Countdown Timer Circuit...

[Racer53]

I am trying to build a countdown timer that acts as a relay and completes another circuit when the time is run down...

It needs to be as cheap as possible and I would like to do it without micro-controllers...It needs to be able to countdown from 60 minuters 59 seconds...So if I use LED number displays I need 4 total...I am also open to using LED's alone without the number displays...I am looking for a simple design, nothing to complicated or expensive...

Any help is appreciated...

 

[Reloadron]

You would want MM:SS to start as 59:59 and count down to 00:00 on the display. One way to do this would be with a one second clock driving 4 each cascaded 74192 programmable BCD output up / down counters. The DCBA out of each counter would drive a chip like a 7447 BCD to 7 segment decoder driver that would drive 7 segment common anode displays. A good start would be to read the data sheet on the 74192 which can be found here. That is just one way to go about it. There are other chips out there that will do it.

Ron