Hey everyone. Got a weird request that I need to design hopefully with minimal components. Hoping to avoid using a microcontroller...

I have a circuit where I can flip a switch and that switch turns ON 5 volts output
With this 5 volt output I need to activate another circuit momentarily for just 1 ~ 2 second and shut it off.

Does anyone have any idea how I can go from switch ON permeant to temporary/momentary 1 ~ 2 second ON and off while the original trigger is still ON and suppling 5volts?

It doesn't really matter if the circuit is crude or terribly designed... simpler with least amount of components is the preferred goal here

Any advice much appreciated
ツ

 

The circuit is called a monostable multivibrator.

 

What is this other circuit?

 

I'll look into monostable multivibrator, thanks.
And the other momentary circuit has to be insulated to I'll portably just use a mini relay

 

Ahhh I found something, looks like someone was looking for the very same thing.

I think this should work?

 

With that circuit the relay will activate briefly when the switch is turned on and off unless a diode is installed across the relay coil.
How long the relay stays activated will depend on the resistance of the relay coil and the capacitor value.

 

I just quickly tested it on the bench and it seems to do exactly what I wanted... keep the relay open for a few seconds.

I only had to add a discharge 5k resistor in parallel with the cap to help discharge the cap after use and get it ready faster for next cycle.
Also used a bigger cap 2200uF to keep the relay open a bit longer.

Im actually surprised how simple the solution was, just a cap in series and a resistor across it.
I wanted it simple, didn't think it would be this simple

 

This could work. D1 serves just as dummy reference to put Npn comparator voltage bit higher, like 1.4V, where RC exponential curve has “faster” slope.

Because of two diode OR gate the Npn comparator switches off when minus side of 470u capacitor is at 2V1 (1.4V comparator +0.7V OR diode drop).



Compared to your relay circuit this one has much faster turn off edge, and doesn’t need a huge timing capacitor. Also doesn’t suffer for SW contact bouncing.

Or bit easier if you got a mosfet:

 

I only had to add a discharge 5k resistor in parallel with the cap to help discharge the cap after use and get it ready faster for next cycle.

Adding D1 and R1 will allow a faster discharge of C1.

 

The circuit in post #5 will work!! The diode and resistor in post #9 contribute nothing!! AND no protection diode is required because the relay current does not drop rapidly. The diode should tie to the positive end of the capacitor instead.

 

The circuit in post #5 will work!! The diode and resistor in post #9 contribute nothing!! AND no protection diode is required because the relay current does not drop rapidly. The diode should tie to the positive end of the capacitor instead.

Not about protection.
The diode and resistor allow the cap to discharge rapidly bypassing the relay coil otherwise the relay coil will activate briefly when the switch is turned OFF.

 

GOOD POINT!!