Need help with a door solenoid

[gosparky]

The 12v solenoid only needs a short pulse from a bell button.

The problem is if the bell button is held depressed and the 12v are continious to the

solenoid. Can someone help me to a simple circuit to only give a pulse, no matter how

long the bell button is held depressed ?

Thank you
Bert Plante

[KMoffett]

What you are looking for is a monostable multivibrator type circuit. Check out 555 monostables.
Or, the simple circuit attached. Just replace the relay with your solenoid. You didn't say how much current the solenoid draws. If over 500mA, you would need a higher power MOSFET than the 2N7000.

Ken

[gosparky]

Thank you Ken,
Since i am in the shinola group could you help me with the type of capacitor so i can

build this circuit?

I was also wondering if there was a premade type of circuit that would be in series

with the switch, power source and solenoid to open up after a small amount of time,

so that continuous depression of the switch would cause no harm.

Thanks for your help,
Bert

[KMoffett]

The capacitor is an electrolytic type. Any 4.7uF with a voltage rating of 16V or greater. Off hand, I don't know of a 2-wire inline monostable switch.

Ken

[JMACgyver]

Perhaps just a self-resetting breaker or thermal fuse rating at just above what the circuit normally draws?
That way, under normal momentary operation the solenoid will trigger like it should. When the button is held for a longer period of time, the solenoid is just building up heat in the coil, and drawing more power, causing the fuse to trip. Then, when the temperature dissipates, or the current draw lowers, the fuse resets and the circuit works normally again.

Maybe you can replace the spring in the switch itself to make it harder or more uncomfortable for people to hold it down for longer than necessary.

Regards,
--Electro--
aka The Other David