Relay module, CL1 relay 1 control, low relay / CL2 relay 2 control low relay ?


I just bought a 2-relay module.

From above it has CL2, CL1, DC- and DC+.

By using a 5V source I found that by connecting CL2 or CL1 to DC-, the relays closed. So there is no such thing as IN1 or IN2 that expect a HIGH signal from the board.

Will they work,i.e. make the relays work, at LOW? So I will put the pins to ground, I guess I should set them as INPUT_PULLUP and put them to LOW to make the relays work, am I OK or wrong?


Some relay modules are active HIGH, but most are active LOW.

It sometimes helps to write a HIGH to the pin (enabling pull up) before you set the pinMode, to stop the relay from chattering during bootup. Then use pinMode as normal. Don't use pin13.

in setup()
digitalWrite(relayPin, HIGH);
pinMode(relayPin, OUTPUT);

in loop()
digitalWrite(relayPin, LOW); // relay on
digitalWrite(relayPin, HIGH); // relay off