDOW 0 53 20 Left 2
WINDOW 3 46 47 Left 2
SYMATTR InstName U1
SYMBOL res 816 96 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 100k
SYMBOL res 416 160 R0
SYMATTR InstName R5
SYMATTR Value 10
SYMBOL res 576 128 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R6
SYMATTR Value 100k
SYMBOL pnp 64 32 M270
SYMATTR InstName Q1
SYMATTR Value 2N3906
SYMBOL res 224 128 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R7
SYMATTR Value 150
SYMBOL LED 192 176 R0
SYMATTR InstName D3
SYMATTR Value NSSWS108T
SYMBOL voltage -304 272 R0
WINDOW 3 24 96 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V3
SYMATTR Value PULSE(0 16 0 12 0 0 24)
SYMBOL schottky -256 -16 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D4
SYMATTR Value 1N5817
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL voltage -128 272 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V4
SYMATTR Value 12
SYMBOL res -144 160 R0
SYMATTR InstName R8
SYMATTR Value .1
SYMBOL res -320 160 R0
SYMATTR InstName R9
SYMATTR Value 10
SYMBOL res 0 96 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R10
SYMATTR Value 1k
SYMBOL res 32 272 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R11
SYMATTR Value 100k
SYMBOL res 1072 240 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R12
SYMATTR Value 1meg
SYMBOL res 592 208 R0
WINDOW 0 -52 32 Left 2
WINDOW 3 -55 59 Left 2
SYMATTR InstName R13
SYMATTR Value 150k
TEXT -290 424 Left 2 !.tran 12


Notice that R10 R11 sets the switching "point" for Q1, but also smears
the ON to OFF period of D3 over a very wide range.

R4 R3 sets the switching point for U1, which then switches D1 ON and
OFF very quickly, no matter where the switching point lies.

BTW, I've crossposted this to sed and seb.


--
JF




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Posts: 93
Default Using a photoresistor and light to turn a transistor OFF... - Night light.asc


"John Fields" schreef in bericht
...
On Fri, 7 Oct 2011 05:36:05 -0500, "Dave" wrote:

As per my post in SEB, I am trying to use a photo resistor and sunlight to
turn off a transistor that would otherwise be conducting like crazy, but
can't quite make the leap of comprehension as to how to actually do this.
Please see attached schematic parts that show more or less what I am
trying
to do this with. No part number for the photoresistor, sorry. It drops
from multi-megohms in the dark to single-digit Ohms in the light and seems
perfectly capable of carrying the 30 to 50 mA current I am working with at
the voltages indicated. Would really appreciate it if someone could offer
a
hint as to how I should proceed with as few components as possible (small
circuit board.) I hope that my method of posting the schematic portion of
what I a working with is not too obtuse. Couldn't figure out any other
way
to do it...


---
While Petrus' suggestion to use the PV array as the sensor is
excellent, it has the drawback that setting the switching point and
getting a nice "snap" into the LED is difficult, if not impossible,
using a single transistor.

Using a comparator capable of driving a 50 mA load solves both
problems at once.

I've attached an LTspice circuit list as a .asc file, and it should
run if you click on it and you've got LTspice installed on your
machine.

If not, here it is for all of you folks who might be interested but
can't get to abse:

Version 4
SHEET 1 1260 680
WIRE -256 -32 -304 -32
WIRE -128 -32 -192 -32
WIRE -32 -32 -128 -32
WIRE 208 -32 64 -32
WIRE 480 -32 432 -32
WIRE 704 -32 544 -32
WIRE 800 -32 704 -32
WIRE 944 -32 800 -32
WIRE 976 -32 944 -32
WIRE 1088 -32 1056 -32
WIRE 800 0 800 -32
WIRE 1088 16 1088 -32
WIRE 208 32 208 -32
WIRE 944 80 944 -32
WIRE -304 112 -304 -32
WIRE -96 112 -304 112
WIRE 16 112 16 32
WIRE 16 112 -16 112
WIRE 800 112 800 80
WIRE 912 112 800 112
WIRE 1088 128 1088 80
WIRE 1088 128 992 128
WIRE 432 144 432 -32
WIRE 480 144 432 144
WIRE 608 144 560 144
WIRE 880 144 608 144
WIRE 912 144 880 144
WIRE -304 176 -304 112
WIRE -128 176 -128 -32
WIRE 16 176 16 112
WIRE 208 176 208 112
WIRE 432 176 432 144
WIRE 704 176 704 -32
WIRE 928 192 928 176
WIRE 944 192 944 176
WIRE 944 192 928 192
WIRE 608 224 608 144
WIRE 800 224 800 112
WIRE 880 256 880 144
WIRE 976 256 880 256
WIRE 1088 256 1088 128
WIRE 1088 256 1056 256
WIRE -304 288 -304 256
WIRE -128 288 -128 256
WIRE 432 288 432 256
WIRE 704 288 704 256
WIRE -304 400 -304 368
WIRE -128 400 -128 368
WIRE -128 400 -304 400
WIRE 16 400 16 256
WIRE 16 400 -128 400
WIRE 208 400 208 240
WIRE 208 400 16 400
WIRE 432 400 432 368
WIRE 608 400 608 304
WIRE 608 400 432 400
WIRE 704 400 704 368
WIRE 704 400 608 400
WIRE 800 400 800 304
WIRE 800 400 704 400
WIRE 944 400 944 192
WIRE 944 400 800 400
WIRE -304 448 -304 400
WIRE 432 448 432 400
FLAG 432 448 0
FLAG -304 448 0
SYMBOL res 1072 -48 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 150
SYMBOL LED 1072 16 R0
SYMATTR InstName D1
SYMATTR Value NSSWS108T
SYMBOL voltage 432 272 R0
WINDOW 3 24 96 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value PULSE(0 16 0 12 0 0 24)
SYMBOL schottky 480 -16 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D2
SYMATTR Value 1N5817
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL voltage 704 272 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value 12
SYMBOL res 688 160 R0
SYMATTR InstName R2
SYMATTR Value .1
SYMBOL res 784 208 R0
SYMATTR InstName R3
SYMATTR Value 50k
SYMBOL Comparators\\LT1011 944 128 R0
WINDOW 0 53 20 Left 2
WINDOW 3 46 47 Left 2
SYMATTR InstName U1
SYMBOL res 816 96 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 100k
SYMBOL res 416 160 R0
SYMATTR InstName R5
SYMATTR Value 10
SYMBOL res 576 128 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R6
SYMATTR Value 100k
SYMBOL pnp 64 32 M270
SYMATTR InstName Q1
SYMATTR Value 2N3906
SYMBOL res 224 128 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R7
SYMATTR Value 150
SYMBOL LED 192 176 R0
SYMATTR InstName D3
SYMATTR Value NSSWS108T
SYMBOL voltage -304 272 R0
WINDOW 3 24 96 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V3
SYMATTR Value PULSE(0 16 0 12 0 0 24)
SYMBOL schottky -256 -16 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D4
SYMATTR Value 1N5817
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL voltage -128 272 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V4
SYMATTR Value 12
SYMBOL res -144 160 R0
SYMATTR InstName R8
SYMATTR Value .1
SYMBOL res -320 160 R0
SYMATTR InstName R9
SYMATTR Value 10
SYMBOL res 0 96 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R10
SYMATTR Value 1k
SYMBOL res 32 272 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R11
SYMATTR Value 100k
SYMBOL res 1072 240 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R12
SYMATTR Value 1meg
SYMBOL res 592 208 R0
WINDOW 0 -52 32 Left 2
WINDOW 3 -55 59 Left 2
SYMATTR InstName R13
SYMATTR Value 150k
TEXT -290 424 Left 2 !.tran 12


Notice that R10 R11 sets the switching "point" for Q1, but also smears
the ON to OFF period of D3 over a very wide range.

R4 R3 sets the switching point for U1, which then switches D1 ON and
OFF very quickly, no matter where the switching point lies.

BTW, I've crossposted this to sed and seb.


--
JF



I considered the use of a comparator though not the LT1011 but the LM393 or
similar. FAIK more popular, almost everywhere available and maybe cheaper as
well.

The next thing could be a two transistor Schmitt trigger. I ever calculated
every component of it and I can still do so. It's just a matter of setting
the threshold and the hysteresis to the required values.

But the one transistor solution struck me for it's simplicity, low component
count and light effect. So when the (sun)light is fading, the LED starts to
glow faintly to come to full brightness when it grows really dark. Next
morning the other way around if there's enough energy left in the battery
that is.

petrus bitbyter


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Posts: 2,022
Default Using a photoresistor and light to turn a transistor OFF... - Night light.asc

On Sun, 9 Oct 2011 23:15:44 +0200, "petrus bitbyter"
wrote:


"John Fields" schreef in bericht
.. .
On Fri, 7 Oct 2011 05:36:05 -0500, "Dave" wrote:

As per my post in SEB, I am trying to use a photo resistor and sunlight to
turn off a transistor that would otherwise be conducting like crazy, but
can't quite make the leap of comprehension as to how to actually do this.
Please see attached schematic parts that show more or less what I am
trying
to do this with. No part number for the photoresistor, sorry. It drops
from multi-megohms in the dark to single-digit Ohms in the light and seems
perfectly capable of carrying the 30 to 50 mA current I am working with at
the voltages indicated. Would really appreciate it if someone could offer
a
hint as to how I should proceed with as few components as possible (small
circuit board.) I hope that my method of posting the schematic portion of
what I a working with is not too obtuse. Couldn't figure out any other
way
to do it...


---
While Petrus' suggestion to use the PV array as the sensor is
excellent, it has the drawback that setting the switching point and
getting a nice "snap" into the LED is difficult, if not impossible,
using a single transistor.

Using a comparator capable of driving a 50 mA load solves both
problems at once.


..
..
..

I considered the use of a comparator though not the LT1011 but the LM393 or
similar. FAIK more popular, almost everywhere available and maybe cheaper as
well.


---
Indeed, but incapable of handling, by itself, the 50mA load current
the OP was asking for.

The LT1011 is an improved LM311 clone and I used it because it was in
Linear's library, but an LM311 would work just as well for about 1/4
the price, qty 1.
---

The next thing could be a two transistor Schmitt trigger. I ever calculated
every component of it and I can still do so. It's just a matter of setting
the threshold and the hysteresis to the required values.


---
Post a schematic, please?
---

But the one transistor solution struck me for it's simplicity, low component
count and light effect. So when the (sun)light is fading, the LED starts to
glow faintly to come to full brightness when it grows really dark. Next
morning the other way around if there's enough energy left in the battery
that is.


---
Yup!

--
JF
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Posts: 1,001
Default Using a photoresistor and light to turn a transistor OFF... -Night light.asc

petrus bitbyter wrote:

"John Fields" schreef in bericht
...

On Fri, 7 Oct 2011 05:36:05 -0500, "Dave" wrote:


As per my post in SEB, I am trying to use a photo resistor and sunlight to
turn off a transistor that would otherwise be conducting like crazy, but
can't quite make the leap of comprehension as to how to actually do this.
Please see attached schematic parts that show more or less what I am
trying
to do this with. No part number for the photoresistor, sorry. It drops


from multi-megohms in the dark to single-digit Ohms in the light and seems


perfectly capable of carrying the 30 to 50 mA current I am working with at
the voltages indicated. Would really appreciate it if someone could offer
a
hint as to how I should proceed with as few components as possible (small
circuit board.) I hope that my method of posting the schematic portion of
what I a working with is not too obtuse. Couldn't figure out any other
way
to do it...


---
While Petrus' suggestion to use the PV array as the sensor is
excellent, it has the drawback that setting the switching point and
getting a nice "snap" into the LED is difficult, if not impossible,
using a single transistor.

Using a comparator capable of driving a 50 mA load solves both
problems at once.

I've attached an LTspice circuit list as a .asc file, and it should
run if you click on it and you've got LTspice installed on your
machine.

If not, here it is for all of you folks who might be interested but
can't get to abse:

Version 4
SHEET 1 1260 680
WIRE -256 -32 -304 -32
WIRE -128 -32 -192 -32
WIRE -32 -32 -128 -32
WIRE 208 -32 64 -32
WIRE 480 -32 432 -32
WIRE 704 -32 544 -32
WIRE 800 -32 704 -32
WIRE 944 -32 800 -32
WIRE 976 -32 944 -32
WIRE 1088 -32 1056 -32
WIRE 800 0 800 -32
WIRE 1088 16 1088 -32
WIRE 208 32 208 -32
WIRE 944 80 944 -32
WIRE -304 112 -304 -32
WIRE -96 112 -304 112
WIRE 16 112 16 32
WIRE 16 112 -16 112
WIRE 800 112 800 80
WIRE 912 112 800 112
WIRE 1088 128 1088 80
WIRE 1088 128 992 128
WIRE 432 144 432 -32
WIRE 480 144 432 144
WIRE 608 144 560 144
WIRE 880 144 608 144
WIRE 912 144 880 144
WIRE -304 176 -304 112
WIRE -128 176 -128 -32
WIRE 16 176 16 112
WIRE 208 176 208 112
WIRE 432 176 432 144
WIRE 704 176 704 -32
WIRE 928 192 928 176
WIRE 944 192 944 176
WIRE 944 192 928 192
WIRE 608 224 608 144
WIRE 800 224 800 112
WIRE 880 256 880 144
WIRE 976 256 880 256
WIRE 1088 256 1088 128
WIRE 1088 256 1056 256
WIRE -304 288 -304 256
WIRE -128 288 -128 256
WIRE 432 288 432 256
WIRE 704 288 704 256
WIRE -304 400 -304 368
WIRE -128 400 -128 368
WIRE -128 400 -304 400
WIRE 16 400 16 256
WIRE 16 400 -128 400
WIRE 208 400 208 240
WIRE 208 400 16 400
WIRE 432 400 432 368
WIRE 608 400 608 304
WIRE 608 400 432 400
WIRE 704 400 704 368
WIRE 704 400 608 400
WIRE 800 400 800 304
WIRE 800 400 704 400
WIRE 944 400 944 192
WIRE 944 400 800 400
WIRE -304 448 -304 400
WIRE 432 448 432 400
FLAG 432 448 0
FLAG -304 448 0
SYMBOL res 1072 -48 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R1
SYMATTR Value 150
SYMBOL LED 1072 16 R0
SYMATTR InstName D1
SYMATTR Value NSSWS108T
SYMBOL voltage 432 272 R0
WINDOW 3 24 96 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V1
SYMATTR Value PULSE(0 16 0 12 0 0 24)
SYMBOL schottky 480 -16 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D2
SYMATTR Value 1N5817
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL voltage 704 272 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V2
SYMATTR Value 12
SYMBOL res 688 160 R0
SYMATTR InstName R2
SYMATTR Value .1
SYMBOL res 784 208 R0
SYMATTR InstName R3
SYMATTR Value 50k
SYMBOL Comparators\\LT1011 944 128 R0
WINDOW 0 53 20 Left 2
WINDOW 3 46 47 Left 2
SYMATTR InstName U1
SYMBOL res 816 96 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R4
SYMATTR Value 100k
SYMBOL res 416 160 R0
SYMATTR InstName R5
SYMATTR Value 10
SYMBOL res 576 128 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R6
SYMATTR Value 100k
SYMBOL pnp 64 32 M270
SYMATTR InstName Q1
SYMATTR Value 2N3906
SYMBOL res 224 128 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R7
SYMATTR Value 150
SYMBOL LED 192 176 R0
SYMATTR InstName D3
SYMATTR Value NSSWS108T
SYMBOL voltage -304 272 R0
WINDOW 3 24 96 Invisible 2
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V3
SYMATTR Value PULSE(0 16 0 12 0 0 24)
SYMBOL schottky -256 -16 R270
WINDOW 0 32 32 VTop 2
WINDOW 3 0 32 VBottom 2
SYMATTR InstName D4
SYMATTR Value 1N5817
SYMATTR Description Diode
SYMATTR Type diode
SYMBOL voltage -128 272 R0
WINDOW 123 0 0 Left 2
WINDOW 39 0 0 Left 2
SYMATTR InstName V4
SYMATTR Value 12
SYMBOL res -144 160 R0
SYMATTR InstName R8
SYMATTR Value .1
SYMBOL res -320 160 R0
SYMATTR InstName R9
SYMATTR Value 10
SYMBOL res 0 96 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R10
SYMATTR Value 1k
SYMBOL res 32 272 R180
WINDOW 0 36 76 Left 2
WINDOW 3 36 40 Left 2
SYMATTR InstName R11
SYMATTR Value 100k
SYMBOL res 1072 240 R90
WINDOW 0 0 56 VBottom 2
WINDOW 3 32 56 VTop 2
SYMATTR InstName R12
SYMATTR Value 1meg
SYMBOL res 592 208 R0
WINDOW 0 -52 32 Left 2
WINDOW 3 -55 59 Left 2
SYMATTR InstName R13
SYMATTR Value 150k
TEXT -290 424 Left 2 !.tran 12


Notice that R10 R11 sets the switching "point" for Q1, but also smears
the ON to OFF period of D3 over a very wide range.

R4 R3 sets the switching point for U1, which then switches D1 ON and
OFF very quickly, no matter where the switching point lies.

BTW, I've crossposted this to sed and seb.


--
JF




I considered the use of a comparator though not the LT1011 but the LM393 or
similar. FAIK more popular, almost everywhere available and maybe cheaper as
well.

The next thing could be a two transistor Schmitt trigger. I ever calculated
every component of it and I can still do so. It's just a matter of setting
the threshold and the hysteresis to the required values.

But the one transistor solution struck me for it's simplicity, low component
count and light effect. So when the (sun)light is fading, the LED starts to
glow faintly to come to full brightness when it grows really dark. Next
morning the other way around if there's enough energy left in the battery
that is.

petrus bitbyter






47
___
+---------+-----+-|___|+-----------+
| | |
+ + |
3V bat--- | |
- - |
| ^ Vf 50 LED V -
| + Sch -
=== | |
GND | +
| |
+------------------+ +
| | | 10K
| | | ___
+ | PNP |--|___|-+
| | /| |
- | + |
--- 3 Volt PV | | |
| | | |
| + |
GND | GND |
| |
| |
+-----------------+



Something like that?

P.S.
That circuit should also charge. Use 50mv Vf Schottky diode.

The only problem is, you need at least 3 volts from the PV






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Posts: 2,022
Default Using a photoresistor and light to turn a transistor OFF... - Night light.asc

On Sun, 09 Oct 2011 19:32:36 -0400, Jamie
t wrote:


47
___
+---------+-----+-|___|+-----------+
| | |
+ + |
3V bat--- | |
- - |
| ^ Vf 50 LED V -
| + Sch -
=== | |
GND | +
| |
+------------------+ +
| | | 10K
| | | ___
+ | PNP |--|___|-+
| | /| |
- | + |
--- 3 Volt PV | | |
| | | |
| + |
GND | GND |
| |
| |
+-----------------+



Something like that?

P.S.
That circuit should also charge. Use 50mv Vf Schottky diode.


---
50mV???

Got a part number?
---

The only problem is, you need at least 3 volts from the PV


---
3V from the PV won't cut it, since the Schottky's in the way and
you'll need more than 3v to charge the battery.

--
JF
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Posts: 1,001
Default Using a photoresistor and light to turn a transistor OFF... -Night light.asc

John Fields wrote:

On Sun, 09 Oct 2011 19:32:36 -0400, Jamie
t wrote:



47
___
+---------+-----+-|___|+-----------+
| | |
+ + |
3V bat--- | |
- - |
| ^ Vf 50 LED V -
| + Sch -
=== | |
GND | +
| |
+------------------+ +
| | | 10K
| | | ___
+ | PNP |--|___|-+
| | /| |
- | + |
--- 3 Volt PV | | |
| | | |
| + |
GND | GND |
| |
| |
+-----------------+



Something like that?

P.S.
That circuit should also charge. Use 50mv Vf Schottky diode.



---
50mV???

Got a part number?
---


The only problem is, you need at least 3 volts from the PV



---
3V from the PV won't cut it, since the Schottky's in the way and
you'll need more than 3v to charge the battery.

it's 50mv with low load...that of course goes up as the current does.
for low I, a 1N5817 will reach that point. It depends on how you use it.

I actually meant to say the Rs = 0.050; Much better than the usual
0.5xxxx found in others.

As for the PV voltage, how else was this suppose to work? I didn't see
a voltage multiplier in the request, and they do make multi cell PV's, I
have a whole drive way full of LED lights with multi-cell PVs in them.

Jamie





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Default Using a photoresistor and light to turn a transistor OFF... - Night light.asc


"John Fields" schreef in bericht
...
On Sun, 9 Oct 2011 23:15:44 +0200, "petrus bitbyter"
wrote:


"John Fields" schreef in bericht
. ..
On Fri, 7 Oct 2011 05:36:05 -0500, "Dave" wrote:

As per my post in SEB, I am trying to use a photo resistor and sunlight
to
turn off a transistor that would otherwise be conducting like crazy, but
can't quite make the leap of comprehension as to how to actually do
this.
Please see attached schematic parts that show more or less what I am
trying
to do this with. No part number for the photoresistor, sorry. It drops
from multi-megohms in the dark to single-digit Ohms in the light and
seems
perfectly capable of carrying the 30 to 50 mA current I am working with
at
the voltages indicated. Would really appreciate it if someone could
offer
a
hint as to how I should proceed with as few components as possible
(small
circuit board.) I hope that my method of posting the schematic portion
of
what I a working with is not too obtuse. Couldn't figure out any other
way
to do it...

---
While Petrus' suggestion to use the PV array as the sensor is
excellent, it has the drawback that setting the switching point and
getting a nice "snap" into the LED is difficult, if not impossible,
using a single transistor.

Using a comparator capable of driving a 50 mA load solves both
problems at once.


.
.
.

I considered the use of a comparator though not the LT1011 but the LM393
or
similar. FAIK more popular, almost everywhere available and maybe cheaper
as
well.


---
Indeed, but incapable of handling, by itself, the 50mA load current
the OP was asking for.

The LT1011 is an improved LM311 clone and I used it because it was in
Linear's library, but an LM311 would work just as well for about 1/4
the price, qty 1.
---

The next thing could be a two transistor Schmitt trigger. I ever
calculated
every component of it and I can still do so. It's just a matter of setting
the threshold and the hysteresis to the required values.


---
Post a schematic, please?
---

But the one transistor solution struck me for it's simplicity, low
component
count and light effect. So when the (sun)light is fading, the LED starts
to
glow faintly to come to full brightness when it grows really dark. Next
morning the other way around if there's enough energy left in the battery
that is.


---
Yup!

--
JF


The LED mentioned by the OP can handle a maximum current of 30mA. The series
resistor of 160R reduces this to about 10mA, depending on the forward
voltage of the LED. So a LM311 would be a good option using a comparator.

A two transistor Schmitt-trigger is a classic. See below. I'm sure it'll
work though I made no extensive calculations this time.

+ solar-----+----|------+----------------------+-------+
cell | 1N5817 | | |
| | V LED |
| | - |
| | | |
| | | |
.-. .-. .-. |
| | | | | | |
| |22k | |1k5 | |47 | +4V8
'-' '-' '-' ---
| | ___ | -
| +-----|___|----+ | |
| | 3k3 | | |
| | | |/ ---
| ___ |/ +-----| BC547 -
+--|___|---| BC547 | | |
| 680 | | | |
| | | | ---
| +-----+--------)-------+ -
| | | |
| | | |
.-. .-. .-. ---
| | | | | | -
| |3k9 | |100 | |3k9 |
'-' '-' '-' |
| | | |
| | | |
- solar---+------------------+--------+---------------+-- GND
cell
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

petrus bitbyter


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Default Using a photoresistor and light to turn a transistor OFF... - Night light.asc

On Sun, 09 Oct 2011 20:13:31 -0400, Jamie
t wrote:

John Fields wrote:

On Sun, 09 Oct 2011 19:32:36 -0400, Jamie
t wrote:



47
___
+---------+-----+-|___|+-----------+
| | |
+ + |
3V bat--- | |
- - |
| ^ Vf 50 LED V -
| + Sch -
=== | |
GND | +
| |
+------------------+ +
| | | 10K
| | | ___
+ | PNP |--|___|-+
| | /| |
- | + |
--- 3 Volt PV | | |
| | | |
| + |
GND | GND |
| |
| |
+-----------------+



Something like that?

P.S.
That circuit should also charge. Use 50mv Vf Schottky diode.



---
50mV???

Got a part number?
---


The only problem is, you need at least 3 volts from the PV



---
3V from the PV won't cut it, since the Schottky's in the way and
you'll need more than 3v to charge the battery.

it's 50mv with low load...that of course goes up as the current does.
for low I, a 1N5817 will reach that point. It depends on how you use it.


---
I just measured the current through a 1N5817 with a 50mV drop across
it, and it turned out to be 23 microamps, so if you're planning to
charge the battery with that I'm afraid it's going to take more than
just a day, even at full sun in the middle of the summer.
---

I actually meant to say the Rs = 0.050; Much better than the usual
0.5xxxx found in others.


---
Rs???

What are you talking about?
---

As for the PV voltage, how else was this suppose to work? I didn't see
a voltage multiplier in the request, and they do make multi cell PV's, I
have a whole drive way full of LED lights with multi-cell PVs in them.


---
Your schematic clearly states "3 Volt PV", so if you meant more
voltage than that you should have shown it.

Personally, I think you're trying to bull**** your way out of the
corner you've stupidly painted yourself into.

--
JF
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Default Using a photoresistor and light to turn a transistor OFF... - Night light.asc

On Mon, 10 Oct 2011 11:04:04 -0500, John Fields
wrote:

On Sun, 09 Oct 2011 20:13:31 -0400, Jamie
wrote:

John Fields wrote:

On Sun, 09 Oct 2011 19:32:36 -0400, Jamie
t wrote:



47
___
+---------+-----+-|___|+-----------+
| | |
+ + |
3V bat--- | |
- - |
| ^ Vf 50 LED V -
| + Sch -
=== | |
GND | +
| |
+------------------+ +
| | | 10K
| | | ___
+ | PNP |--|___|-+
| | /| |
- | + |
--- 3 Volt PV | | |
| | | |
| + |
GND | GND |
| |
| |
+-----------------+



Something like that?

P.S.
That circuit should also charge. Use 50mv Vf Schottky diode.


---
50mV???

Got a part number?
---


The only problem is, you need at least 3 volts from the PV


---
3V from the PV won't cut it, since the Schottky's in the way and
you'll need more than 3v to charge the battery.

it's 50mv with low load...that of course goes up as the current does.
for low I, a 1N5817 will reach that point. It depends on how you use it.


---
I just measured the current through a 1N5817 with a 50mV drop across
it, and it turned out to be 23 microamps, so if you're planning to
charge the battery with that I'm afraid it's going to take more than
just a day, even at full sun in the middle of the summer.
---

I actually meant to say the Rs = 0.050; Much better than the usual
0.5xxxx found in others.


---
Rs???

What are you talking about?


Diode series resistance, the ohmic part of a diode's behavior. It
usually only matters at higher currents. It has a positive TC, the
opposite of the junction's TC.


John

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Default My God, it WORKS!


"Phil Hobbs" wrote in message
...
On 10/07/2011 06:36 AM, Dave wrote:
As per my post in SEB, I am trying to use a photo resistor and sunlight
to
turn off a transistor that would otherwise be conducting like crazy, but
can't quite make the leap of comprehension as to how to actually do this.
Please see attached schematic parts that show more or less what I am
trying
to do this with. No part number for the photoresistor, sorry. It drops
from multi-megohms in the dark to single-digit Ohms in the light and
seems
perfectly capable of carrying the 30 to 50 mA current I am working with
at
the voltages indicated. Would really appreciate it if someone could
offer a
hint as to how I should proceed with as few components as possible (small
circuit board.) I hope that my method of posting the schematic portion
of
what I a working with is not too obtuse. Couldn't figure out any other
way
to do it...

Many thanks...

Dave




You're wasting a gross amount of current in that bias network. How about
a nice MOSFET?

Say a 2N7002, source to V-, drain to series resistor+LED, LDR plus pot to
set turn-on level:

(V+)----*----------------*
| |
| R
| R
| R
| R
*---* |
| | ---
| R \ / -----
*- R ----- -----
R |
R | | D
| | |---*
| | |--; 2N7000
*----------J |---*
| | | S
| |
L |
D |
R |
| |
| |
(V-)----*----------------*














--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net


Man that was easy. Just had to get the MOSFET. Thank you, Phil Hobbs.

I spent so much time wrestling with that other configuration, and this just
flew together. And damn, but it works nice. Much appreciated. The whole
thing goes into a mushroom lawn ornament, with the LED inside the mushroom
cap to shine down on the fairy sitting underneath at night. Gonna look nice
between the sage and Mexican Mint Merigold, which is a weed down in Mexico,
but grows great in Texas and tastes just like Tarragon (which absolutely
will not grow in Texas.)

Dave


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Default My God, it WORKS!

On Mon, 17 Oct 2011 17:53:01 -0500, "Dave" wrote:


"Phil Hobbs" wrote in message
...
On 10/07/2011 06:36 AM, Dave wrote:
As per my post in SEB, I am trying to use a photo resistor and sunlight
to
turn off a transistor that would otherwise be conducting like crazy, but
can't quite make the leap of comprehension as to how to actually do this.
Please see attached schematic parts that show more or less what I am
trying
to do this with. No part number for the photoresistor, sorry. It drops
from multi-megohms in the dark to single-digit Ohms in the light and
seems
perfectly capable of carrying the 30 to 50 mA current I am working with
at
the voltages indicated. Would really appreciate it if someone could
offer a
hint as to how I should proceed with as few components as possible (small
circuit board.) I hope that my method of posting the schematic portion
of
what I a working with is not too obtuse. Couldn't figure out any other
way
to do it...

Many thanks...

Dave




You're wasting a gross amount of current in that bias network. How about
a nice MOSFET?

Say a 2N7002, source to V-, drain to series resistor+LED, LDR plus pot to
set turn-on level:

(V+)----*----------------*
| |
| R
| R
| R
| R
*---* |
| | ---
| R \ / -----
*- R ----- -----
R |
R | | D
| | |---*
| | |--; 2N7000
*----------J |---*
| | | S
| |
L |
D |
R |
| |
| |
(V-)----*----------------*














--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net


Man that was easy. Just had to get the MOSFET. Thank you, Phil Hobbs.

I spent so much time wrestling with that other configuration, and this just
flew together. And damn, but it works nice. Much appreciated. The whole
thing goes into a mushroom lawn ornament, with the LED inside the mushroom
cap to shine down on the fairy sitting underneath at night. Gonna look nice
between the sage and Mexican Mint Merigold, which is a weed down in Mexico,
but grows great in Texas and tastes just like Tarragon (which absolutely
will not grow in Texas.)

Dave


A likely story ;-)

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.


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Posts: 635
Default My God, it WORKS!

On 10/17/2011 06:53 PM, Dave wrote:
"Phil wrote in message
...
On 10/07/2011 06:36 AM, Dave wrote:
As per my post in SEB, I am trying to use a photo resistor and sunlight
to
turn off a transistor that would otherwise be conducting like crazy, but
can't quite make the leap of comprehension as to how to actually do this.
Please see attached schematic parts that show more or less what I am
trying
to do this with. No part number for the photoresistor, sorry. It drops
from multi-megohms in the dark to single-digit Ohms in the light and
seems
perfectly capable of carrying the 30 to 50 mA current I am working with
at
the voltages indicated. Would really appreciate it if someone could
offer a
hint as to how I should proceed with as few components as possible (small
circuit board.) I hope that my method of posting the schematic portion
of
what I a working with is not too obtuse. Couldn't figure out any other
way
to do it...

Many thanks...

Dave




You're wasting a gross amount of current in that bias network. How about
a nice MOSFET?

Say a 2N7002, source to V-, drain to series resistor+LED, LDR plus pot to
set turn-on level:

(V+)----*----------------*
| |
| R
| R
| R
| R
*---* |
| | ---
| R \ / -----
*- R ----- -----
R |
R | | D
| | |---*
| | |--; 2N7000
*----------J |---*
| | | S
| |
L |
D |
R |
| |
| |
(V-)----*----------------*




Man that was easy. Just had to get the MOSFET. Thank you, Phil Hobbs.

I spent so much time wrestling with that other configuration, and this just
flew together. And damn, but it works nice. Much appreciated. The whole
thing goes into a mushroom lawn ornament, with the LED inside the mushroom
cap to shine down on the fairy sitting underneath at night. Gonna look nice
between the sage and Mexican Mint Merigold, which is a weed down in Mexico,
but grows great in Texas and tastes just like Tarragon (which absolutely
will not grow in Texas.)

Dave


You're welcome. As the wise man said about beer, 2N7000s are "Good for
what ails ya, and if nothing ails ya, it's good for that too."

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net
  #27   Report Post  
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Default My God, it WORKS!


"Phil Hobbs" wrote in message
...
On 10/17/2011 06:53 PM, Dave wrote:
"Phil wrote in message
...
On 10/07/2011 06:36 AM, Dave wrote:
As per my post in SEB, I am trying to use a photo resistor and sunlight
to
turn off a transistor that would otherwise be conducting like crazy,
but
can't quite make the leap of comprehension as to how to actually do
this.
Please see attached schematic parts that show more or less what I am
trying
to do this with. No part number for the photoresistor, sorry. It
drops
from multi-megohms in the dark to single-digit Ohms in the light and
seems
perfectly capable of carrying the 30 to 50 mA current I am working with
at
the voltages indicated. Would really appreciate it if someone could
offer a
hint as to how I should proceed with as few components as possible
(small
circuit board.) I hope that my method of posting the schematic portion
of
what I a working with is not too obtuse. Couldn't figure out any other
way
to do it...

Many thanks...

Dave




You're wasting a gross amount of current in that bias network. How
about
a nice MOSFET?

Say a 2N7002, source to V-, drain to series resistor+LED, LDR plus pot
to
set turn-on level:

(V+)----*----------------*
| |
| R
| R
| R
| R
*---* |
| | ---
| R \ / -----
*- R ----- -----
R |
R | | D
| | |---*
| | |--; 2N7000
*----------J |---*
| | | S
| |
L |
D |
R |
| |
| |
(V-)----*----------------*




Man that was easy. Just had to get the MOSFET. Thank you, Phil Hobbs.

I spent so much time wrestling with that other configuration, and this
just
flew together. And damn, but it works nice. Much appreciated. The
whole
thing goes into a mushroom lawn ornament, with the LED inside the
mushroom
cap to shine down on the fairy sitting underneath at night. Gonna look
nice
between the sage and Mexican Mint Merigold, which is a weed down in
Mexico,
but grows great in Texas and tastes just like Tarragon (which absolutely
will not grow in Texas.)

Dave


You're welcome. As the wise man said about beer, 2N7000s are "Good for
what ails ya, and if nothing ails ya, it's good for that too."

Cheers

Phil Hobbs



LOL! And thank you for that belly laugh. shaking head Cheers to you,
sir!

D

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net



  #28   Report Post  
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Posts: 2,022
Default My God, it WORKS!

On Mon, 17 Oct 2011 20:41:06 -0500, "Dave" wrote:


"Phil Hobbs" wrote in message
...
On 10/17/2011 06:53 PM, Dave wrote:
"Phil wrote in message
...
On 10/07/2011 06:36 AM, Dave wrote:
As per my post in SEB, I am trying to use a photo resistor and sunlight
to
turn off a transistor that would otherwise be conducting like crazy,
but
can't quite make the leap of comprehension as to how to actually do
this.
Please see attached schematic parts that show more or less what I am
trying
to do this with. No part number for the photoresistor, sorry. It
drops
from multi-megohms in the dark to single-digit Ohms in the light and
seems
perfectly capable of carrying the 30 to 50 mA current I am working with
at
the voltages indicated. Would really appreciate it if someone could
offer a
hint as to how I should proceed with as few components as possible
(small
circuit board.) I hope that my method of posting the schematic portion
of
what I a working with is not too obtuse. Couldn't figure out any other
way
to do it...

Many thanks...

Dave




You're wasting a gross amount of current in that bias network. How
about
a nice MOSFET?

Say a 2N7002, source to V-, drain to series resistor+LED, LDR plus pot
to
set turn-on level:

(V+)----*----------------*
| |
| R
| R
| R
| R
*---* |
| | ---
| R \ / -----
*- R ----- -----
R |
R | | D
| | |---*
| | |--; 2N7000
*----------J |---*
| | | S
| |
L |
D |
R |
| |
| |
(V-)----*----------------*




Man that was easy. Just had to get the MOSFET. Thank you, Phil Hobbs.

I spent so much time wrestling with that other configuration, and this
just
flew together. And damn, but it works nice. Much appreciated.


---
Geez, I feel kind of miffed since my (Jan's) solution would allow you
to rid yourself of the LDR and its associated circuitry.

With that in mind, why would you find Doctor Phil's circuit, which is
wasteful of power and money by having it drive an unnecessary LDR,
superior to mine?

--
JF
  #29   Report Post  
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Posts: 328
Default My God, it WORKS!


"John Fields" wrote in message
...
On Mon, 17 Oct 2011 20:41:06 -0500, "Dave" wrote:


"Phil Hobbs" wrote in message
...
On 10/17/2011 06:53 PM, Dave wrote:
"Phil wrote in message
...
On 10/07/2011 06:36 AM, Dave wrote:
As per my post in SEB, I am trying to use a photo resistor and
sunlight
to
turn off a transistor that would otherwise be conducting like crazy,
but
can't quite make the leap of comprehension as to how to actually do
this.
Please see attached schematic parts that show more or less what I am
trying
to do this with. No part number for the photoresistor, sorry. It
drops
from multi-megohms in the dark to single-digit Ohms in the light and
seems
perfectly capable of carrying the 30 to 50 mA current I am working
with
at
the voltages indicated. Would really appreciate it if someone could
offer a
hint as to how I should proceed with as few components as possible
(small
circuit board.) I hope that my method of posting the schematic
portion
of
what I a working with is not too obtuse. Couldn't figure out any
other
way
to do it...

Many thanks...

Dave




You're wasting a gross amount of current in that bias network. How
about
a nice MOSFET?

Say a 2N7002, source to V-, drain to series resistor+LED, LDR plus pot
to
set turn-on level:

(V+)----*----------------*
| |
| R
| R
| R
| R
*---* |
| | ---
| R \ / -----
*- R ----- -----
R |
R | | D
| | |---*
| | |--; 2N7000
*----------J |---*
| | | S
| |
L |
D |
R |
| |
| |
(V-)----*----------------*




Man that was easy. Just had to get the MOSFET. Thank you, Phil Hobbs.

I spent so much time wrestling with that other configuration, and this
just
flew together. And damn, but it works nice. Much appreciated.


---
Geez, I feel kind of miffed since my (Jan's) solution would allow you
to rid yourself of the LDR and its associated circuitry.

With that in mind, why would you find Doctor Phil's circuit, which is
wasteful of power and money by having it drive an unnecessary LDR,
superior to mine?

--
JF


Hey John. No offense intended, believe me. Your ASCII description
translated into a schematic where my tiny photocell (I'm guessing that's
what V3 was) was set up as 4 VDC, rather than .4 VDC, which is what it
actually put out. And even then, when I set it all up, it looked like it
ought to work, but it didn't. No idea why, other than that there is
something about the tiny photocell that I don't know. Finally gave up on
using that component. When my Digikey parts came in I put them together and
they took off. That version worked, so I used it. Now I'm trying to find a
6V solar cell smaller than the 6"X6" behemoth I currenty have in place.
Will probably go with one from Amazon that is 4"X3" and flexible.

Take it easy...

Dave


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Default My God, it WORKS!

On Wed, 19 Oct 2011 13:05:27 -0500, "Dave" wrote:


"John Fields" wrote in message
.. .
On Mon, 17 Oct 2011 20:41:06 -0500, "Dave" wrote:


"Phil Hobbs" wrote in message
...
On 10/17/2011 06:53 PM, Dave wrote:
"Phil wrote in message
...
On 10/07/2011 06:36 AM, Dave wrote:
As per my post in SEB, I am trying to use a photo resistor and
sunlight
to
turn off a transistor that would otherwise be conducting like crazy,
but
can't quite make the leap of comprehension as to how to actually do
this.
Please see attached schematic parts that show more or less what I am
trying
to do this with. No part number for the photoresistor, sorry. It
drops
from multi-megohms in the dark to single-digit Ohms in the light and
seems
perfectly capable of carrying the 30 to 50 mA current I am working
with
at
the voltages indicated. Would really appreciate it if someone could
offer a
hint as to how I should proceed with as few components as possible
(small
circuit board.) I hope that my method of posting the schematic
portion
of
what I a working with is not too obtuse. Couldn't figure out any
other
way
to do it...

Many thanks...

Dave




You're wasting a gross amount of current in that bias network. How
about
a nice MOSFET?

Say a 2N7002, source to V-, drain to series resistor+LED, LDR plus pot
to
set turn-on level:

(V+)----*----------------*
| |
| R
| R
| R
| R
*---* |
| | ---
| R \ / -----
*- R ----- -----
R |
R | | D
| | |---*
| | |--; 2N7000
*----------J |---*
| | | S
| |
L |
D |
R |
| |
| |
(V-)----*----------------*




Man that was easy. Just had to get the MOSFET. Thank you, Phil Hobbs.

I spent so much time wrestling with that other configuration, and this
just
flew together. And damn, but it works nice. Much appreciated.


---
Geez, I feel kind of miffed since my (Jan's) solution would allow you
to rid yourself of the LDR and its associated circuitry.

With that in mind, why would you find Doctor Phil's circuit, which is
wasteful of power and money by having it drive an unnecessary LDR,
superior to mine?

--
JF


Hey John. No offense intended, believe me. Your ASCII description
translated into a schematic where my tiny photocell (I'm guessing that's
what V3 was) was set up as 4 VDC, rather than .4 VDC, which is what it
actually put out. And even then, when I set it all up, it looked like it
ought to work, but it didn't. No idea why, other than that there is
something about the tiny photocell that I don't know. Finally gave up on
using that component. When my Digikey parts came in I put them together and
they took off. That version worked, so I used it. Now I'm trying to find a
6V solar cell smaller than the 6"X6" behemoth I currenty have in place.
Will probably go with one from Amazon that is 4"X3" and flexible.


---
No problem, but the circuit I was referring to wasn't the one with the
tiny PV, it was the one with a PNP driving the LED which I posted as
an LTspice circuit list along with two other circuits.

Here it is in ASCII:

.. 2N3906
.. +-[1N5817]-+---------E C-+
.. | | B |
.. +-----------|-----+ | |
.. | | | | [42]
.. |+ |+ [POT]--+ |
.. [PV] [BAT] |10k [LED]
.. | | | |K
.. +-----------+-----+---------+

Notice no LDR and its associated resistor. :-)

Anyway, as long as you have something that works, that's what matters.

BTW, make sure that you get a PV array with the capacity to charge the
battery enough, during the day, so that the LED stays on for as long
as you need it to at night.

--
JF


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Posts: 328
Default My God, it WORKS!


"John Fields" wrote in message
...
On Wed, 19 Oct 2011 13:05:27 -0500, "Dave" wrote:


"John Fields" wrote in message
. ..
On Mon, 17 Oct 2011 20:41:06 -0500, "Dave" wrote:


"Phil Hobbs" wrote in message
...
On 10/17/2011 06:53 PM, Dave wrote:
"Phil wrote in
message
...
On 10/07/2011 06:36 AM, Dave wrote:
As per my post in SEB, I am trying to use a photo resistor and
sunlight
to
turn off a transistor that would otherwise be conducting like
crazy,
but
can't quite make the leap of comprehension as to how to actually do
this.
Please see attached schematic parts that show more or less what I
am
trying
to do this with. No part number for the photoresistor, sorry. It
drops
from multi-megohms in the dark to single-digit Ohms in the light
and
seems
perfectly capable of carrying the 30 to 50 mA current I am working
with
at
the voltages indicated. Would really appreciate it if someone
could
offer a
hint as to how I should proceed with as few components as possible
(small
circuit board.) I hope that my method of posting the schematic
portion
of
what I a working with is not too obtuse. Couldn't figure out any
other
way
to do it...

Many thanks...

Dave




You're wasting a gross amount of current in that bias network. How
about
a nice MOSFET?

Say a 2N7002, source to V-, drain to series resistor+LED, LDR plus
pot
to
set turn-on level:

(V+)----*----------------*
| |
| R
| R
| R
| R
*---* |
| | ---
| R \ / -----
*- R ----- -----
R |
R | | D
| | |---*
| | |--; 2N7000
*----------J |---*
| | | S
| |
L |
D |
R |
| |
| |
(V-)----*----------------*




Man that was easy. Just had to get the MOSFET. Thank you, Phil
Hobbs.

I spent so much time wrestling with that other configuration, and
this
just
flew together. And damn, but it works nice. Much appreciated.

---
Geez, I feel kind of miffed since my (Jan's) solution would allow you
to rid yourself of the LDR and its associated circuitry.

With that in mind, why would you find Doctor Phil's circuit, which is
wasteful of power and money by having it drive an unnecessary LDR,
superior to mine?

--
JF


Hey John. No offense intended, believe me. Your ASCII description
translated into a schematic where my tiny photocell (I'm guessing that's
what V3 was) was set up as 4 VDC, rather than .4 VDC, which is what it
actually put out. And even then, when I set it all up, it looked like it
ought to work, but it didn't. No idea why, other than that there is
something about the tiny photocell that I don't know. Finally gave up on
using that component. When my Digikey parts came in I put them together
and
they took off. That version worked, so I used it. Now I'm trying to find
a
6V solar cell smaller than the 6"X6" behemoth I currenty have in place.
Will probably go with one from Amazon that is 4"X3" and flexible.


---
No problem, but the circuit I was referring to wasn't the one with the
tiny PV, it was the one with a PNP driving the LED which I posted as
an LTspice circuit list along with two other circuits.

Here it is in ASCII:

. 2N3906
. +-[1N5817]-+---------E C-+
. | | B |
. +-----------|-----+ | |
. | | | | [42]
. |+ |+ [POT]--+ |
. [PV] [BAT] |10k [LED]
. | | | |K
. +-----------+-----+---------+

Notice no LDR and its associated resistor. :-)

Anyway, as long as you have something that works, that's what matters.

BTW, make sure that you get a PV array with the capacity to charge the
battery enough, during the day, so that the LED stays on for as long
as you need it to at night.

--
JF


Hey again. Oh, sorry, I missunderstood. Will have to go back and take
another look at that particular circuit. I didn't know if I had any
2N3906s, and didn't push it past that. Will definetly check it out though.

And yes, I am working to make sure that I am able to charge the batteries
sufficiently to keep things running as long as possible. Thanks for
mentioning that though, and the encouragement.

Take it easy...

D


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