I am trying to use a 5v relay (SunFounder Relay Module for Arduino and Raspberry Pi 5V DC Trigger by HIGHLO (HIGH Trigger) to be exact) and I am running into some issues. I have a python script

import RPi.GPIO as GPIO
import time

channel = 21

# GPIO setup
GPIO.setup(channel, GPIO.OUT)

def motor_on(pin):
    GPIO.output(pin, GPIO.HIGH)  # Turn motor on

def motor_off(pin):
    GPIO.output(pin, GPIO.LOW)  # Turn motor off

if __name__ == '__main__':
    except KeyboardInterrupt:

to control the relay from my Raspberry Pi Zero W. As the script runs, I see the blue LED on the relay turn on but I do not hear an audible click. The device I am attempting to test this with (turning on a micro usb device using the relay) does not turn on either.

  • Some relays (I am unsure about the one you have) require a reasonably high load connected to the load side before it will activate. Can you try powering something with a higher load? Perhaps the spec sheet for the relay could provide guidance. – stevieb Apr 1 '18 at 15:25
  • How are you powering the relay? Do you have a separate power supply for the coil? If not you may not have enough voltage and/or current available to pull it in. – dlu Apr 3 '18 at 23:00
  • You need to explain how you are triggering a 5V relay from the Pi, otherwise this is just the same as the piles of identical questions we have here where someone is trying to use a 5V device with the Pi's 3.3V logic. It will not work that way. – goldilocks May 6 '18 at 10:09

It is very likely that your module circuit is similar to that below.

relay module

Module spec says 5V High to trigger.

That means S input expects 5V to trigger. If your Rpi GPIO outputs only 3V3 actually a bit less), then the current through Q1 is not big enough to turn on the relay. The Led still turns on BUT NOT FULLY ON!

To prove that my guess is correct, you can do the following.

  1. Disconnect Rpi GPIO from input S.

  2. Use a jumper wire to connect input S to 5V, relay should turn on, with an audible click.

Then connect input S to 3V3, then blue led should grow brighter, the relay might turn on (because 3V3 is a bit higher than you GPIO signal). If relay is still not on with 3V3, then you need an external device to shift your GPIO signal higher, to above 4V perhaps.

There are many ways to level shift up your GPIO's 3V3 level signal to 5V0 level. You can google SE for more info.

I show below one similar relay module. I did the test without connecting to the rpi (especially not connected to the 5V pin on the RPi 40 pin socket. My module uses a different coil and NPN transistor instead of PNP. But I think the electrical characteristics should be very similar.

enter image description here

There are many ways to do level shifting. I first learnt the idea from NXP


NXP I2c Logic Level Shifting Notes

Then I assembled a I2C level shifter using 2N7000.

2N7000 logic level shifter

Then I tried the MCP23017 io expander, and mux 4 of them, so that I can control 64 relays together.

You can get the idea of the i2c mcp23017 way from below.


The above are a bit challenging and might take you weeks to catch up. If you are in a hurry, I would suggest you AdaFruit or SparkFun's tutorials for beginners. They also sell newbie friendly modules to help you jump start.

Actually logic level shifting might not be the easist solution for you. You may consider throw away your BJT transistor input module and get photocoupler based module. Then you can keep you gpio pin signal at 3V3 logic level, and the 5V0 power at JD Vcc is strong enough to energize the coil.

There are many advantages of using photocoupler. You might like to google to know more.

rpi 3v3 gpio to 5v0 relay module connection

Logical level shifting using HCT125

If you find ic2 stuff too hard, you may like to try the easier HCT125. Adafruit has a good tutorial, and rpi example. I have been using HCT125 in some of my project, using 4 chips to up shift 16 rpi gpio pin signals. You can use OE to disable and mux to as many pins as you like. But the wiring is a bit messy.

74AHCT125 - Quad Level-Shifter (3V to 5V)


... Level shifting chips let you connect 3V and 5V devices together safely. ... particularly good at converting 3V logic up to 5V. ... We have a wiring example for Raspberry Pi here

HCT125 x 2 board assembly

Logic Level Up Shifting using HC04

As I said earlier, different approaches have different pros and cons, and you need to make an engineering tradeoff, or cost benefit analysis. If you wish to control 128 relays placed far far away, I2C MCP23017 is good; if you want to Mux/OE (Output enable/disable) the relay modules, then HCT125 is good; if you wish to up shift to different levels (not just 3v3 to 5v0, but 3v3 or 5v0 to 12/24/36V, then HC04 Quad Open Drain NAND gate is good. I tried HC04 the other day for a 817c photocoupler driven relay module and found it working OK.

HC04 up shifter

Up shifter using 2N2222

And if you want to entertain only one relay module, then the 4 shifters in 1 chip HCT125/HC04 is a waste or overkill. Then you may consider single transistors (such as BJT NPN 2N2222, MosFet 2N7000). I tried 2N2222 the other day and found it OK.

2N2222 up shifter

DIY your own module using 2N2222

If you are a DIYer or maker, and you want to build everything yourself, then you can use a Songle or

How does an Electric Relay work?


Built Your Own 5V Relay Module [using 2N2222, driven by rpi] - Nick Momrik 2017jul05



/ to be continued, ...

  • It might be more helpful to suggest one or two of the many ways to level shift up your GPIO's 3V3 level signal to 5V0 level, preferably one that has worked for you – scruss May 5 '18 at 14:35
  • @scruss Ah, there are more than 10 types of logic level shift up circuits out there. I can show you a few and let you select. Actually there are many sort of engineering trade offs you need to make, say are you using only one relay for the whole project, or 64 relays later. Do you place you relays near your rpi, or you prefer to use a 20m i2c cable and place the control part in the garage, etc. – tlfong01 May 5 '18 at 22:44
  • So what circuitry did you use to get it to work with Raspberry Pi? The level shift is the part the OP needs – scruss May 5 '18 at 22:53
  • This has nothing to do with the Pi and little to do with the question. To quote from the Tour "This site is all about getting answers. It's not a discussion forum." – Milliways May 6 '18 at 5:04
  • @Milliways, it has a lot to do with the Raspberry Pi: level shifting for relays is a common topic here, and it hasn't been adequately answered before. – scruss May 7 '18 at 13:02

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