I've been asked by a friend for help on some projects. One involves building a simple beeper circuit, but I'm having trouble filtering a bunch of Google crud, and I really don't know specifically where to look for simple general circuits. What I'm in need of is something that is cheap and simple to build and can produce sound at a variable rate, say from once every couple second to once every 20-30 seconds. I've thought it should be easy to make something from a 555 timer, but I have little hardware design skills. I know that something could be built using a few resisters and a capacitor. Beep timing would probably be waiting for the cap to charge, then emitting a sound from a piezo or something as it discharges. Anyone know of a circuit I could use, or have more design tips? Cheap simple and rugged are the top criteria.
The two uses it would have would be to help training of search and rescue teams for "stop and listen" skills, so that they wouldn't rely on their search dogs as much, and also use on high altitude balloons for recovery.
I'm perfectly willing to share credit for ideas, as I only told him I had a few places to check online for circuit and ideas. AF being one of them, of course.