Kevin's sound-triggered flash circuit

This circuit works by amplifying the positive-going pulse that comes from the condenser microphone when a loud noise (such as a balloon popping or a gun shooting) occurs. The amplified pulse is use to trigger a sensitive-gate thyristor, which in turn triggers the flash circuit. Here are a few notes about the circuit...

I used a triac instead of an SCR because the triac was the only sensitive-gate thyristor I had laying around. A sensitive-gate SCR would work just as well (and make more sense in this circuit). Be sure to use a device that's rated for at least 400 volts, since camera flashes often produce 330 volts.
Adjust R1 until the steady-state voltage at B is around 4.5 volts (half of the 9 volt supply).
When a loud, fast pulse of sound comes into the microphone, in the time that A has risen 100 mV, B has fallen 4 volts, in about 10 microseconds.
Put the condenser microphone on a piece of thin coax or shielded cable, so the cable does not pick up all kinds of electrical noise from house wiring, etc.
The delay between the loud noise and the triggering of the flash can be adjusted by moving the microphone closer and further from the source of the noise. Balloon pops are fast enough that moving the microphone back and forth by a foot or two is all that's needed.
A 9-volt "transistor" radio battery works great to power this circuit.