5 V relay connected to Arduino

Question

I have a 5 V relay module connected to WeMos D1 board. The load is a small electric cooker.

The code turns on and off the relay every 5s for testing purposes.

digitalWrite(pin,HIGH); delay(5000);

digitalWrite(pin,LOW); delay(5000);

However, the green light and red light are always on. there is no switching happening. An onboard led on the WeMos D1 board is blinking every 5s.

Relay specs: https://www.ebay.com/itm/2PCS-1-Channel-DC-5V-Relay-Switch-Board-Module-for-Arduino-Raspberry-Pi-ARM-AVR/383693511233?_trksid=p2504926.m5232.l9681

int pin = 14;
void setup()
{
  pinMode(pin, OUTPUT);
  
}


void loop()
{
     digitalWrite(pin,HIGH);
     delay(5000);

     digitalWrite(pin,LOW);
     delay(5000);
}

Thank you!

Answer 1

It's very difficult to tell from the poor quality images posted but it appears that you may have connected the wires on the left side of the board one pin out of position.

Figure 1. The relay module requires 5 V so it should be powered from the 5V pin on the WEMOS board. The relay module GND should be connected to any GND pin on the WEMOS.

Figure 2. Connections on the relay board are unclear. Here it appears that you have connected in sequence red, yellow, black. This doesn't match the colours on the WEMOS.

Note the order on the relay module is VCC, GND and IN.

^{simulate this circuit – Schematic created using CircuitLab}

Figure 3. Wiring diagram.

You expressed fear of circuit diagrams in your original post. There is no need to fear them. They are the simplest unambiguous way to show the scheme of the circuit. You can see that in this case it's ridiculously simple to understand.

There should be no connection between the WEMOS and the mains wiring other than the through the isolation of the relay.

Answer 2

• make sure your 3 wire interface uses a common ground with relay coil and logic supply
  - Make sure you are using 5V and not 3.3V for the 5V coil
• if it is good code then the voltages will switch on the interface which you can easily measure or use 1k R+LED as a crude logic probe.

Since the 3 wire interface is low current it is better to use twisted pairs of AWG24 CAT3 or similar for EMI reasons and neatness rather than 16 or 18 AWG

Answer 3

Deactivating a relay requires conditionally activating a 20K resistor (PULLUP) on the Arduino board.

const byte pin = 2;

void setup(){

  // Define the pin as INPUT_PULLUP until you are ready to use it.
  pinMode(pin, INPUT_PULLUP);

}

void loop(){

  delay(1000);

  // Activate the relay. Supplying a low impedance
  // path to ground turns the relay on.
  pinMode(pin, OUTPUT);
  digitalWrite(pin, LOW);

  delay(1000);

  // Deactivate the relay.
  pinMode(pin, INPUT_PULLUP);

  // Using digitalWrite(pin, HIGH); is an alternative to using
  // pinMode(pin, INPUT_PULLUP); If your relay module is the
  // same as the one shown below, then it doesn't matter which
  // method you choose.

}

Answer from VE7JRO

About INPUT_PULLOUT on Arduino boards