Detect 1Hz square wave to operate relay

eetech00

Joined Jun 8, 2013
3,418
Constructive comments...

Automotive flash rate is usually 0.3-0.5 Hz (1,1.5s on, 1,1.5 off in U.S.) .
The circuit will need to discharge quicker.
There will also be a large inrush current when the big cap begins to charge.
 

eetech00

Joined Jun 8, 2013
3,418
Surely the relay will operate with continuous 12v but also when "square waving", which is not what is wanted
A passive type circuit will require large capacitances with difficult to control timing edges. Smaller caps are better but the timing will need to be amplified by a transistor or chip. Perhaps you can relax your restriction on the use of transistors/chips?
 

Thread Starter

nags14

Joined Apr 26, 2018
13
As the average voltage when square waving is only 6v, if the ciruit could average the voltage, 6v would be not enough to operate the relay, but 12v would.
 

Thread Starter

nags14

Joined Apr 26, 2018
13
If it can be on when the input is steady, then just use D2 and C2 from Albert's circuit in post #16.
No, if on for square waving, it needs to be off when 12v is continuous.
It can be on when 12v continuous, but then it must be off if square waving
 
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