arming a relay for a period of time


i have realised this electronic scheme. It is working very well. it allows to activate a solenoid.
is it possible to add a capacitor on this in order to arm the relay for a period of time ? (10min, 20 min, 30min or 60min)

have you got example scheme ?

Thanks in advance

May I ask why you want to try and hold the relay with a capacitor when you already have a microcontroller connected?

yes i know ! so i should use millisec function ?
for my part i prefer to do by the electronic way ...

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Well, you could add a 555 timer. A capacitor by itself really isn't a good idea, as then the relay will tend to drop out slowly.

It seems much simpler to add it in software. Yes, I'd use the millis() function.

You definitely do not want to use analog electronics here, its a switching circuit.
Switching circuits are only efficient in two states, on and off - anywhere inbetween
and the power dissipation in the switching device will be a lot higher - for no
benefit at all.

You do the delay in software, which is effectively free and you have a simpler
circuit with less components to fail.

If you were to do this in hardware the method of choice is using a monostable
such as the 74HC4538.