Hi All,
As an introduction I'll say that I've had a long time intrest in electronics, made a few projects over the years, and had a ham license for awhile. But a few years ago I made a remote controlled electro-pneumatic unit that pulls a cable that turns a set of targets for the indoor range where I shoot using circuits and parts that I got off the internet, and it actually works! It has settings for keeping the targets faced 2, 5, 10, 20, and 60 seconds. I used 555 timers and 434 mhz tx and rx from Reynolds Electronics. We now have need for turning targets outside but until we can afford to build a pneumatic setup for outside I want to use the controller that I made for the inside unit to run an air horn as a signal to begin and end firing. If the controller is set for 20 seconds the horn needs to blow for lets say one second at the beginning of the of the time and then blow again at the end of the 20 seconds to signal the end of the firing period. I'll get another 434 mzh rx unit and I can control the length of time that the horn blows with more 555 timers and some power relays so the question is how to to make the horn blow at the end of the 20 seconds when the signal goes from high to low.
TIA,
kilojoe