# 120V trigger to close dry contacts for .5 seconds

#### MotoLeon

Joined Oct 3, 2019
4
I have a Wyze smart plug that delivers 120V for 30 seconds before turning off that I need to convert to a half a second closure of dry contacts. (to open and close a garage door). If anyone could propose a simple circuit that could accomplish this I would appreciate it.

Leonard

#### ElectricSpidey

Joined Dec 2, 2017
783
Diode…capacitor…capacitor…relay

I’m not at my computer where I can make the schematic, but basically you rectify the 120 volts AC half wave, filter it, then place a capacitor in series with the relay on the output to give a short pulse output.

Oh yea, and a resistor across each cap for discharge.

#### MotoLeon

Joined Oct 3, 2019
4
Diode…capacitor…capacitor…relay

I’m not at my computer where I can make the schematic, but basically you rectify the 120 volts AC half wave, filter it, then place a capacitor in series with the relay on the output to give a short pulse output.

Oh yea, and a resistor across each cap for discharge.[/QUOTE

#### MotoLeon

Joined Oct 3, 2019
4
Diode…capacitor…capacitor…relay

I’m not at my computer where I can make the schematic, but basically you rectify the 120 volts AC half wave, filter it, then place a capacitor in series with the relay on the output to give a short pulse output.

Oh yea, and a resistor across each cap for discharge.

Thanks for the quick reply! This is inline with what I was thinking. I would have loved to see your schematic with some value....maybe if you get a chance!

Thanks again,

Leonard

#### crutschow

Joined Mar 14, 2008
23,811
Below is the LTspice simulation of the circuit proposed by ES.
The yellow trace shows the relay closure time.
R1 is the resistor to discharge the caps after the AC stops (it should be 5W rated).
The value for C1 depends upon the coil resistance of the 120V relay you select (the value of C1 times the coil resistance should be 800ms or greater to get a ≥500ms relay pulse).