# Replace some LEDs with diodes in relay circuit

I need to know if I can replace the input LEDs (IN1, IN2, IN3, IN4) by a diode or resistor and if this can help me to reduce the voltage consumption generated by these LEDs.

The circuit is a 4 relay module for use in Arduino and RPi projects. I have this module connected to my RPi, but the RPi show me a "LOW POWER" message when I connect the module to GPIO pins. The RPi is powered with their appropriate power supply.

(*) All pics taken from SUNFOUNDER. For more info about the relays module visit SUNFOUNDER.

• What do you mean by 'Low Power Message' ...do you mean the lightning warning on the display? – Jack Creasey Apr 21 at 5:16
• Why, why, why do the companies that make these things put optocouplers in the circuit, but then connect the grounds? If the grounds are connected, there's no point in the optocoupler. If you need the isolation provided by the optocoupler, then you shouldn't connect the grounds. Cargo cult design, I guess. – JRE Apr 21 at 9:16
• grounds are not connected in this circuit, than the supplies can be separated by jumper. – Jasen Apr 21 at 12:17
• there's no way that's going to overload the 2.5A raspberry pi power-supply, you're doing something wrong with the wiring. – Jasen Apr 21 at 12:21

If you are unable to power the relay module with Raspberry Pi (i.e. the relays do not switch properly), it is because the module requires 5V input but RPi GPIO can only output 3.3V.

This problem can be solved by powering the relays with external 5V voltage source.

The Low Power message is due to the relays drawing quite a lot of current from RPi power supply. Removing the LEDs won't solve the problem as those LEDs don't consume much current.

• Hi @Electric_90, thanks for reply. I'm using external power supply in the relay module and the RPi only for signal, however the RPi shoe me the "LOW POWER" message when I connect the relay module and the LED's turn on. – Edward Navarro Apr 21 at 4:30
• Can you confirm that the RPi is being powered with appropriate power supply (i.e. 5V, 1A or more) and your connections are as mentioned above. Try using a beefier 5V power supply (somehing like 1.5A - 2A) for RPi. – Electric_90 Apr 21 at 4:33
• Yes, the RPi is being powered by a 5V-2A power supply and the connections are as mentioned above. – Edward Navarro Apr 21 at 4:36
• @EdwardNavarro, Removing LEDs will save power but not enough to create an impact on the performance. Try checking the RPi input voltage with a multi meter whether the voltage actually drops or not. – Electric_90 Apr 21 at 4:44
• The relays DO NOT draw power from the R'Pi )or Arduino) GPIO. The GPIO sinks current from the relay power supply. – Jack Creasey Apr 21 at 5:47

Removing the LEDs won't really help. The optocouplers require a certain current through their LEDs to turn on correctly. The manufacturer of the board will have designed it so that the combination of a 1K resistor and an external LED results in the correct current.

You could replace the LEDs with resistors. But you would have to choose resistors that give the same current as before. The end result is just as much current draw, and no indicators to tell you which outputs are on.

assuming that by their appropriate power supply you mean this one: https://www.raspberrypi.org/products/raspberry-pi-universal-power-supply/ that should have plenty of power to spare for 4 relays.

so I'm guessing you're trying to operate the relays of 3.3V. this may kind-of work, but the raspberry pi probably can't spare enough current from it 3.3V source

Connecting the VCC to +5V seems wrong as the GPIO is not 5V tolerant. but the optocoupler will drop about 0.9V and the LEDs will drop about 1.6V so the voltage seen at the GPIO will be well within the range allowed.