Looking for a Low Cost On Delay Timer

Guv Bob · 2013-08-21T17:39:11+00:00

Names can be confusing, so here's what I'm doing.... When 12VDC is applied to the input, I need a 12VDC output for 5 seconds. Then output will go back off and stay off until the input goes to zero. Then cycle starts again. Current for both legs is in the 10-50ma range. A simple on-delay timer would work but I'm having trouble finding one with NC contacts. Tons of stuff $100+, but for this application, it has to be under $20. Thanks, Bob

Aug 21, 2013 25 Replies

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Guv Bob 13 years ago

seconds. Then output will go back off and stay off until the input goes to zero. Then cycle starts again.

one with NC contacts. Tons of stuff $100+, but for this application, it has to be under $20.

something together from components but my brain is too far behind these days. I'm going to give this a shot and hopefully I'm not picking the wrong one. It's $5 at Frys...

Well, I made a real mess of the first board, thanks to a new Weller soldering iron. Ended up digging out my old Radio Shack iron which worked 10 times better - same type and wattage as the Weller. Here's the soldering job on each board....

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Anyway, I made the changes Spehro mentioned and it works perfectly!

First I snipped the R3 out of the circut which caused the LED to act as a one-shot as needed. So with that good news, I added the jumper and now the relay is in the circuit and I am in Fat City!

FYI, on the left is the assembled board from the kit. Right shows it with the jumper added.

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Thanks again to all for this very educational journey!

Bob

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John Sowden 12 years ago

Get a sensitive relay (coil 1k ohms or so), put about a 3ooo uf capacitor across the coil, apply 12 volts to the coil, the relay will hold closed while the cap is discharging into the coil. Use the n/o contacts to do what you want.

John Sowden American Sentry Systems, Inc. San Francisco Bay Area

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