Hi -- I got one of these SSR's, which trigger on 3-32 VDC. It's driving a load at 12 VDC. Unfortunately it needs 5mA to trigger, and the 2mA (if I have that right) of the Arduino Zero GPIO pin is not sufficient, so I wired up a PN2222A to drive it. But I'm doing something dumb, because it's not wo…

I don't see the Arduino GND in your diagram. Also adjust the base resistor to limit the current to 2mA.

Yeah it's just a typical 5V wall wart supply plugged into the USB input. I was wondering if the arduino GND should be tied to the 12V PSU - ?

[image] savel: arduino GND should be tied so that current can flow into the base and back to the Arduino.

Normally I dont think a SSR would require a transistor...

[image] savel: arduino GND should be tied so that current can flow into the base and back to the Arduino. Gotcha, will do. It always feels "weird" to me for some reason to tie separate PSUs together, but clearly my intuitions need a lot of adjustment. :slight_smile: [image] westfw: Norma…

Would that be smarter? Instead of what you drew, I'm powering the SSR input with the 12V supply (see my post #6). It was much more convenient to wire it that way in the physical installation this is in, but if that's dumb for some reason I could use the 5V from the arduino as you showed...

My drawing isolates the ZERO from the 12V circuit (separate grounds}, also, I should have drawn in a 1k transistor base resistor, 220Ω is a little low IMHO. But if your way works OK, proceed.

[image] savel: AFAIK the arduino GPIO only supplies 2mA, right? No. The spec page states "7mA" Zero | Arduino Documentation | Arduino Documentation

From datasheet page 875, 7mA? [samd21] 3.3V - 0.7v = 2.6V / 220Ω = 11.8mA !! Blown GPIO pin?

An SSR input is an IRED and a series resistor. I would suppose the current given a 3V signal is <= 2mA. (I would assume 20mA with 32V applied. I could be wrong.)

Triggering an SSR from Arduino Zero with NPN -- what's my mistake in this schematic?

Other Hardware General Electronics

JCA34F April 6, 2023, 12:45am 13

Like this?
schemeit-Project

Why PWM not working with SSR-controlled fan?

Topic		Replies	Views
Driving SSR wiring diagram General Electronics	18	5792	January 18, 2022
Wiring a solid state relay to Arduino General Electronics	16	7929	June 19, 2024
Driving a high current SSR Relay with an ESP32 GPIO Pins General Guidance	27	4089	April 29, 2025
Simple circuit with NPN issue General Guidance	171	1212	December 3, 2025
Why PWM not working with SSR-controlled fan? General Electronics	19	1435	October 5, 2023

Triggering an SSR from Arduino Zero with NPN -- what's my mistake in this schematic?

Related topics