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simple Time delay relay circuit

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Fletcher

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I need help, want i want is a very small circuit to detect 5v and then to turn on a 5v relay about 5-7 seconds later.

Does anyone have any links or ideas?
 
I've not calculate the condenser, the value about 10uF. For exact timing You can experiment also with the charge resistor (68k).
 

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time delay computation

:D hi,

here's the formula you can use to compute the time you would want:
T = 1.0986(RxC) time is in seconds

using the 10uf cap
w/R = 68K - 7.4s, 62K - 6.8s, 56K - 6.1s, 51K - 5.6s, 47K - 5.1s


to sebi, i also had made a circuit somewhat similar to that, i used an SCR to drive the relay. :)
 
I see the point with the time delay circuit but Fletcher also wanted the circuit to first detect 5 volts and then delay the turn on time of the relay. I think a comparator voltage level detector would come in handy here. It appears the delay circuit would also require some means of initializing the delay when the 5 volt level is detected.
 
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