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Topic: Timer Circuit needed

Frank Angel
Film God

Posts: 5305
From: Brooklyn NY USA
Registered: Dec 1999

posted 09-07-2011 04:24 AM

The landlord has installed a new video intercom in our apartment. Spiffy. Really nice one with a color screen. It can either sound one of those annoying digital telephone sounding rings which both of us hate OR, its chirp can be turned OFF and it gives you the choice of a contact closure so you can use whatever bell device you want.

Here's the problem. Our door bell is a common type with two REAL tubular chimes that ring the standard DING, DONG when voltage is applied and released. We like these REAL chimes --the artificial ones with a little 3 inch speakers suck.

These two tubular chimes are struck with a spring loaded hammer that is pulled in by a solenoid when voltage is applied and it hits chime #1. When the voltage stops -- in normal situation, that's when the visitor releases the doorbell button -- the hammer slaps back and hits chime #2; this happens in fairly rapid succession, as in DING .5 to 1 second, or for however long the guy holds down the button.

Problem now is, the new intercom closes the relay supplying the 12vdc to the solenoid not for 1 second, but for about 20-25 seconds. So now we get a DING.....(20 seconds).....DONG. She doesn't like her dongs that long.

The way I play movie soundtracks -- at correct Dolby reference, of course -- I need more bell strikes in more rapid succession if we are going to hear if someone is at the door. So what I am looking for, is a circuit that will time out in say 1 second after the voltage is applied; voltage OFF will release the solenoid and let the hammer hit the second chime. Then the presence of the 12volts which is still there will charge the circuit and 5 seconds later will send 12v for a 1 second ON/OFF cycle again, 5 secs to recycle and so on until the intercom stops sending 12 volts. So when 12v is applied for 20 seconds, the end result will be: 12v ON 1sec OFF 5 secs -- 12v ON 1sec OFF 5 sec, etc., for as long as the 12v is present.

That will give us a succession of timed DING, DONGs so we won't miss visitors. I have no idea how you compute the different timers. Easy to get an even ON/OFF cyle, but how to get one at 1 second with the other at a 5 second wait? Without this modification, we will never hear when someone is the door when we are watching a movie. Then again, maybe that is a good thing considering how anti-social and nasty I get when 1) we are interrupted during a movie by someone AT THE DOOR, and 2) when people DO come in, there is that 70/30 chance that during the movie they will want to TALK to me. Of course the MAIN reason that I CAN'T miss the door is that I won't be able to get the PIZZA DELIVERY. So you see, I HAVE to solve this problem.