Bit of electrical help please

[Frank Erskine]

ORP12.

[Bob Eager]

Think I still have one somewhere.

[Gareth]

Is this photodiode a bare component like this:

a module more like this?

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

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?

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

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.

[Terry Casey]

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 ...

[Jules Richardson]

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 :-)

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

[John Rumm]

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.

[Andy Burns]

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?

[AnthonyL]

I think this may be the problem. A slightly different installation elsewhere has used a computer power supply (removed from the computer). I haven't had the opportunity yet to check if a separate ground signal wire is taken from the led/diode circuit or whether they were able to get away with the mains earth/neutral to complete the loop.

I suspect that we need to feed the neutral from the circuit board (ie power supply) down to the computer.

I should explain that I have come into this project late as a "troubleshooter". I don't have the computer end at the moment but basically it is a made up box which feeds into a COM port via RS232.

The change state of voltage from +10 to 0 or vice versa is picked up by the software which directly addresses the COM port but that is another story.

For other respondents I apologise if I've been a bit brief with some of the detail. The led and photodiode are on a circuit board with necessary components. The light from the led is reflected back by a mirror on an oscillating wheel with a period of approx 2secs. It is necessary to analyse when the mirror passes to within a few msec. The circuit design provides a 9v signal output (relative to the power supply neutral) when the light is reflected.

The design with minor differences works on other installations and the guy doing this particular one has run into problems. We are all amateurs at this and I am the most technical person in our group to help having done Mech Eng and IT. Not ideal I know and I'm rusty on it all anyway, otherwise I wouldn't be posting here.

Yes this is in the back of my mind too. But in a simple test situation with a reel of approx 50m of unshielded Cat 5 a very clean square wave is seen on a scope. However that is not on-site so other factors might come into play.

Cheers

[John Rumm]

are also loads of data acquisition / controller cards out there that do similar things.

Having said that, with a bit of lateral thought one can often get information into a PC using existing standard interfaces in novel ways.

[Jules Richardson]

I can see three from where I'm sitting (although admittedly I did cheat and looked at the same one an additional two times)

:-)

[whisky-dave]

That's an LDR (light dependant resistor)

[Terry Casey]

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

[Paul Herber]

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

[cynic]

Weve just been through that enlightenment thanks