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Looking for help making a simple on/delay/off circuit.I? Answered

I am looking for help making a ( hopefully simple ) circuit to drive an electronic relief valve.
What I have is a push button on a linkage and an electronically actuated valve.
I'd like a circuit that, when the button is pressed, will supply a 12v output for roughly 500ms immediately after the button is pressed, which will then turn off. The circuit must then remain off while the button remains held, until it is released and hit again. 

Linkage open / Valve closed> Linkage closed / Button pressed >Valve open 500ms> Valve closed / linkage remains closed > Repeat

The system is for a turbocharged diesel engine. When the throttle is snapped shut, the boost pressure has nowhere to go. It tries to run back out the compressor housing. This results in a forceful drop in turbine RPM, and in extreme cases even completely stalling the turbine ( and blowing it to pieces ) I intend to vent this pressure back pre-turbo via a 2 inch valve. The short delay upon closing the throttle with this size of valve should be more than adequate. I also intend on wiring a boost pressure switch to disengage this circuit below 15psi. The turbo's anti-surge housing is effective at the lower pressure.

Any help with the circuit would be GREATLY appreciated! 


A waste-gate ? The ones on my diesels are pressure activated, not electrical.

The simplest method is called a one-shot, and can be made with a 555 timer. This circuit http://clarkson-uk.com/555-timer/operation/frames4.html does precisely what you need. Plug your numbers into the little calculator.

AFTER this stage, you need a transistor or relay to drive the solenoid


Not quite. The wastegate regulates pressure on the exhaust side of the turbo. It is boost driven, and after X amount of boost it lets the exhaust bypass the turbine. ( gradually ) I'm looking to bleed the intake side of the turbo when I let off the throttle.

That page looks exactly like what I need. Thanks! :)