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12V Signal On/Off Delay

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Vakito:
Hi all, I'm in need of a simple 12v circuit designing which triggers an output going to a MOSFET for an adjustable amount of seconds.
When the input is turned on, the output should be on for a few seconds (example, 5 seconds) and the same should happen when the input signal is turned off.
Hopefully the timing diagram attached will make things clearer.

Many thanks
Peter

Ian.M:
Well the obvious lineup is a Schmidt trigger to guarantee consistent fast input transitions, an XOR edge detector and a retriggerable monostable for the output pulse, with a variable timing resistor, all in 4000 series CMOS logic.  Even if you cheat and use a quad XOR with two of its gates strapped as non-inverting buffers with positive feedback to make them Schmidt triggers for the input and delay path, that's still two ICs.

I think you can do it with a single 4106 hex Schmitt inverter used creatively.  One gate to square up the input, then AC couple it with a short time constant to get a bi-polarity pulse from both edges, eliminate the negative going half, and square it up with another gate, leaving several gates to implement the monostable.  It *MAY* need a transistor to discharge the timing cap faster than a 4000 CMOS output can manage.

ledtester:
Found this at https://www.electro-tech-online.com/threads/need-advice-on-a-rising-and-falling-edge-sensor-circuit.92431/ which may help:



And ideas for monostable multivibrators using CMOS logic gates:

https://www.electronics-tutorials.ws/sequential/seq_3.html


glentek:
Here's part of a circuit that I designed to control an actuator to open/close a vent. You could combine the outputs with diodes to do what you want.

eblc1388:
Your problem can be solved using a 555 timer set up as a monostable with a 5-second duration. It only needs to be triggered on both edge of input trigger signal to get the desired output.

 

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