I'm involved in a small project which needs to respond to the output
from a photodiode.

A Maplin L67BQ power adapter provides the 9v needed to power a LED
which then reflects via a moving mirror to activated the photodiode,
which in turn provides 9v.

This works fine but the signal has to be taken over about 30m and into
a computer adapter which should detect the voltage but doesn't.

On checking, the Maplin adapter appears to be isolated from mains
earth and neutral. So I can register the 9v between signal and the
adapter neutral but not between signal and mains neutral.

I assume the computer is checking the voltage with reference to it's
own neutral, which would be power supply neutral or signal ground.

How do I get round this?

Thanks

--
AnthonyL

AnthonyL wrote:
I'm involved in a small project which needs to respond to the output
from a photodiode.

A Maplin L67BQ power adapter provides the 9v needed to power a LED
which then reflects via a moving mirror to activated the photodiode,
which in turn provides 9v.

This works fine but the signal has to be taken over about 30m and into
a computer adapter which should detect the voltage but doesn't.

On checking, the Maplin adapter appears to be isolated from mains
earth and neutral. So I can register the 9v between signal and the
adapter neutral but not between signal and mains neutral.

I assume the computer is checking the voltage with reference to it's
own neutral, which would be power supply neutral or signal ground.

How do I get round this?


I think understanding electronics would be a start.

I do, and none of the above makes sense..

1/. What has the Maplin PSU got to do with the photdiode output whih is
entirely independent and separate.?

2/. What is it 'in(to) the computer' that measures voltage? Nothing in
my computer measures voltage apart from a few embedded sensors, and they
don't get to the outside world.




Thanks

On Tue, 15 Nov 2011 14:43:16 GMT, lid (AnthonyL) wrote:

I'm involved in a small project which needs to respond to the output
from a photodiode.

A Maplin L67BQ power adapter provides the 9v needed to power a LED
which then reflects via a moving mirror to activated the photodiode,
which in turn provides 9v.

You'll only get a maximum of 0.6V or so from a photodiode, not 9V. This 0.6V is relative
to the diode's anode and cathode, nothing else.


--
Regards, Paul Herber, Sandrila Ltd.
Electronics for Visio http://www.sandrila.co.uk/visio-electronics/
Electrical for Visio http://www.sandrila.co.uk/visio-electrical/
Electronics Packages for Visio http://www.sandrila.co.uk/visio-electronics-packages/

AnthonyL wrote:
I'm involved in a small project which needs to respond to the output
from a photodiode.

A Maplin L67BQ power adapter provides the 9v needed to power a LED
which then reflects via a moving mirror to activated the photodiode,
which in turn provides 9v.

This works fine but the signal has to be taken over about 30m and into
a computer adapter which should detect the voltage but doesn't.

On checking, the Maplin adapter appears to be isolated from mains
earth and neutral. So I can register the 9v between signal and the
adapter neutral but not between signal and mains neutral.

I assume the computer is checking the voltage with reference to it's
own neutral, which would be power supply neutral or signal ground.

Are you using two wire cores to take the signal from the LED/ photodiode
module to the computer or one? As described, your LED/ photodiode system
may be floating with respect to the computer input, so will not register
a voltage.

If you're not using two cores for the interconnect, then you should be.
You can't rely on using mains neutral as a return in any system of this
sort.

When you put a meter across the input to the computer module at the
computer end of the cable, do you get a clean 9 volt reading?

It is also possible, but unlikely, that you're picking up mains
interference which is causing the fault. You may need to use shielded
cable, depending on the circuit impedances.
--
Tciao for Now!

John.

Paul Herber wrote:
On Tue, 15 Nov 2011 14:43:16 GMT, lid (AnthonyL) wrote:

I'm involved in a small project which needs to respond to the output
from a photodiode.
A Maplin L67BQ power adapter provides the 9v needed to power a LED
which then reflects via a moving mirror to activated the photodiode,
which in turn provides 9v.

You'll only get a maximum of 0.6V or so from a photodiode, not 9V. This 0.6V is relative
to the diode's anode and cathode, nothing else.


+1.

Need an opamp to boost that a bit.LM724 is good.


Or some of them can be used reverse biased FROM a 9v supply with a
resistor in series..when illuminated they leak like a wimpey home.And
the voltage drops..

"AnthonyL" wrote in message
...
I'm involved in a small project which needs to respond to the output
from a photodiode.

A Maplin L67BQ power adapter provides the 9v needed to power a LED
which then reflects via a moving mirror to activated the photodiode,
which in turn provides 9v.

This works fine but the signal has to be taken over about 30m and into
a computer adapter which should detect the voltage but doesn't.

On checking, the Maplin adapter appears to be isolated from mains
earth and neutral. So I can register the 9v between signal and the
adapter neutral but not between signal and mains neutral.

I assume the computer is checking the voltage with reference to it's
own neutral, which would be power supply neutral or signal ground.

How do I get round this?

Thanks

--
AnthonyL

Hi Ant.
What Computer Adaptor are you using and do you have the drivers for it?
Baz.

On Tue, 15 Nov 2011 14:43:16 +0000, AnthonyL wrote:
A Maplin L67BQ power adapter provides the 9v needed to power a LED which
then reflects via a moving mirror to activated the photodiode, which in
turn provides 9v.

This works fine

Just to be clear, you have a power supply, LED, mirror, and *something*
(I suspect not a photodiode - or at least not in isolation) which is
putting out +9V with respect to the power supply's ground when the light
falls on it?

but the signal has to be taken over about 30m and into a
computer adapter which should detect the voltage but doesn't.

What is this computer adapter?

If you're feeding +9V into an old PC parallel port, you'll probably break
something (they're only designed for TTL levels).

If you're using one of the lines on a serial port, that'll probably work
(although some PCs can be a bit picky, so I'm not sure that +9V is
guaranteed to work despite what the spec might say).

But "computer adapter" could mean all manner of things...

On checking, the Maplin adapter appears to be isolated from mains earth
and neutral.

That confuses me. Typically these "wall wart" supplies are plastic-cased
and have no earth, true - but they'll still be connected to live and
neutral on the AC side; they won't work otherwise.

So I can register the 9v between signal and the adapter
neutral but not between signal and mains neutral.

You're not running a single wire back from the detector to the computer,
are you? You need to connect ground on the computer to ground on the
detector (and forget about anything to do with "neutral" or the mains AC
side of either the computer or the Maplin supply)

30m is quite a distance, too; using good quality shielded cable is
probably a must...

cheers

Jules

"AnthonyL" wrote in message
...
I'm involved in a small project which needs to respond to the output
from a photodiode.

A Maplin L67BQ power adapter provides the 9v needed to power a LED
which then reflects via a moving mirror to activated the photodiode,
which in turn provides 9v.

This works fine but the signal has to be taken over about 30m and into
a computer adapter which should detect the voltage but doesn't.

On checking, the Maplin adapter appears to be isolated from mains
earth and neutral. So I can register the 9v between signal and the
adapter neutral but not between signal and mains neutral.

I assume the computer is checking the voltage with reference to it's
own neutral, which would be power supply neutral or signal ground.

How do I get round this?

Thanks

Sorry if I'm being dumb here, but are you only providing a single wire to
the PC and expecting the PC to measure this relative to some floating datum?

On 15/11/2011 14:43, AnthonyL wrote:
I'm involved in a small project which needs to respond to the output
from a photodiode.

A Maplin L67BQ power adapter provides the 9v needed to power a LED

The LED lifetime on 9v will be exceedingly short unless there is a
current limiting resistor in series with it - depending on the colour an
LED will drop anything between 2v (red) to 4v (blue & white).

which then reflects via a moving mirror to activated the photodiode,
which in turn provides 9v.

This seems unlikely. The signal might be a few volts at negligible
current depending on how you wire it up with a series resistance and how
well the detector is screened from ambient light and filtered. It will
not travel well down a long cable though...

This works fine but the signal has to be taken over about 30m and into
a computer adapter which should detect the voltage but doesn't.

Test it with a shorter cable. What you say doesn't make a lot of sense.
you seem to be complaining that the Maplin PSU is floating wrt mains
earth (which seems quite likely). You just have to run a pair of cables
or better a screened signal cable with earth on the screen to the PC.

On checking, the Maplin adapter appears to be isolated from mains
earth and neutral. So I can register the 9v between signal and the
adapter neutral but not between signal and mains neutral.

I assume the computer is checking the voltage with reference to it's
own neutral, which would be power supply neutral or signal ground.

How do I get round this?

You probably need to buffer the photodiode with an opamp so that it can
drive the cable to the PC with suitable signal levels and frequency
response. How are you measuring it at the PC end? Line in ?

You would probably be better off asking on sci.electronics.basics

Daqarta will give you a quick realtime display of the audio in channels.

--
Regards,
Martin Brown

On 15/11/2011 15:12, Jules Richardson wrote:
On Tue, 15 Nov 2011 14:43:16 +0000, AnthonyL wrote:
A Maplin L67BQ power adapter provides the 9v needed to power a LED which
then reflects via a moving mirror to activated the photodiode, which in
turn provides 9v.

This works fine

Just to be clear, you have a power supply, LED, mirror, and *something*
(I suspect not a photodiode - or at least not in isolation) which is
putting out +9V with respect to the power supply's ground when the light
falls on it?

but the signal has to be taken over about 30m and into a
computer adapter which should detect the voltage but doesn't.

What is this computer adapter?

If you're feeding +9V into an old PC parallel port, you'll probably break
something (they're only designed for TTL levels).

If you're using one of the lines on a serial port, that'll probably work
(although some PCs can be a bit picky, so I'm not sure that +9V is
guaranteed to work despite what the spec might say).

9V is well in spec for RS232C which is what a traditional PC serial port
works to, however it only reads digital levels, and does not perform
analogue to digital conversion as such. Fine if all you need is an
illuminated, not illuminated indication - not much use for an indication
of the level of illumination.

(a standard joystick port can do A to D if you scale the voltage a bit
first)


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

John Rumm wrote:

a standard joystick port can do A to D if you scale the voltage a bit
first

When was the last time you saw a PC with a joystick port?

"AnthonyL" wrote in message
...
I'm involved in a small project which needs to respond to the output
from a photodiode.

A Maplin L67BQ power adapter provides the 9v needed to power a LED
which then reflects via a moving mirror to activated the photodiode,
which in turn provides 9v.

This works fine but the signal has to be taken over about 30m and into
a computer adapter which should detect the voltage but doesn't.

On checking, the Maplin adapter appears to be isolated from mains
earth and neutral. So I can register the 9v between signal and the
adapter neutral but not between signal and mains neutral.

I assume the computer is checking the voltage with reference to it's
own neutral, which would be power supply neutral or signal ground.

How do I get round this?

Buy one of these http://www.maplin.co.uk/mk120-ir-bea...detector-27513
and modify as required.

On 15/11/2011 17:32, Andy Burns wrote:
John Rumm wrote:

a standard joystick port can do A to D if you scale the voltage a bit
first

When was the last time you saw a PC with a joystick port?

glances to his left about a second ago...

(you can also do analogue input on the line in - but even more
restrictive on range)


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

John Rumm wrote:

On 15/11/2011 17:32, Andy Burns wrote:

When was the last time you saw a PC with a joystick port?

glances to his left about a second ago...

Yeah, I was half-expecting that, but other than one you own?

Yeah, I was half-expecting that, but other than one you own?

FWIW I can see one too (if I stick my head under the desk).
--
Robin
reply to address is (meant to be) valid

On Nov 15, 2:43*pm, (AnthonyL) wrote:
I'm involved in a small project which needs to respond to the output
from a photodiode.

A Maplin L67BQ power adapter provides the 9v needed to power a LED
which then reflects via a moving mirror to activated the photodiode,
which in turn provides 9v.

Are you explaining this correctly? Photo-diodes are not generating
devices and do not produce a voltage output on their own.


This works fine

On what do you base this statement?

cynic wrote:

Photo-diodes are not generating devices
and do not produce a voltage output on their own.

Don't tell Harry ...

On Nov 15, 7:36*pm, Andy Burns wrote:
cynic wrote:
Photo-diodes are not generating devices
and do not produce a voltage output on their own.

Don't tell Harry ...

Hmmm I had in mind photo-resistive response devices. I normally think
of the devices producing a voltage/current output as photovoltaic. -
Point taken!

"Andy Burns" wrote in message
o.uk...
John Rumm wrote:

On 15/11/2011 17:32, Andy Burns wrote:

When was the last time you saw a PC with a joystick port?

glances to his left about a second ago...

Yeah, I was half-expecting that, but other than one you own?

I have a USB joystick interface somewhere, it was used for a flight yoke.

cynic wrote:

On Nov 15, 7:36 pm, Andy Burns wrote:
cynic wrote:
Photo-diodes are not generating devices
and do not produce a voltage output on their own.

Don't tell Harry ...

Hmmm I had in mind photo-resistive response devices. I normally think
of the devices producing a voltage/current output as photovoltaic. -
Point taken!

Did anyone say VDR (voltage dependent resistor)?

--
Tim Watts

On Tue, 15 Nov 2011 11:40:19 -0800 (PST), cynic
wrote:

On Nov 15, 7:36*pm, Andy Burns wrote:
cynic wrote:
Photo-diodes are not generating devices
and do not produce a voltage output on their own.

Don't tell Harry ...

Hmmm I had in mind photo-resistive response devices.


ORP12.

--
Frank Erskine

On Tue, 15 Nov 2011 20:36:18 +0000, Frank Erskine wrote:

On Tue, 15 Nov 2011 11:40:19 -0800 (PST), cynic
wrote:

On Nov 15, 7:36Â*pm, Andy Burns wrote:
cynic wrote:
Photo-diodes are not generating devices and do not produce a voltage
output on their own.

Don't tell Harry ...

Hmmm I had in mind photo-resistive response devices.


ORP12.

Think I still have one somewhere.

--
Use the BIG mirror service in the UK:
http://www.mirrorservice.org

*lightning protection* - a w_tom conductor

On 15/11/2011 14:43, AnthonyL wrote:
I'm involved in a small project which needs to respond to the output
from a photodiode.

A Maplin L67BQ power adapter provides the 9v needed to power a LED
which then reflects via a moving mirror to activated the photodiode,
which in turn provides 9v.

Is this photodiode a bare component like this:

http://uk.farnell.com/vishay/bpv10nf...pin/dp/1328399

or a module more like this?

http://www.plccenter.co.uk/Buy/ALLEN...Y/42EFB1MNBCA2

If it's the bare component then I think you have a lot more work to do,
if it's the module then read on.


This works fine but the signal has to be taken over about 30m and into
a computer adapter which should detect the voltage but doesn't.

How have you tested it? I guess you have measured ~9V with a meter
connected between the power supply 0 volts and the photodiode output
when the mirror is present and ~0V when it isn't?

On checking, the Maplin adapter appears to be isolated from mains
earth and neutral. So I can register the 9v between signal and the
adapter neutral but not between signal and mains neutral.

I assume the computer is checking the voltage with reference to it's
own neutral, which would be power supply neutral or signal ground.

Do you have any documentation for this adapter? If it is designed to be
used for this sort of thing I would expect it to have a signal ground
connection

How do I get round this?

Are you sure this adapter is designed to take a 9V input? What is it
exactly?

Does this "computer adapter" not have a ground, GND or 0 Volt connection
which it uses as a signal reference? If it does then connecting that to
the Maplin power supply output 0 volts should work. If it doesn't have
such a connection then connecting your power supply 0V output to the
computer case *may* work. However I suggest you come back with more
information about this computer adapter and photodiode before you try that.


Thanks

In article ,
says...

On Tue, 15 Nov 2011 11:40:19 -0800 (PST), cynic
wrote:

On Nov 15, 7:36*pm, Andy Burns wrote:
cynic wrote:
Photo-diodes are not generating devices
and do not produce a voltage output on their own.

Don't tell Harry ...

Hmmm I had in mind photo-resistive response devices.


ORP12.

or an ORP60 if space is at a premium ...


Strange that the OP hasn't been back to respond to the (many) queries
raised by his post ...

--

Terry

On Tue, 15 Nov 2011 17:21:18 +0000, John Rumm wrote:

On 15/11/2011 15:12, Jules Richardson wrote:
On Tue, 15 Nov 2011 14:43:16 +0000, AnthonyL wrote:
A Maplin L67BQ power adapter provides the 9v needed to power a LED
which then reflects via a moving mirror to activated the photodiode,
which in turn provides 9v.

This works fine

Just to be clear, you have a power supply, LED, mirror, and *something*
(I suspect not a photodiode - or at least not in isolation) which is
putting out +9V with respect to the power supply's ground when the
light falls on it?

but the signal has to be taken over about 30m and into a computer
adapter which should detect the voltage but doesn't.

What is this computer adapter?

If you're feeding +9V into an old PC parallel port, you'll probably
break something (they're only designed for TTL levels).

If you're using one of the lines on a serial port, that'll probably
work (although some PCs can be a bit picky, so I'm not sure that +9V is
guaranteed to work despite what the spec might say).

9V is well in spec for RS232C which is what a traditional PC serial port
works to

Agreed - and some more modern far-east piece of crud should, in theory,
work too, I'm just saying that in practice I've seen a lot of duff
hardware at the cheaper end of things - I expect there are some
implementations that are a bit cavalier with the spec :-)

however it only reads digital levels, and does not perform
analogue to digital conversion as such. Fine if all you need is an
illuminated, not illuminated indication - not much use for an indication
of the level of illumination.

Ahh, yes it hadn't even crossed my mind that the OP might be wanting a
voltage in proportion to the level of illumination! Yes, joystick port
probably best bet if the machine has one... or ADC grafted onto the
parallel port (assuming the machine has a parallel port, even - God
modern PCs are useless :-)

cheers

Jules

On 15/11/2011 19:15, Andy Burns wrote:
John Rumm wrote:

On 15/11/2011 17:32, Andy Burns wrote:

When was the last time you saw a PC with a joystick port?

glances to his left about a second ago...

Yeah, I was half-expecting that, but other than one you own?

Is there a point to your question?

I am just offering the OP some options. May be of no use, then again it
might not.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

John Rumm wrote:

Andy Burns wrote:

When was the last time you saw a PC with a joystick port?

Is there a point to your question? I am just offering the OP some
options. May be of no use, then again it might not.

It might be, but I was just pointing out that the number of PCs from the
last decade with a joystick port is vanishingly small. Since the O/P is
already using Maplin kits his project, then maybe something like this
gives him more options?

http://www.maplin.co.uk/usb-experime...ce-board-42857

On Nov 15, 8:36*pm, Frank Erskine
wrote:
On Tue, 15 Nov 2011 11:40:19 -0800 (PST), cynic

wrote:
On Nov 15, 7:36*pm, Andy Burns wrote:
cynic wrote:
Photo-diodes are not generating devices
and do not produce a voltage output on their own.

Don't tell Harry ...

Hmmm I had in mind photo-resistive response devices.

ORP12.

That's an LDR (light dependant resistor)


--
Frank Erskine

In article 5ad8624c-5504-4f57-be58-a71d027e3e46@
4g2000yqu.googlegroups.com, says...

On Nov 15, 8:36*pm, Frank Erskine
wrote:

Hmmm I had in mind photo-resistive response devices.

ORP12.

That's an LDR (light dependant resistor)


which is another way of saying it is a responsive photo-resistive
device, isn't it?

--

Terry

On Tue, 15 Nov 2011 11:30:41 -0800 (PST), cynic wrote:

On Nov 15, 2:43*pm, (AnthonyL) wrote:
I'm involved in a small project which needs to respond to the output
from a photodiode.

A Maplin L67BQ power adapter provides the 9v needed to power a LED
which then reflects via a moving mirror to activated the photodiode,
which in turn provides 9v.

Are you explaining this correctly? Photo-diodes are not generating
devices and do not produce a voltage output on their own.

Yes they can. Look up the phrase "photovoltaic effect".


--
Regards, Paul Herber, Sandrila Ltd.
Electronics for Visio http://www.sandrila.co.uk/visio-electronics/
Electrical for Visio http://www.sandrila.co.uk/visio-electrical/
Electronics Packages for Visio http://www.sandrila.co.uk/visio-electronics-packages/

On Nov 16, 7:15*pm, Paul Herber wrote:
On Tue, 15 Nov 2011 11:30:41 -0800 (PST), cynic wrote:
On Nov 15, 2:43*pm, (AnthonyL) wrote:
I'm involved in a small project which needs to respond to the output
from a photodiode.

A Maplin L67BQ power adapter provides the 9v needed to power a LED
which then reflects via a moving mirror to activated the photodiode,
which in turn provides 9v.

Are you explaining this correctly? Photo-diodes are not generating
devices and do not produce a voltage output on their own.

Yes they can. Look up the phrase "photovoltaic effect".

--
Regards, Paul Herber, Sandrila Ltd.
Electronics for Visio * * * * *http://www.sandrila.co.uk/visio-electronics/
Electrical for Visio * * * * *http://www.sandrila.co.uk/visio-electrical/
Electronics Packages for Visiohttp://www.sandrila.co.uk/visio-electronics-packages/

Weve just been through that enlightenment thanks