Hollywood-Style Beeping Timer
somebody set us up the bomb

I made this in the span of a week when we were doing 555 timers in an electronics class I'm taking. It was a good use of 555 timers, Op-Amps, and logic gates.

The timer starts off by one 555 pulsing another 555 at a constant frequency (one 555 controls the tone of the beep, the other how often it beeps per second). After a certain amount of time has passed, the timing capacitor charges to the voltage set point of an Op-Amp running as a comparator, and a 2nd capacitor begins to charge controlling the pulsing 555. This increases the frequency, until the cap controlling the pulse rate reaches a certain voltage, at which point another comparator flips, setting an OR gate high, resulting in a solid tone.

I'm busy writing up schematics in EAGLE. I've never used this program, and its going a bit slowly since I'm trying to pick optimal chips as I go along. It should be done soon though, at which point I'll etch out a circuit board for it.