Easy to build open source shutter tester

[Nicholas Lindan]

High speed is possible with a photodiode. However, you need to do the following:

• Reverse bias the diode - 12V if you can, 5V if that is the only thing available
• Use a high speed CMOS or FET op-amp in I->V configuration. Use as little gain as possible, the opamp should be in it's linear region when exposed to the open shutter. You may need to add a ~10pF capacitor in parallel with the feedback resistor to prevent 'gain peaking,' the capacitor compensates for the opamp's input capacitance, the photodiode's capacitance and any stray capacitance in the wiring. A TL07x should work - it is a 'popcorn' part: readily available and cheap.
• An LM339/LM393 comparator is sufficient, available in most folk's junque drawer.

 

[bjpirt]

Thanks Nicholas - will play around and see how I get on. It's stretching my electronics capabilities so any advice is much appreciated.