# Source for good quality photodiods?

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• 05-14-2009, 12:16 PM
domaz
See this blog post about making a light meter from a cheap light meter cell you can get it at Sparkfun. It looks like if you follow the articles in that blog you will be able to make a light meter fairly easily.
• 05-14-2009, 12:54 PM
Steve Smith
Quote:

Originally Posted by olleorama
Okay, can you explain the last part? Or do you have a wiring diagram?

I will try to explain it. I don't have a diagram as I tend to just build things... but I could do one for you if you want one.

Imagine a counter with a display consisting of seven digits with a decimal point after the fifth digit. e.g. 00000.00 (a bit like a sports stopwatch display).

Every time the input to this counter gets a pulse, it increments by 0.01 e.g. increment it 137 times and the display will read 0001.37

There is also an oscilator which gives 100,000 pulses per second. If it is connected to the counter directly, the count will count up in milliseconds. i.e. after 1 second it will read 1000.00, after 2 seconds it will read 2000.00, etc.

Now if I ad a circuit which only allows the counter to run when there is light on the photodiode then it will only count when the shutter is open and light is falling on the diode.

We then have a simple conversion to do to work out shutter speed:

1 second = 1000.00mS
1/2 second = 0500.00ms
1/4 second = 0250.00ms
1/8 second = 0125.00ms

and so on.

You compare your actual shutter speed with the theoretical speed in milliseconds to see how close you are.

The final part is a reset switch which sets the counter back to 000.00 just before you fire the shutter being tested.

Steve.
• 05-14-2009, 01:01 PM
olleorama
Thanks Steve. I got the oscillator and the counter, but I don't get how you trim it down so the counter shows exactly the mS. How do you get the voltage... Wait, I get it! :D Sort of I think! Electronics is a bit like programming, but IRL, voltage and cycles being important variables :D

Most of the oscillators I see when scimming through my kind-of-local electronic parts shop has a lot of legs, most of them have four, some are like ICs. Some have variable frequencies... Which one to choose? Is there some kind of standardisation, like there is with resistors? There is some different kinds of counters available here, mostly 'impulse counters', that would be the correct type, right?

But again, this would in theory have the same accuracy as the version using the soundcard? Since I can sample in 99.6kHz? Or do I loose something on the way? Which is the most accurate? The sensors are essentially the same, right?

On the microcontroller thing in the blog link, i think that is above me.
• 05-14-2009, 01:02 PM
Steve Smith
Quote:

Originally Posted by olleorama
Okay, can you explain the last part? Or do you have a wiring diagram?

Quote:

Originally Posted by olleorama
Huh? How is that gonna help me?

Well, you did ask for an explanation.

Quote:

Originally Posted by olleorama
For me to use this information I need a specific type of microcontroller, which I don't have.

Mine doesn't use a micrcontroller.

Steve.
• 05-14-2009, 01:08 PM
spark
industrial limit switches commonly use a packaged photodiode or phototransistor mounted in a plastic housing. Break the plastic away and you have a device to use. IR LED's are found in old remote controls. Almost any of these will be fast enough for checking camera shutters.

The counter approach is a good one. Old counters can be found at electronics flea markets for about \$20-\$30. A 20 MHz one is very slow by today's standards but fine for 1/1000 sec (1/0.001 MHz!) shutter speeds. For an oscillator- get a 10 or 20 MHz one and add a few cheap CMOS chips to divide by 100 or 200 to get 100 kHz.
• 05-14-2009, 01:14 PM
Steve Smith
Think of it like a very fast version of a stopwatch as used for sports timing. When the shutter opens the watch starts timing, when it's closed it stops.

The only difference is most stopwatches work in hundredths of seconds whereas a shutter tester works in hundredths of milliseconds.

Steve.
• 05-14-2009, 01:16 PM
olleorama
Quote:

Originally Posted by Steve Smith
Well, you did ask for an explanation.
.

Sorry for that, that was aimed at the post above you, if you follow his link you will see.. :(

Your post just happened to come between, I just didn't quote him. Ok? Sorry again.
• 05-14-2009, 01:22 PM
Steve Smith
I used one of these for the oscilator: http://www.fairchildsemi.com/ds/CD%2FCD4060BC.pdf (4060)

And six of these for the counter: http://www.edutek.ltd.uk/Binaries/Da...00/HCF4026.pdf (4033)

I can't count. It's a six digit display, not seven!

Steve.
• 05-14-2009, 01:59 PM
olleorama
Okay, I'm *very* impressed by the skill and knowledge people have here. But knowing is one thing, understanding is a second, and actually building is a huge third thing. I have ver little experience in building these kind of things. So it will take a long time for me to put this together.

Quote:

Originally Posted by Steve Smith
I will try to explain it. I don't have a diagram as I tend to just build things... but I could do one for you if you want one.

Yes, that would be incredibly nice. Then I just need to find the parts. Suddenly everything took a big giant leap from scrapheap sensor to hitech counterbased sensor. But as long as I good something pretty accurate within a reasonable budget and complexity I'm happy.
• 05-14-2009, 02:18 PM
BetterSense
People are making this way too complicated. If you just want to use your soundcard or a scope or some other input, then all you need is a photodiode/phototransistor and a resistor. And a AA battery. I made one like that and used it a lot until I made my microcontroller-based one. It works fine. Note that the simplified diagram shown will dump a square wave into your soundcard, but for the short speeds typical of shutters, it shouldn't be a problem. Mine uses a capacitor and a pot, so it actually outputs two spikes, one when the shutter opens and one when it shuts. Using audacity you can just highlight the distance between the shutter opening and shutting, and it reads out the time value of the highlighted selection in seconds at the bottom of the screen.

http://i109.photobucket.com/albums/n...on/shutter.jpg
http://i109.photobucket.com/albums/n...7090934a-2.jpg
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