Regarding my previous post; what is the practical limitation to continuous photo shooting with a Canon S3IS via the usb cable?
If I'm not mistaking, when you have the camera in continuous mode and hold your finger in the control button, it will keep shooting. I mean, while there is a voltage present at the USB cable, the remote control script will shoot indefinitely. I will try it tonight to make sure.
So, I guess what you could build is some kind of circuit with a microphone and an amplifier. The microphone will give you mV when it hears a sound and you have to amplify that voltage up to 3V. That's to take a shot if you clap or something.
To take multiple shots you can go either the hardware or the software way:
In a hw solution you need to hold those 3V for a few seconds may be using a timer like the 555 you mentioned. You can adjust it to give you a pulse, say every 5 seconds and when there is a voltage present at the microphone the 555 starts counting and provides the 3V needed.
In a sw solution, you just modify the control remote script to hold the shooter button for several seconds.
IMO the software way is easier. I can help you with the script if you want but I bet you can understand it anyways, it is pretty easy.
P.S. You can add a potentiometer to the cirtuit, so the user can addjust the level of sound needed to trigger the camera.
