Simple(?) Electronic device question

Factual Questions
1

IAMAEE, but I would think it would be fairly easy to create a simple electronic device which would, at the touch of a button, sound a horn then delay for a specified period of time (e.g. 5 seconds) then sound the horn a second time. It would then either automatically reset, or be manually reset for then next run.

This device will be used as a starting signal for a race. Contestants can take a running start, but if they cross the start line before the second horn blows, they are disqualified for that heat. We currently use a person with a stopwatch and a whistle. The person calls “Time”, counts 5 seconds with the stopwatch, then blows the whistle. Human reflexes being what they are, the actual time before the whistle blows tends to vary somewhat. I believe an electronic device will be more consistent and accurate.

The device I invision would be a small box, preferably battery powered, with a horn or speaker mounted somewhere, perhaps a volume control, a start button or switch, and maybe an LED readout where you can set the desired delay. I believe I can get most of the necessary components from the local Radio Shack, but if someone out there can tell me exactly what components are needed and maybe provide a diagram of how to properly connect them, I would be most appreciative.

2

If such a thing already exists, the people on these Newsgroups should be able to tell you:

http://groups.google.com/groups?group=sci.electronics.design

http://groups.google.com/groups?group=sci.electronics.basics

I’d say that this is an intermediate-level proejct, so if you’re new to electronics as a hobby, this might be quite a big job for you.

3

The easiest way to do this would be to use a small microcontroller like a PIC. The microcontroller only costs about 5 bucks and can handle everything from the timing delay to the user interface (LED/LCD readout and switches). PIC outputs aren’t anywhere near beefy enough to drive a horn, but a transistor driver and maybe a relay would do the job easily enough.

Anything with relatively long timing intervals or weird timing (like a programmable time delay) is more easily handled by a microcontroller than a discrete timer like a 555.

The louder the horn the bigger the battery you will need.

Radio Shack doesn’t sell PICs.

Drop me an e-mail if you need some help with the design.