On Tue, 24 Mar 2009 13:39:59 -0800, David Nebenzahl
wrote:

(famous last words, "simple circuit" ...)

OK, so I'm trying to come up with a simple (maybe even elegant) solution
to a simple problem. Have an idea I want to run by y'all.

Function: person has a motion-detector light installed in their home.
They want a buzzer/bell/annunciator of some kind to go off *momentarily*
whenever the light is activated.

Here's my idea for the circuit:
http://www.geocities.com/bonezphoto/...e-shotBell.gif

First of all, please don't laugh at this. I am *not* a double-E or in
any way an electronics expert. Also keep in mind that this is the
farthest thing from a mil-spec application. It's just for fun; no life
support medical devices will depend on it.

I'd like to know the following:

1. Will this circuit even work?
1a. Will it work but end up destroying one or more components?
2. Is there a simpler way of accomplishing this task?
3. If it'll work, what are the right component values?

Explanation:

D1 is a half-wave rectifier. C2 filters the DC to produce more-or-less
ripple-free current. C1 provides the momentary "on" signal, by charging,
then "shutting down" when charged (sized according to RC time constant
to provide the desired "on" time). R2 and R3 form a voltage divider to
supply the appropriate base voltage to Q1. R1 acts as a voltage divider
in series with the load to supply the appropriate output voltage. (I
chose 24 volts DC arbitrarily; it might be less, probably not more.)

Component sizing:

R1 would obviously have to be large enough (in terms of power capacity)
to handle the load. The load would probably have a minimal current draw.
And since it would only be "on" momentarily, R1 could probably be a bit
undersized without worrying about damage.

Q1 would also need to be large enough to handle the load. I'm thinking a
common TO-220 type might work fine.

R2 & R3 could be small 1/8 watters.

OK, have at it. Rip 'er apart!

I thibk you may want to check the orientation od D1.

Based on that, this might be safer:

Go to http://www.x10.com/products/pr511_ed_deal.html

Buy 2 motion sensor lights with an audio alert for $70.

Replace existing motion sensor light.

Plug in audio alert device.

Done.

(famous last words, "simple circuit" ...)

OK, so I'm trying to come up with a simple (maybe even elegant) solution
to a simple problem. Have an idea I want to run by y'all.

Function: person has a motion-detector light installed in their home.
They want a buzzer/bell/annunciator of some kind to go off *momentarily*
whenever the light is activated.

Here's my idea for the circuit:
http://www.geocities.com/bonezphoto/...e-shotBell.gif

First of all, please don't laugh at this. I am *not* a double-E or in
any way an electronics expert. Also keep in mind that this is the
farthest thing from a mil-spec application. It's just for fun; no life
support medical devices will depend on it.

I'd like to know the following:

1. Will this circuit even work?
1a. Will it work but end up destroying one or more components?
2. Is there a simpler way of accomplishing this task?
3. If it'll work, what are the right component values?

Explanation:

D1 is a half-wave rectifier. C2 filters the DC to produce more-or-less
ripple-free current. C1 provides the momentary "on" signal, by charging,
then "shutting down" when charged (sized according to RC time constant
to provide the desired "on" time). R2 and R3 form a voltage divider to
supply the appropriate base voltage to Q1. R1 acts as a voltage divider
in series with the load to supply the appropriate output voltage. (I
chose 24 volts DC arbitrarily; it might be less, probably not more.)

Component sizing:

R1 would obviously have to be large enough (in terms of power capacity)
to handle the load. The load would probably have a minimal current draw.
And since it would only be "on" momentarily, R1 could probably be a bit
undersized without worrying about damage.

Q1 would also need to be large enough to handle the load. I'm thinking a
common TO-220 type might work fine.

R2 & R3 could be small 1/8 watters.

OK, have at it. Rip 'er apart!


--
Made From Pears: Pretty good chance that the product is at least
mostly pears.
Made With Pears: Pretty good chance that pears will be detectable in
the product.
Contains Pears: One pear seed per multiple tons of product.

(with apologies to Dorothy L. Sayers)

On Mar 24, 2:39*pm, David Nebenzahl wrote:
(famous last words, "simple circuit" ...)


(famous last words, "what does this post have to do with electronics
repair"...)

(famous last words, "what does this post
have to do with electronics repair"...)

A lot... if the circuit damages something.

About 50 years ago, MAD ran a parody titled "Beatnik Magazine". One of its
contents was a photo of a middle-class family, watching TV in the living
room, with the caption "What's wrong with this picture?" The answer was
"Like, man, /everything/ is wrong with this picture."

That pretty applies to the circuit. I see what you're trying to do, but
you're going to get two exploded caps (at least), and possibly a small fire.

Take the other poster's advice. Buy a second detector and plug a 120V alarm
of some sort where the lamp goes. If the one you have an handle enough
current, you could always stick a plug adapter in the lamp socket.

"William Sommerwerck" wrote in
message ...
(famous last words, "what does this post
have to do with electronics repair"...)

A lot... if the circuit damages something.

About 50 years ago, MAD ran a parody titled "Beatnik
Magazine". One of its
contents was a photo of a middle-class family, watching TV
in the living
room, with the caption "What's wrong with this picture?"
The answer was
"Like, man, /everything/ is wrong with this picture."

That pretty applies to the circuit. I see what you're
trying to do, but
you're going to get two exploded caps (at least), and
possibly a small fire.

Take the other poster's advice. Buy a second detector and
plug a 120V alarm
of some sort where the lamp goes. If the one you have an
handle enough
current, you could always stick a plug adapter in the lamp
socket.

Actually the circuit is not all that unworkable. Some
suggestions and comments:

1) Diode D1 is backwards;
2) You need a resistor in series with D1 to limit in-rush
current;
3) There is no discharge path for C1. A high value resistor
across C2 can fix that;
4) What do expect to place across the terminals labeled 24
VDC? The voltage there may have no relation to 24 volts.

Further suggestions contingent upon knowing what is at the
24 VDC connection.

David

"David Nebenzahl" schreef in bericht
s.com...
(famous last words, "simple circuit" ...)

OK, so I'm trying to come up with a simple (maybe even elegant) solution
to a simple problem. Have an idea I want to run by y'all.

Function: person has a motion-detector light installed in their home.
They want a buzzer/bell/annunciator of some kind to go off *momentarily*
whenever the light is activated.

Here's my idea for the circuit:
http://www.geocities.com/bonezphoto/...e-shotBell.gif

First of all, please don't laugh at this. I am *not* a double-E or in any
way an electronics expert. Also keep in mind that this is the farthest
thing from a mil-spec application. It's just for fun; no life support
medical devices will depend on it.

I'd like to know the following:

1. Will this circuit even work?
1a. Will it work but end up destroying one or more components?
2. Is there a simpler way of accomplishing this task?
3. If it'll work, what are the right component values?

Explanation:

D1 is a half-wave rectifier. C2 filters the DC to produce more-or-less
ripple-free current. C1 provides the momentary "on" signal, by charging,
then "shutting down" when charged (sized according to RC time constant to
provide the desired "on" time). R2 and R3 form a voltage divider to supply
the appropriate base voltage to Q1. R1 acts as a voltage divider in series
with the load to supply the appropriate output voltage. (I chose 24 volts
DC arbitrarily; it might be less, probably not more.)

Component sizing:

R1 would obviously have to be large enough (in terms of power capacity) to
handle the load. The load would probably have a minimal current draw. And
since it would only be "on" momentarily, R1 could probably be a bit
undersized without worrying about damage.

Q1 would also need to be large enough to handle the load. I'm thinking a
common TO-220 type might work fine.

R2 & R3 could be small 1/8 watters.

OK, have at it. Rip 'er apart!


--
Made From Pears: Pretty good chance that the product is at least
mostly pears.
Made With Pears: Pretty good chance that pears will be detectable in
the product.
Contains Pears: One pear seed per multiple tons of product.

(with apologies to Dorothy L. Sayers)

It will not work at all and it'll take half a course in electronics to
explain why. I'm too tired to write that course.

petrus bitbyter

On Tue, 24 Mar 2009 13:39:59 -0800, David Nebenzahl
wrote:

(famous last words, "simple circuit" ...)

OK, so I'm trying to come up with a simple (maybe even elegant) solution
to a simple problem. Have an idea I want to run by y'all.

Function: person has a motion-detector light installed in their home.
They want a buzzer/bell/annunciator of some kind to go off *momentarily*
whenever the light is activated.

Here's my idea for the circuit:
http://www.geocities.com/bonezphoto/...e-shotBell.gif

First of all, please don't laugh at this. I am *not* a double-E or in
any way an electronics expert. Also keep in mind that this is the
farthest thing from a mil-spec application. It's just for fun; no life
support medical devices will depend on it.

I'd like to know the following:

1. Will this circuit even work?
1a. Will it work but end up destroying one or more components?
2. Is there a simpler way of accomplishing this task?
3. If it'll work, what are the right component values?

Explanation:

D1 is a half-wave rectifier. C2 filters the DC to produce more-or-less
ripple-free current. C1 provides the momentary "on" signal, by charging,
then "shutting down" when charged (sized according to RC time constant
to provide the desired "on" time). R2 and R3 form a voltage divider to
supply the appropriate base voltage to Q1. R1 acts as a voltage divider
in series with the load to supply the appropriate output voltage. (I
chose 24 volts DC arbitrarily; it might be less, probably not more.)

Component sizing:

R1 would obviously have to be large enough (in terms of power capacity)
to handle the load. The load would probably have a minimal current draw.
And since it would only be "on" momentarily, R1 could probably be a bit
undersized without worrying about damage.

Q1 would also need to be large enough to handle the load. I'm thinking a
common TO-220 type might work fine.

R2 & R3 could be small 1/8 watters.

OK, have at it. Rip 'er apart!

Reversing D1 and providing a bleeder resistor across C2 have already
been mentioned. I have two further suggestions.

1. Either provide a diode to prevent the base of Q1 going too far
negative with respect to it's emitter or size the bleeder resistor
(R4) so the time constant of C2-R4 is much greater than the time
constant of C1-R2+R3
2. Choose R1 to provide about a 140V drop across R1 at the buzzer's
rated current. Place a zener diode across the 24VDC terminals to
prevent excessive current flow through the buzzer.

Contrary to what several nay-sayers have expressed, this exercise has
a LOT to do with electronics repair. Any fool can keep replacing
components until he finds the bad one. The successful tech will be
able to analyse a circuit and make meaningful tests to identfy the
failing part.

NOW your next exercise is to identify the values for these components.


PlainBill

On 3/25/2009 5:24 AM David spake thus:

Actually the circuit is not all that unworkable. Some
suggestions and comments:

1) Diode D1 is backwards;
2) You need a resistor in series with D1 to limit in-rush
current;
3) There is no discharge path for C1. A high value resistor
across C2 can fix that;
4) What do expect to place across the terminals labeled 24
VDC? The voltage there may have no relation to 24 volts.

Further suggestions contingent upon knowing what is at the
24 VDC connection.

Thank you for not automatically dismissing the whole thing out of hand,
as other respondents obviously did. Not helpful.

OK, answers:

1. Yeah, it's a *drawing* error. I can still not remember which way is
which, graphically speaking, for the life of me. When I actually build
stuff I check and double-check diode anode-cathode connections, and
haven't gotten it wrong once. I guess I just need a good mnemonic to
remember which way the damn arrow points.

2. OK; I presume this needs to be the same size (power capacity) as the
resistor in series with the load, right?

3. OK.

4, 5: The load would be a small annunciator device: a doorbell, chime or
other sound-generating device, *probably* operating at 18-24 volts. I'm
guessing current draw would be in the low hundreds of mA, certainly less
than half an amp. Does that help?


--
Made From Pears: Pretty good chance that the product is at least
mostly pears.
Made With Pears: Pretty good chance that pears will be detectable in
the product.
Contains Pears: One pear seed per multiple tons of product.

(with apologies to Dorothy L. Sayers)

On 3/25/2009 5:24 AM David spake thus:

Actually the circuit is not all that unworkable. Some
suggestions and comments:

Check the updated schematic, incorporating your suggestions:
http://www.geocities.com/bonezphoto/...e-shotBell.gif

Let me know what you think.


--
Made From Pears: Pretty good chance that the product is at least
mostly pears.
Made With Pears: Pretty good chance that pears will be detectable in
the product.
Contains Pears: One pear seed per multiple tons of product.

(with apologies to Dorothy L. Sayers)

On 3/25/2009 5:24 AM David spake thus:

Actually the circuit is not all that unworkable. Some
suggestions and comments:

1) Diode D1 is backwards;
2) You need a resistor in series with D1 to limit in-rush
current;
3) There is no discharge path for C1. A high value resistor
across C2 can fix that;
4) What do expect to place across the terminals labeled 24
VDC? The voltage there may have no relation to 24 volts.

Further suggestions contingent upon knowing what is at the
24 VDC connection.

Thank you for not automatically dismissing the whole thing out of hand,
as other respondents obviously did. Not helpful.

OK, answers:

1. Yeah, it's a *drawing* error. I can still not remember which way is
which, graphically speaking, for the life of me. When I actually build
stuff I check and double-check diode anode-cathode connections, and
haven't gotten it wrong once. I guess I just need a good mnemonic to
remember which way the damn arrow points.

2. OK; I presume this needs to be the same size (power capacity) as the
resistor in series with the load, right?

3. OK.

4, 5: The load would be a small annunciator device: a doorbell, chime or
other sound-generating device, *probably* operating at 18-24 volts. I'm
guessing current draw would be in the low hundreds of mA, certainly less
than half an amp. Does that help?


-- Made From Pears: Pretty good chance that the product is at least
mostly pears. Made With Pears: Pretty good chance that pears will be
detectable in the product. Contains Pears: One pear seed per multiple
tons of product. (with apologies to Dorothy L. Sayers)

On 3/25/2009 5:24 AM David spake thus:

Actually the circuit is not all that unworkable. Some
suggestions and comments:

1) Diode D1 is backwards;
2) You need a resistor in series with D1 to limit in-rush
current;
3) There is no discharge path for C1. A high value resistor
across C2 can fix that;
4) What do expect to place across the terminals labeled 24
VDC? The voltage there may have no relation to 24 volts.

Further suggestions contingent upon knowing what is at the
24 VDC connection.

Thank you for not automatically dismissing the whole thing out of hand,
as other respondents obviously did. Not helpful.

OK, answers:

1. Yeah, it's a *drawing* error. I can still not remember which way is
which, graphically speaking, for the life of me. When I actually build
stuff I check and double-check diode anode-cathode connections, and
haven't gotten it wrong once. I guess I just need a good mnemonic to
remember which way the damn arrow points.

2. OK; I presume this needs to be the same size (power capacity) as the
resistor in series with the load, right?

3. OK.

4, 5: The load would be a small annunciator device: a doorbell, chime or
other sound-generating device, *probably* operating at 18-24 volts. I'm
guessing current draw would be in the low hundreds of mA, certainly less
than half an amp. Does that help?


--
Made From Pears: Pretty good chance that the product is at least
mostly pears.
Made With Pears: Pretty good chance that pears will be detectable in
the product.
Contains Pears: One pear seed per multiple tons of product.

(with apologies to Dorothy L. Sayers)

"David Nebenzahl" wrote in message
s.com...
On 3/25/2009 5:24 AM David spake thus:

Actually the circuit is not all that unworkable. Some
suggestions and comments:

Check the updated schematic, incorporating your
suggestions:
http://www.geocities.com/bonezphoto/...e-shotBell.gif

Let me know what you think.


--
Made From Pears: Pretty good chance that the product is at
least
mostly pears.
Made With Pears: Pretty good chance that pears will be
detectable in
the product.
Contains Pears: One pear seed per multiple tons of
product.

(with apologies to Dorothy L. Sayers)

OK the circuit is better. R3 will also discharge C2 which is
also necessary to allow the circuit to start another cycle.
The surge resistor should be in the low 10s of ohms and
probably about a watt. If the load is in the 100-200mA range
than just size the R2 resistor as needed. Remember that the
voltage across C2 will be close to 150v. I would put a Zener
diode across the load to prevent voltages going above what
your annunciate device can handle safely. Remember that this
entire circuit is at line voltage and anything connected can
be a severe shock hazard.

David

On Mar 25, 1:47*pm, David Nebenzahl wrote:

Thank you for not automatically dismissing the whole thing out of hand,
as other respondents obviously did. Not helpful.


and thank you for not multiple posting
and thank you for not multiple posting
and thank you for not multiple posting
and thank you for not multiple posting
and thank you for not multiple posting
and thank you for not multiple postilg

Further suggestions contingent upon knowing what is at the
24 VDC connection.

Thank you for not automatically dismissing the whole thing out
of hand, as other respondents obviously did. Not helpful.

What are we supposed to do? Be a free design service for someone with little
understanding of electronics?

I can see what's going to happen. You're going to build something, and when
it doesn't work, bring it back here over and over for troubleshooting
assistance.

This is not the way to learn electronics Find some books on electronics and
start reading.. Buy one of those 100-in-1 lab kits and have some fun.


Let me give a parallel example. Suppose you'd written the first chapter of a
crappy novel. Would you expect other people to guide you through the process
of editing it, and teaching you how to write, simply because they have
nothing better to do with their time?

On 3/25/2009 1:55 PM Jeff Hackler spake thus:

On Mar 25, 1:47 pm, David Nebenzahl wrote:

Thank you for not automatically dismissing the whole thing out of hand,
as other respondents obviously did. Not helpful.

and thank you for not multiple posting
and thank you for not multiple posting
and thank you for not multiple posting
and thank you for not multiple posting
and thank you for not multiple posting
and thank you for not multiple postilg

Sorry 'bout that: for some reason, my posts haven't been "getting
through" here lately (had to post the original message twice to have it
show up here at all).


--
Made From Pears: Pretty good chance that the product is at least
mostly pears.
Made With Pears: Pretty good chance that pears will be detectable in
the product.
Contains Pears: One pear seed per multiple tons of product.

(with apologies to Dorothy L. Sayers)

On 3/25/2009 10:24 AM PlainBill spake thus:

Contrary to what several nay-sayers have expressed, this exercise has
a LOT to do with electronics repair. Any fool can keep replacing
components until he finds the bad one. The successful tech will be
able to analyse a circuit and make meaningful tests to identfy the
failing part.

Thank you. It's more than a little annoying being completely written off
as a clueless idiot simply because I reversed a diode's polarity *in a
schematic* (since corrected).

NOW your next exercise is to identify the values for these components.


I'd love to oblige you; unfortunately, I'm not yet at that level. I know
Ohm's law and some other basic stuff, but not enough about circuit
design to assign values with any confidence. I look forward to others
doing that. And someday, I intend to get a good basic electronics
textbook and seriously study it ...


--
Made From Pears: Pretty good chance that the product is at least
mostly pears.
Made With Pears: Pretty good chance that pears will be detectable in
the product.
Contains Pears: One pear seed per multiple tons of product.

(with apologies to Dorothy L. Sayers)

On Wed, 25 Mar 2009 18:01:12 -0800, David Nebenzahl
wrote:

On 3/25/2009 10:24 AM PlainBill spake thus:

Contrary to what several nay-sayers have expressed, this exercise has
a LOT to do with electronics repair. Any fool can keep replacing
components until he finds the bad one. The successful tech will be
able to analyse a circuit and make meaningful tests to identfy the
failing part.

Thank you. It's more than a little annoying being completely written off
as a clueless idiot simply because I reversed a diode's polarity *in a
schematic* (since corrected).

NOW your next exercise is to identify the values for these components.


I'd love to oblige you; unfortunately, I'm not yet at that level. I know
Ohm's law and some other basic stuff, but not enough about circuit
design to assign values with any confidence. I look forward to others
doing that. And someday, I intend to get a good basic electronics
textbook and seriously study it ...

Several comments on this circuit. First of all, it could work, but
would require significant improvements, some of which have already
been discussed. Rather than using a doorbell or chime, a Sonalert
could be used. In part this will depend on the sound level desired.

Second, some of the criticisms are valid. If you intend to do this as
a design exercise you can have fun designing it, but I would not
recommend building it. You are dealing with potentially lethal
voltages, and fairly expensive components to withstand those voltages.

IMHO, you are using the wrong approach. Over 30 years ago I built
something similar using a few small caps, a few resistors, a diode, a
speaker, and a 74C914 hex schmidt trigger. I used 4 AA cells to power
it, your application should use a 'wall wart' putting out 6VDC at 100
ma. I'd have to look up the specs, but a 555 timer would also do the
job.

PlainBill

On 3/26/2009 9:21 AM PlainBill spake thus:

On Wed, 25 Mar 2009 18:01:12 -0800, David Nebenzahl
wrote:

On 3/25/2009 10:24 AM PlainBill spake thus:

Contrary to what several nay-sayers have expressed, this exercise has
a LOT to do with electronics repair. Any fool can keep replacing
components until he finds the bad one. The successful tech will be
able to analyse a circuit and make meaningful tests to identfy the
failing part.

Thank you. It's more than a little annoying being completely written off
as a clueless idiot simply because I reversed a diode's polarity *in a
schematic* (since corrected).

NOW your next exercise is to identify the values for these components.


I'd love to oblige you; unfortunately, I'm not yet at that level. I know
Ohm's law and some other basic stuff, but not enough about circuit
design to assign values with any confidence. I look forward to others
doing that. And someday, I intend to get a good basic electronics
textbook and seriously study it ...

Several comments on this circuit. First of all, it could work, but
would require significant improvements, some of which have already
been discussed. Rather than using a doorbell or chime, a Sonalert
could be used. In part this will depend on the sound level desired.

So what improvements would you suggest to the current circuit (after I
made the changes recommended earlier)? (Circuit at
http://www.geocities.com/bonezphoto/...e-shotBell.gif)

Second, some of the criticisms are valid. If you intend to do this as
a design exercise you can have fun designing it, but I would not
recommend building it. You are dealing with potentially lethal
voltages, and fairly expensive components to withstand those voltages.

To be honest, I think it's more fun designing things like this that will
operate "directly" off line voltage (i.e., without a transformer). One
of the criteria of this whole deal was to avoid the use of a transformer.

And in defense of that, there are tons of things in use every day that
operate just this way. Latest example I found were a bunch of electric
staple guns a neighbor gave me that operated directly off 120 volts,
firing a solenoid through a capacitor.

If I were to actually build this, I'm confident I could do it safely--at
least as safely as those staple guns, which have UL, CSA, etc., compliance.

And what components would be expensive? Seems to me the most expensive
part would be the transistor, or possibly the two power resistors, but
even those aren't terribly pricey.

IMHO, you are using the wrong approach. Over 30 years ago I built
something similar using a few small caps, a few resistors, a diode, a
speaker, and a 74C914 hex schmidt trigger. I used 4 AA cells to power
it, your application should use a 'wall wart' putting out 6VDC at 100
ma. I'd have to look up the specs, but a 555 timer would also do the
job.

Could do, but see above.


--
Made From Pears: Pretty good chance that the product is at least
mostly pears.
Made With Pears: Pretty good chance that pears will be detectable in
the product.
Contains Pears: One pear seed per multiple tons of product.

(with apologies to Dorothy L. Sayers)

On Mar 26, 6:12*pm, David Nebenzahl wrote:
On 3/26/2009 9:21 AM PlainBill spake thus:





On Wed, 25 Mar 2009 18:01:12 -0800, David Nebenzahl
wrote:

On 3/25/2009 10:24 AM PlainBill spake thus:

Contrary to what several nay-sayers have expressed, this exercise has
a LOT to do with electronics repair. *Any fool can keep replacing
components until he finds the bad one. *The successful tech will be
able to analyse a circuit and make meaningful tests to identfy the
failing part.

Thank you. It's more than a little annoying being completely written off
as a clueless idiot simply because I reversed a diode's polarity *in a
schematic* (since corrected).

NOW your next exercise is to identify the values for these components..


I'd love to oblige you; unfortunately, I'm not yet at that level. I know
Ohm's law and some other basic stuff, but not enough about circuit
design to assign values with any confidence. I look forward to others
doing that. And someday, I intend to get a good basic electronics
textbook and seriously study it ...

Several comments on this circuit. *First of all, it could work, but
would require significant improvements, some of which have already
been discussed. *Rather than using a doorbell or chime, a Sonalert
could be used. *In part this will depend on the sound level desired.

So what improvements would you suggest to the current circuit (after I
made the changes recommended earlier)? (Circuit athttp://www.geocities.com/bonezphoto/misc/One-shotBell.gif)

Second, some of the criticisms are valid. *If you intend to do this as
a design exercise you can have fun designing it, but I would not
recommend building it. *You are dealing with potentially lethal
voltages, and fairly expensive components to withstand those voltages.

To be honest, I think it's more fun designing things like this that will
operate "directly" off line voltage (i.e., without a transformer). One
of the criteria of this whole deal was to avoid the use of a transformer.

And in defense of that, there are tons of things in use every day that
operate just this way. Latest example I found were a bunch of electric
staple guns a neighbor gave me that operated directly off 120 volts,
firing a solenoid through a capacitor.

If I were to actually build this, I'm confident I could do it safely--at
least as safely as those staple guns, which have UL, CSA, etc., compliance.

And what components would be expensive? Seems to me the most expensive
part would be the transistor, or possibly the two power resistors, but
even those aren't terribly pricey.

IMHO, you are using the wrong approach. *Over 30 years ago I built
something similar using a few small caps, a few resistors, a diode, a
speaker, and a 74C914 hex schmidt trigger. *I used 4 AA cells to power
it, your application should use a 'wall wart' putting out 6VDC at 100
ma. *I'd have to look up the specs, but a 555 timer would also do the
job.

Could do, but see above.

--
Made From Pears: Pretty good chance that the product is at least
mostly pears.
Made With Pears: Pretty good chance that pears will be detectable in
the product.
Contains Pears: *One pear seed per multiple tons of product.

(with apologies to Dorothy L. Sayers)

And a relay won't do what you want? In theory, IF you get the
component values right AND the hot / neutral are as expected it COULD
work but I CERTAINLY would NOT allow that kind of mess in my house.

If you're going to dabble, do it at low voltages and transformer
isolated so you don't blow up stuff OR yourself.

Sorry to rain on your parade but at least you're alive to be ****ed at
me.

G²

David Nebenzahl Inscribed thus:

To be honest, I think it's more fun designing things like this that
will operate "directly" off line voltage (i.e., without a
transformer). One of the criteria of this whole deal was to avoid the
use of a transformer.

And in defense of that, there are tons of things in use every day that
operate just this way. Latest example I found were a bunch of electric
staple guns a neighbor gave me that operated directly off 120 volts,
firing a solenoid through a capacitor.

If I were to actually build this, I'm confident I could do it
safely--at least as safely as those staple guns, which have UL, CSA,
etc., compliance.

With all due respect I doubt it !

If you really look closely at the sort of products you mention, and I
could mention many more, they are all constructed in such a way that it
would be very difficult if not impossible for you to be able to touch
any part that would allow you to come into contact with the mains !

By doing what you are wanting to do, and I am not saying "Don't", you
are potentially putting yourself and others at risk of electric shock,
not to mention any other possible hazards.

I personally would want to ensure that I didn't introduce any potential
hazard that could endanger my family, myself or any visitors !

A small relay would do what you want and provide isolation from the
mains supply.

--
Best Reagrds:
Baron.

On Thu, 26 Mar 2009 17:12:00 -0800, David Nebenzahl
wrote:

On 3/26/2009 9:21 AM PlainBill spake thus:

On Wed, 25 Mar 2009 18:01:12 -0800, David Nebenzahl
wrote:

On 3/25/2009 10:24 AM PlainBill spake thus:

Contrary to what several nay-sayers have expressed, this exercise has
a LOT to do with electronics repair. Any fool can keep replacing
components until he finds the bad one. The successful tech will be
able to analyse a circuit and make meaningful tests to identfy the
failing part.

Thank you. It's more than a little annoying being completely written off
as a clueless idiot simply because I reversed a diode's polarity *in a
schematic* (since corrected).

NOW your next exercise is to identify the values for these components.


I'd love to oblige you; unfortunately, I'm not yet at that level. I know
Ohm's law and some other basic stuff, but not enough about circuit
design to assign values with any confidence. I look forward to others
doing that. And someday, I intend to get a good basic electronics
textbook and seriously study it ...

Several comments on this circuit. First of all, it could work, but
would require significant improvements, some of which have already
been discussed. Rather than using a doorbell or chime, a Sonalert
could be used. In part this will depend on the sound level desired.

So what improvements would you suggest to the current circuit (after I
made the changes recommended earlier)? (Circuit at
http://www.geocities.com/bonezphoto/...e-shotBell.gif)

You must add surge supression if you are using an inductive load.
Without it, the pulse generated when the transistor turns off will
eventually destroy it.

Second, some of the criticisms are valid. If you intend to do this as
a design exercise you can have fun designing it, but I would not
recommend building it. You are dealing with potentially lethal
voltages, and fairly expensive components to withstand those voltages.

To be honest, I think it's more fun designing things like this that will
operate "directly" off line voltage (i.e., without a transformer). One
of the criteria of this whole deal was to avoid the use of a transformer.

And in defense of that, there are tons of things in use every day that
operate just this way. Latest example I found were a bunch of electric
staple guns a neighbor gave me that operated directly off 120 volts,
firing a solenoid through a capacitor.

If I were to actually build this, I'm confident I could do it safely--at
least as safely as those staple guns, which have UL, CSA, etc., compliance.

And what components would be expensive? Seems to me the most expensive
part would be the transistor, or possibly the two power resistors, but
even those aren't terribly pricey.

Cost would depend on the nature of the load. If you are using a
Sonalert the load would be under .04A.

On the other hand, if you are using a chime the load will be higher,
and using a doorbell REALLY opens a can of worms. I think you had
better expect a load of .5A, and one heck of an inductive kick as the
transistor turns off. The typical doorbell is designed to operate on
about 15VAC. I would expect rater short contact life if you run it
off DC.


IMHO, you are using the wrong approach. Over 30 years ago I built
something similar using a few small caps, a few resistors, a diode, a
speaker, and a 74C914 hex schmidt trigger. I used 4 AA cells to power
it, your application should use a 'wall wart' putting out 6VDC at 100
ma. I'd have to look up the specs, but a 555 timer would also do the
job.

Could do, but see above.

PlainBill

In article m,
kens says...
(famous last words, "simple circuit" ...)

OK, so I'm trying to come up with a simple (maybe even elegant) solution
to a simple problem. Have an idea I want to run by y'all.

Function: person has a motion-detector light installed in their home.
They want a buzzer/bell/annunciator of some kind to go off *momentarily*
whenever the light is activated.

Here's my idea for the circuit:
http://www.geocities.com/bonezphoto/...e-shotBell.gif

First of all, please don't laugh at this. I am *not* a double-E or in
any way an electronics expert. Also keep in mind that this is the
farthest thing from a mil-spec application. It's just for fun; no life
support medical devices will depend on it.

I'd like to know the following:

1. Will this circuit even work?
1a. Will it work but end up destroying one or more components?
2. Is there a simpler way of accomplishing this task?
3. If it'll work, what are the right component values?

Explanation:

D1 is a half-wave rectifier. C2 filters the DC to produce more-or-less
ripple-free current. C1 provides the momentary "on" signal, by charging,
then "shutting down" when charged (sized according to RC time constant
to provide the desired "on" time). R2 and R3 form a voltage divider to
supply the appropriate base voltage to Q1. R1 acts as a voltage divider
in series with the load to supply the appropriate output voltage. (I
chose 24 volts DC arbitrarily; it might be less, probably not more.)

Component sizing:

R1 would obviously have to be large enough (in terms of power capacity)
to handle the load. The load would probably have a minimal current draw.
And since it would only be "on" momentarily, R1 could probably be a bit
undersized without worrying about damage.

Q1 would also need to be large enough to handle the load. I'm thinking a
common TO-220 type might work fine.

R2 & R3 could be small 1/8 watters.

OK, have at it. Rip 'er apart!



OK, so a lot of issues here deal with the AC power being detected and
transferred to something useful. I did a simple data logger for my well
pump (URL: http://personal.nbnet.nb.ca/snowowl/DataRecorder.html), that
had to deal 220V being sensed. I used a cheap little cell phone / palm
pilot charger that was universal 110/220 50/60hz and wired it parallel
with the motor leads. This gave me a nice 5 volts when the power was
applied to the pump, so I could log it's on cycles. You still have to
wire it up the the light, so that's a danger here as well. Dealing with
AC mains wiring, there always a need for extra safety.

- Tim -

On 3/27/2009 3:55 PM Tim spake thus:

In article m,
kens says...

(famous last words, "simple circuit" ...)

OK, so I'm trying to come up with a simple (maybe even elegant) solution
to a simple problem. Have an idea I want to run by y'all.

Function: person has a motion-detector light installed in their home.
They want a buzzer/bell/annunciator of some kind to go off *momentarily*
whenever the light is activated.

Here's my idea for the circuit:
http://www.geocities.com/bonezphoto/...e-shotBell.gif

OK, so a lot of issues here deal with the AC power being detected and
transferred to something useful. I did a simple data logger for my well
pump (URL: http://personal.nbnet.nb.ca/snowowl/DataRecorder.html), that
had to deal 220V being sensed. I used a cheap little cell phone / palm
pilot charger that was universal 110/220 50/60hz and wired it parallel
with the motor leads. This gave me a nice 5 volts when the power was
applied to the pump, so I could log it's on cycles. You still have to
wire it up the the light, so that's a danger here as well. Dealing with
AC mains wiring, there always a need for extra safety.

Thanks for your reply.

Unfortunately, your solution, while interesting, misses one of the
requirements of the whole deal: it needs to operate the
bell/chime/annunciator *momentarily*, not continuously.


--
Made From Pears: Pretty good chance that the product is at least
mostly pears.
Made With Pears: Pretty good chance that pears will be detectable in
the product.
Contains Pears: One pear seed per multiple tons of product.

(with apologies to Dorothy L. Sayers)

"David Nebenzahl" wrote in message
s.com...
On 3/27/2009 3:55 PM Tim spake thus:

OK, so I'm trying to come up with a simple (maybe even
elegant) solution to a simple problem. Have an idea I
want to run by y'all.

Function: person has a motion-detector light installed
in their home. They want a buzzer/bell/annunciator of
some kind to go off *momentarily* whenever the light is
activated.

Here's my idea for the circuit:
http://www.geocities.com/bonezphoto/...e-shotBell.gif

OK, so a lot of issues here deal with the AC power being
detected and transferred to something useful. I did a
simple data logger for my well pump (URL:
http://personal.nbnet.nb.ca/snowowl/DataRecorder.html),
that had to deal 220V being sensed. I used a cheap little
cell phone / palm pilot charger that was universal
110/220 50/60hz and wired it parallel with the motor
leads. This gave me a nice 5 volts when the power was
applied to the pump, so I could log it's on cycles. You
still have to wire it up the the light, so that's a
danger here as well. Dealing with AC mains wiring, there
always a need for extra safety.

Thanks for your reply.

Unfortunately, your solution, while interesting, misses
one of the requirements of the whole deal: it needs to
operate the bell/chime/annunciator *momentarily*, not
continuously.

Why not take a crack at calculating the values of the
components and post your final circuit here. That way we
will get a good idea of how adept you are at circuit design.
I would still recommend putting R3 across C2 rather than C1
as per my original suggestion. That insures the drive to the
transistor truly goes to zero after some amount of time.

David

David Nebenzahl wrote:

On 3/27/2009 3:55 PM Tim spake thus:

In article m,
kens says...

(famous last words, "simple circuit" ...)

OK, so I'm trying to come up with a simple (maybe even elegant)
solution to a simple problem. Have an idea I want to run by y'all.

Function: person has a motion-detector light installed in their
home. They want a buzzer/bell/annunciator of some kind to go off
*momentarily* whenever the light is activated.

I think that a small sugar cube relay, diode, resistor and capacitor
will do the job !

--
Best Regards:
Baron.

On 3/28/2009 1:30 PM Baron spake thus:

David Nebenzahl wrote:

On 3/27/2009 3:55 PM Tim spake thus:

In article m,
kens says...

(famous last words, "simple circuit" ...)

OK, so I'm trying to come up with a simple (maybe even elegant)
solution to a simple problem. Have an idea I want to run by y'all.

Function: person has a motion-detector light installed in their
home. They want a buzzer/bell/annunciator of some kind to go off
*momentarily* whenever the light is activated.

I think that a small sugar cube relay, diode, resistor and capacitor
will do the job !

Circuit, pleeze?


--
Made From Pears: Pretty good chance that the product is at least
mostly pears.
Made With Pears: Pretty good chance that pears will be detectable in
the product.
Contains Pears: One pear seed per multiple tons of product.

(with apologies to Dorothy L. Sayers)

On 3/28/2009 12:26 PM David spake thus:

"David Nebenzahl" wrote in message
s.com...

OK, so I'm trying to come up with a simple (maybe even
elegant) solution to a simple problem. Have an idea I
want to run by y'all.

Function: person has a motion-detector light installed
in their home. They want a buzzer/bell/annunciator of
some kind to go off *momentarily* whenever the light is
activated.

Here's my idea for the circuit:
http://www.geocities.com/bonezphoto/...e-shotBell.gif

Why not take a crack at calculating the values of the
components and post your final circuit here. That way we
will get a good idea of how adept you are at circuit design.
I would still recommend putting R3 across C2 rather than C1
as per my original suggestion. That insures the drive to the
transistor truly goes to zero after some amount of time.

Hey, thanks for sticking with me. Check latest circuit incarnation at
http://www.geocities.com/bonezphoto/...e-shotBell.gif.

Component Value
-----------------------------
C1 100 uf/200 V.
C2 1 uf/100 V.
R1, R2 500 Ω, 2 W
R3 220 kΩ, 1/8 W
R4, R5 10 kΩ, 1/8 W
D1 1N4001
Q1 D1266 or equiv.

Rationale for values (assuming ~20 volt, 100 mA load):

C1: large enough to filter bulk of ripple
C2: sized for proper "on" time (WAG)
R1, R2: voltage divider to yield ~20 volts for load device;
calculations dictate 5 watt load, but since it's of short
duration, 2 w. should be sufficient
R3: bleeder (slow) for C1
R4, R5: this is also a WAG (wild-ass guess); see below
D1: 1A, 600 PIV
Q1: selected because I have these and have used them before.

OK, I admit that I do not know how to calculate those last 2 resistances
for proper biasing of Q1; so sue me. I do understanfd the general
principle of biasing; just never had the formal training to learn how to
calculate values to implement it. I'd appreciate your comments here, and
I'd be curious to know how far off my guesses were.

BTW, I misunderstood where you wanted the bleeder resistor.

So give me a grade on my work.


--
Made From Pears: Pretty good chance that the product is at least
mostly pears.
Made With Pears: Pretty good chance that pears will be detectable in
the product.
Contains Pears: One pear seed per multiple tons of product.

(with apologies to Dorothy L. Sayers)

On Sat, 28 Mar 2009 11:00:45 -0800, David Nebenzahl
wrote:

On 3/27/2009 3:55 PM Tim spake thus:

In article m,
kens says...

(famous last words, "simple circuit" ...)

OK, so I'm trying to come up with a simple (maybe even elegant) solution
to a simple problem. Have an idea I want to run by y'all.

Function: person has a motion-detector light installed in their home.
They want a buzzer/bell/annunciator of some kind to go off *momentarily*
whenever the light is activated.

Here's my idea for the circuit:
http://www.geocities.com/bonezphoto/...e-shotBell.gif

OK, so a lot of issues here deal with the AC power being detected and
transferred to something useful. I did a simple data logger for my well
pump (URL: http://personal.nbnet.nb.ca/snowowl/DataRecorder.html), that
had to deal 220V being sensed. I used a cheap little cell phone / palm
pilot charger that was universal 110/220 50/60hz and wired it parallel
with the motor leads. This gave me a nice 5 volts when the power was
applied to the pump, so I could log it's on cycles. You still have to
wire it up the the light, so that's a danger here as well. Dealing with
AC mains wiring, there always a need for extra safety.

Thanks for your reply.

Unfortunately, your solution, while interesting, misses one of the
requirements of the whole deal: it needs to operate the
bell/chime/annunciator *momentarily*, not continuously.


Since you need 18-24vdc, instead of the hazard of components
directly connected to the powerline, use an approved AC adapter or
"wallwart" that would provide the necessary DC voltage. From the
output of the AC adapter, place a PTC (positive temperature
coefficient) thermistor in series with your load. It will be a bit
tricky to determine the right physical size and nominal resistance of
the thermistor, since you haven't specified the load.
When the adapter powers up, the thermistor will be cold, and will
run the "indicator" what ever that is. After the thermistor heats up,
it will reduce the current going to your device, hopefully to the
point where it won't be noticed. The "resetable fuses" work on this
idea, you could use one of them the same way, but you need to again
select based on current load, and power.
If you get it to work it's: simple
doesn't violate electrical safety
reliable
The disadvantage, is that once on, it needs some time to "reset"
(cool down). The thermistor does get hot, a poorly designed circuit
could get hot enough to be a problem.

There are relay circuits that do much the same, but I'd run them
off the ac adapter as well. (relay in series with large cap, operates
when cap charges up. cap was bleeder resistor in parallel so it
discharges prperly when power is removed). The relay circuit would be
straight forward to calculate the on time (a percentage of the time
constant).

I'd prefer you stick to quite low voltages (6-12v), to minimize any
risk of shock. Who knows how this circuit might be physically
implemented!

Paul G.

"David Nebenzahl" wrote in message
s.com...
On 3/28/2009 12:26 PM David spake thus:

"David Nebenzahl" wrote in
message
s.com...

OK, so I'm trying to come up with a simple (maybe even
elegant) solution to a simple problem. Have an idea I
want to run by y'all.

Function: person has a motion-detector light
installed in their home. They want a
buzzer/bell/annunciator of some kind to go off
*momentarily* whenever the light is activated.

Here's my idea for the circuit:
http://www.geocities.com/bonezphoto/...e-shotBell.gif

Why not take a crack at calculating the values of the
components and post your final circuit here. That way we
will get a good idea of how adept you are at circuit
design. I would still recommend putting R3 across C2
rather than C1 as per my original suggestion. That
insures the drive to the transistor truly goes to zero
after some amount of time.

Hey, thanks for sticking with me. Check latest circuit
incarnation at
http://www.geocities.com/bonezphoto/...e-shotBell.gif.

Component Value
-----------------------------
C1 100 uf/200 V.
C2 1 uf/100 V.
R1, R2 500 Ω, 2 W
R3 220 kΩ, 1/8 W
R4, R5 10 kΩ, 1/8 W
D1 1N4001
Q1 D1266 or equiv.

Rationale for values (assuming ~20 volt, 100 mA load):

C1: large enough to filter bulk of ripple
C2: sized for proper "on" time (WAG)
R1, R2: voltage divider to yield ~20 volts for load
device;
calculations dictate 5 watt load, but since it's
of short
duration, 2 w. should be sufficient
R3: bleeder (slow) for C1
R4, R5: this is also a WAG (wild-ass guess); see below
D1: 1A, 600 PIV
Q1: selected because I have these and have used them
before.

OK, I admit that I do not know how to calculate those last
2 resistances for proper biasing of Q1; so sue me. I do
understanfd the general principle of biasing; just never
had the formal training to learn how to calculate values
to implement it. I'd appreciate your comments here, and
I'd be curious to know how far off my guesses were.

BTW, I misunderstood where you wanted the bleeder
resistor.

So give me a grade on my work.

So far the grade is not very good. The transistor is rated
at 60v. When the transistor is off it has to sustain the
full rectified voltage.of about 150v. The same is true of
C2. R3 is still in the wrong place. R5 should be much
smaller than R4 since Vbe will always be under a volt. R1,
R2 are close, but how sure are you that 20v will not
destroy the load? A better choice would be a smaller R1 and
larger R2 since the circuit as shown introduces a lot of C
to B feedback which will drastically slow down the turnoff
time and keep the transistor in a linear mode for longer
than necessary. Need load on time, and hfe of the transistor
you choose to calculate C2, R4, and R5.

Other prople replying have suggested either a transformer
isolated design or the use of a small relay and a simple
diode RC network to drive it. The relay is a good choice if
you can get the power to run the load elsewhere.

David

Just one small question: earlier, you said:

... I would still recommend putting R3 across C2
rather than C1 as per my original suggestion. That
insures the drive to the transistor truly goes to zero
after some amount of time.

So I thought I did that. But then you said:

R3 is still in the wrong place.

So what's the right place? I've put it across both caps and you still
don't seem to be happy.


--
Made From Pears: Pretty good chance that the product is at least
mostly pears.
Made With Pears: Pretty good chance that pears will be detectable in
the product.
Contains Pears: One pear seed per multiple tons of product.

(with apologies to Dorothy L. Sayers)

David Nebenzahl wrote:

On 3/28/2009 1:30 PM Baron spake thus:

David Nebenzahl wrote:

On 3/27/2009 3:55 PM Tim spake thus:

In article m,
kens says...

(famous last words, "simple circuit" ...)

OK, so I'm trying to come up with a simple (maybe even elegant)
solution to a simple problem. Have an idea I want to run by y'all.

Function: person has a motion-detector light installed in their
home. They want a buzzer/bell/annunciator of some kind to go off
*momentarily* whenever the light is activated.

I think that a small sugar cube relay, diode, resistor and capacitor
will do the job !

Circuit, pleeze?


Ok but excuse the ascii art.

live ----diode---relay---resistor---capacitor---neutral

Size the resistor to give the time constant with a particular value
capacitor. The relay contacts are isolated and can be connected to
your low voltage circuit.

The resistor should have sufficient wattage rating with respect to the
current and the capacitor should be rated for at least the maximum
voltage applied. ie 120v X 1.414. The relay can be almost anything
with a suitable coil voltage. ie 100 - 120.

The circuit works by utilising the charging current into the capacitor
to energise the relay. As the capacitor voltage increases the relay
will drop out. The time difference between energising and dropping out
is how long the annunciator will sound.

--
Best Regards:
Baron.

In article m,
kens says...
On 3/27/2009 3:55 PM Tim spake thus:

In article m,
kens says...

(famous last words, "simple circuit" ...)

OK, so I'm trying to come up with a simple (maybe even elegant) solution
to a simple problem. Have an idea I want to run by y'all.

Function: person has a motion-detector light installed in their home.
They want a buzzer/bell/annunciator of some kind to go off *momentarily*
whenever the light is activated.

Here's my idea for the circuit:
http://www.geocities.com/bonezphoto/...e-shotBell.gif

OK, so a lot of issues here deal with the AC power being detected and
transferred to something useful. I did a simple data logger for my well
pump (URL: http://personal.nbnet.nb.ca/snowowl/DataRecorder.html), that
had to deal 220V being sensed. I used a cheap little cell phone / palm
pilot charger that was universal 110/220 50/60hz and wired it parallel
with the motor leads. This gave me a nice 5 volts when the power was
applied to the pump, so I could log it's on cycles. You still have to
wire it up the the light, so that's a danger here as well. Dealing with
AC mains wiring, there always a need for extra safety.

Thanks for your reply.

Unfortunately, your solution, while interesting, misses one of the
requirements of the whole deal: it needs to operate the
bell/chime/annunciator *momentarily*, not continuously.



Perhaps you are not inventive enough. My idea was to get a voltage low
enough to be safe. 5 volts could be used to fire a simple one-shot
circuit when the light comes on.

- Tim -

On 3/29/2009 6:43 AM Baron spake thus:

David Nebenzahl wrote:

On 3/28/2009 1:30 PM Baron spake thus:

David Nebenzahl wrote:

On 3/27/2009 3:55 PM Tim spake thus:

In article m,
kens says...

(famous last words, "simple circuit" ...)

OK, so I'm trying to come up with a simple (maybe even elegant)
solution to a simple problem. Have an idea I want to run by y'all.

Function: person has a motion-detector light installed in their
home. They want a buzzer/bell/annunciator of some kind to go off
*momentarily* whenever the light is activated.

I think that a small sugar cube relay, diode, resistor and capacitor
will do the job !

Circuit, pleeze?

Ok but excuse the ascii art.

live ----diode---relay---resistor---capacitor---neutral

You're excused. That illustrates the circuit perfectly.

Size the resistor to give the time constant with a particular value
capacitor. The relay contacts are isolated and can be connected to
your low voltage circuit.

The resistor should have sufficient wattage rating with respect to the
current and the capacitor should be rated for at least the maximum
voltage applied. ie 120v X 1.414. The relay can be almost anything
with a suitable coil voltage. ie 100 - 120.

The circuit works by utilising the charging current into the capacitor
to energise the relay. As the capacitor voltage increases the relay
will drop out. The time difference between energising and dropping out
is how long the annunciator will sound.

So I take it you'd like this circuit:
http://www.geocities.com/bonezphoto/...-shotBell2.gif

And now can you give us the R and C values to give, say, a 1- or
2-second on time? I don't know how to calculate such things. (Understand
how they work, just never learned the actual math involved.)


--
Made From Pears: Pretty good chance that the product is at least
mostly pears.
Made With Pears: Pretty good chance that pears will be detectable in
the product.
Contains Pears: One pear seed per multiple tons of product.

(with apologies to Dorothy L. Sayers)

David Nebenzahl wrote:
I'd love to oblige you; unfortunately, I'm not yet at that level. I know
Ohm's law and some other basic stuff, but not enough about circuit
design to assign values with any confidence. I look forward to others
doing that. And someday, I intend to get a good basic electronics
textbook and seriously study it ...

"The Art of Electronics" by Horowitz & Hill. You'll save a fortune if
you buy a used student copy.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------

David Nebenzahl wrote:

On 3/29/2009 6:43 AM Baron spake thus:

David Nebenzahl wrote:

On 3/28/2009 1:30 PM Baron spake thus:

David Nebenzahl wrote:

On 3/27/2009 3:55 PM Tim spake thus:

In article m,
kens says...

(famous last words, "simple circuit" ...)

OK, so I'm trying to come up with a simple (maybe even elegant)
solution to a simple problem. Have an idea I want to run by
y'all.

Function: person has a motion-detector light installed in their
home. They want a buzzer/bell/annunciator of some kind to go off
*momentarily* whenever the light is activated.

I think that a small sugar cube relay, diode, resistor and
capacitor will do the job !

Circuit, pleeze?

Ok but excuse the ascii art.

live ----diode---relay---resistor---capacitor---neutral

You're excused. That illustrates the circuit perfectly.

Size the resistor to give the time constant with a particular value
capacitor. The relay contacts are isolated and can be connected to
your low voltage circuit.

The resistor should have sufficient wattage rating with respect to
the current and the capacitor should be rated for at least the
maximum voltage applied. ie 120v X 1.414. The relay can be almost
anything with a suitable coil voltage. ie 100 - 120.

The circuit works by utilising the charging current into the
capacitor to energise the relay. As the capacitor voltage increases
the relay will drop out. The time difference between energising and
dropping out is how long the annunciator will sound.

So I take it you'd like this circuit:
http://www.geocities.com/bonezphoto/...-shotBell2.gif

That is just about it ! I hadn't considered connecting the relay
contacts back to the source to feed a transformer, but yes and the
transformer provides the safety isolation.

And now can you give us the R and C values to give, say, a 1- or
2-second on time? I don't know how to calculate such things.
(Understand how they work, just never learned the actual math
involved.)

Mmm, I tend to have trouble with decimal points. :-)

Thats a little more difficult ! You need to know the characteristics of
the relay you are going to use.

For example: If the relay requires 0.01 amp (10ma)at 90 volts to pull
in. That would give a 90/0.01 = 9K Coil resistance.

Since the capacitor will be fully discharged initially the current to
charge it up will be limited by the resistance of the relay plus R. So
in this example there may be enough time constant due to the relay
itself if the capacitor value is well chosen.

The time is basically 63% of R X C Seconds.

Lets try 100uf @ 160vwg. 0.0001F X 9000 = 0.9 Seconds /100 X 63 = 0.56.
About half a second. So for this example a 220uf @ 160vwg would be
about 1 second.

Since the current for the relay to drop out will be less than than 0.01a
the time will be less than this.

I would actually measure the relay I was going to use and adjust values
to suit. I'm sure you get the idea...

--
Best Regards:
Baron.

"David Nebenzahl" wrote in message
s.com...
On 3/29/2009 6:43 AM Baron spake thus:

David Nebenzahl wrote:
Ok but excuse the ascii art.

live ----diode---relay---resistor---capacitor---neutral

You're excused. That illustrates the circuit perfectly.

Size the resistor to give the time constant with a
particular value
capacitor. The relay contacts are isolated and can be
connected to
your low voltage circuit.

The resistor should have sufficient wattage rating with
respect to the
current and the capacitor should be rated for at least
the maximum
voltage applied. ie 120v X 1.414. The relay can be
almost anything
with a suitable coil voltage. ie 100 - 120.

The circuit works by utilising the charging current into
the capacitor
to energise the relay. As the capacitor voltage
increases the relay
will drop out. The time difference between energising
and dropping out
is how long the annunciator will sound.

So I take it you'd like this circuit:
http://www.geocities.com/bonezphoto/...-shotBell2.gif

And now can you give us the R and C values to give, say, a
1- or 2-second on time? I don't know how to calculate such
things. (Understand how they work, just never learned the
actual math involved.)

I thought you learned that there should be a discharge path
for the capacitor unless you want to wait hours or days
before it will work a second time.

David

"David" wrote in message
...

"David Nebenzahl" wrote in
message
s.com...
On 3/29/2009 6:43 AM Baron spake thus:

David Nebenzahl wrote:
Ok but excuse the ascii art.

live ----diode---relay---resistor---capacitor---neutral

You're excused. That illustrates the circuit perfectly.

Size the resistor to give the time constant with a
particular value
capacitor. The relay contacts are isolated and can be
connected to
your low voltage circuit.

The resistor should have sufficient wattage rating with
respect to the
current and the capacitor should be rated for at least
the maximum
voltage applied. ie 120v X 1.414. The relay can be
almost anything
with a suitable coil voltage. ie 100 - 120.

The circuit works by utilising the charging current into
the capacitor
to energise the relay. As the capacitor voltage
increases the relay
will drop out. The time difference between energising
and dropping out
is how long the annunciator will sound.

So I take it you'd like this circuit:
http://www.geocities.com/bonezphoto/...-shotBell2.gif

And now can you give us the R and C values to give, say,
a 1- or 2-second on time? I don't know how to calculate
such things. (Understand how they work, just never
learned the actual math involved.)

I thought you learned that there should be a discharge
path for the capacitor unless you want to wait hours or
days before it will work a second time.

David

Following up on my own post, the circuit is poor for other
reasons. Think about what happens on the negative half
cycles of the AC input. You need at least a 'catch' diode in
there.

David

David wrote:


"David Nebenzahl" wrote in message
s.com...
On 3/29/2009 6:43 AM Baron spake thus:

David Nebenzahl wrote:
Ok but excuse the ascii art.

live ----diode---relay---resistor---capacitor---neutral

You're excused. That illustrates the circuit perfectly.

Size the resistor to give the time constant with a
particular value
capacitor. The relay contacts are isolated and can be
connected to
your low voltage circuit.

The resistor should have sufficient wattage rating with
respect to the
current and the capacitor should be rated for at least
the maximum
voltage applied. ie 120v X 1.414. The relay can be
almost anything
with a suitable coil voltage. ie 100 - 120.

The circuit works by utilising the charging current into
the capacitor
to energise the relay. As the capacitor voltage
increases the relay
will drop out. The time difference between energising
and dropping out
is how long the annunciator will sound.

So I take it you'd like this circuit:
http://www.geocities.com/bonezphoto/...-shotBell2.gif

And now can you give us the R and C values to give, say, a
1- or 2-second on time? I don't know how to calculate such
things. (Understand how they work, just never learned the
actual math involved.)

I thought you learned that there should be a discharge path
for the capacitor unless you want to wait hours or days
before it will work a second time.

David

Sorry my error I forgot to put one in :-(
You need to bleed about 1/10th of the relay current.
It should go directly across the cap.

--
Best Regards:
Baron.

On 3/30/2009 5:01 AM David spake thus:

Following up on my own post, the circuit is poor for other
reasons. Think about what happens on the negative half
cycles of the AC input. You need at least a 'catch' diode in
there.

OK, I take your previous point about having a bleeder resistor to
discharge the cap.

I fail to understand why "negative half cycles of the AC input" are any
kind of a problem. Isn't that the very function of a rectifier? The
1N4001, f'rinstance, is rated at 600 PIV, so what's the problem? The
negative half cycles are simply blocked by the diode, right?

Just out of curiosity, what's a "catch diode"?


--
Made From Pears: Pretty good chance that the product is at least
mostly pears.
Made With Pears: Pretty good chance that pears will be detectable in
the product.
Contains Pears: One pear seed per multiple tons of product.

(with apologies to Dorothy L. Sayers)

David wrote:


"David Nebenzahl" wrote in message
s.com...
On 3/29/2009 6:43 AM Baron spake thus:

David Nebenzahl wrote:
Ok but excuse the ascii art.

live ----diode---relay---resistor---capacitor---neutral

You're excused. That illustrates the circuit perfectly.

Size the resistor to give the time constant with a
particular value
capacitor. The relay contacts are isolated and can be
connected to
your low voltage circuit.

The resistor should have sufficient wattage rating with
respect to the
current and the capacitor should be rated for at least
the maximum
voltage applied. ie 120v X 1.414. The relay can be
almost anything
with a suitable coil voltage. ie 100 - 120.

The circuit works by utilising the charging current into
the capacitor
to energise the relay. As the capacitor voltage
increases the relay
will drop out. The time difference between energising
and dropping out
is how long the annunciator will sound.

So I take it you'd like this circuit:
http://www.geocities.com/bonezphoto/...-shotBell2.gif

And now can you give us the R and C values to give, say, a
1- or 2-second on time? I don't know how to calculate such
things. (Understand how they work, just never learned the
actual math involved.)

I thought you learned that there should be a discharge path
for the capacitor unless you want to wait hours or days
before it will work a second time.

David

Yes you're right !
Sorry my error I forgot to put one in Â*:-(
You need to bleed about 1/10th of the relay current.
It should go directly across the cap.

--
Best Regards:
Baron.