Acoustic Trigger

I need to make an acoustic trigger for the cannon. (the big one). maybe one with a variable delay, you could go old school with a tunable RC network, or digital uP. I'd put a long cord on the pickup so I could put it near the impact point, and then adjust delay.

I wonder if you could use a piezzo electric? maybe just use a regular crystal, with no load, and then gain up the response with an op amp. drop the piezzo on the ground and out pops a trigger? tape it to a frozen jug, and use it for the trigger when the jug gets shot. so many possibilities....

found here