enter image description here

Hello, i build a system which suppose to run speed control of electric engine, with loginc of Raspberry Pi.

Control Signal does not go through SSR.

System Connection Logic:

(1) RaspberryPi 3 ->

(2) Bi-Directional Logic Level Converter Hookup Guide ->

https://learn.sparkfun.com/tutorials/bi-directional-logic-level-converter-hookup-guide to change 3V3 logic to 5V logic

(3) SSR-40 DA ->

https://www.amazon.com/SSR-40DA-Solid-Output-24-380V-SSR-40/dp/B07FVHWN82 to change input signals from DC to 230 V with optocoupler, zerophase and triac

(4) PSC Engine, 1phase, 0,35 A, 1,5 mF

enter image description here Electronic circuit schematics of SSR, https://www.youtube.com/watch?v=WLP_L7Mgz6M - Solid State Relay || DIY or Buy,

Problem description:

Engine speed control is being build. At the beginning i though that SSR itself, will be sufficient solution, to command signal ON/OFF, between computer and motor.

It didn't worked. DC signal from 3V3 GPIO, can not open signal on AC side, and Raspberry do not have 5V control system.


  1. While using SSR: I can run engine, if i connect DC side of SSR to constant 5V pin. (if i connect DC side of SSR to constant 3V3 pin it DOES NOT work).

  2. While using SSR: Yes I can control speed control when using mechanical relay like JQC3F-5VDC-C between Raspberry and SSR, where 3V3 signal opens logic, and 5V is let through to SSR.

(But i do not want to use this solution - mechanical relay wont last long with such a frequent work)

  1. To have other device in the middle, instead of Relay, I bought (2) Bi-Directional Logic to let 5V goes, but it does not move the engine.

  2. I connect (2) Bi-Directional device to control Mechanical relay, (to check if (2) works), it is proven that (2) works

What i need to know:

So far as,

  • SSR with 3V3 signal directly Raspberry Logic AND

  • SSR with 5V signal indirectly through (2) Bi-Directional

do not let me the 230 V through,


  • 5V Signal indirectly through Relay does let me to control the speed

what i suppose to change in the system to make it work,
Is there any resistor i suppose to put in series somewhere in the system, or what?

Thank you!

  • \$\begingroup\$ They have a datasheet at the Fotek site: LINK Looks like they list the trigger current as 7.5 mA @ 12V. \$\endgroup\$ Mar 31, 2020 at 17:12

1 Answer 1


You are not supplying enough current to the SSR to turn it on.

According to the datasheet the trigger uses 7.5 mA @ 12 V.

5V is probably enough, but your level shifter does not allow enough current.

You can probably get this to work with just a logic-level MOSFET and 5 V:


simulate this circuit – Schematic created using CircuitLab

  • 1
    \$\begingroup\$ That works, actually I did it shortly after the original question was published. I used 2N2222 Transistor with 220 Ohm resistor at the gate, and logic works, thanks! \$\endgroup\$
    – hkjz
    Apr 1, 2020 at 9:37

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