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     Aphototaker Tinkerer Username: Aphototaker Post Number: 277 Registered: 12-2009 Rating: N/A |
You probably mislabeled the switch. Where is your switch in the circuit precisely? Yes, determining the proper input for your card is sometimes tricky. But once you know which input works, it is quite consistent. Remote controls usually emit pulses, as you discovered. A constant source could be better. Some video cameras have this night vision mode which is basically infra red light. If you have one, try that instead. But usual LED or incandescent lamp flashlights should work as well. It also helps to try the maximum sampling frequency of your audio card. I usually do this at 96 KHz. Determining speeds faster than 1/1000 s is mostly tricky. Remember that the signal coming into your card is dc filtered. So if the voltage across your audio input changes, you will only see a spike (the new voltage won't stay at the new level) and the wave form will eventually do down almost zero. This means that at slower speeds, you will see two spikes in opposite direction. At 1/1000 s and faster speeds, the slope of the spikes curves is too shallow to make a reliable demarcation of the shutter opening and closing. This can potentially be improved by restricting the photo detector's receptive area with mask with a sharp hole, but I haven't tried this yet. Feel free to ask questions. That's what this forum is about! Good job! |