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Arduino Relay Control

Previously I have blogged about using relays with an Arduino, and SainSmart relays specifically. A while back I received a 4 relay, and a 8 relay board, and both of them used negative logic, i.e. a LOW activated them, and a HIGH deactivated them. Yesterday I received a single relay module as part of a kit, and found that this module uses positive logic, i.e. a High activates it, and a LOW deactivates it.

Being a 5v relay, it’s able to be driven directly from the arduino power. If you have a lot of additional hardware, you may want to consider a separate 5v supply, and common ground.

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We are printing the relay state to the serial monitor, but the LED on the relay board also signifies whether it’s active or not.

Only 3 pins are used, 5v (“V”), Gnd (“G”), and a data pin. We are using pin 7 in this example, and connects to the relay “S” (signal) pin.

Here is my test code:

void setup() {
// put your setup code here, to run once:
pinMode(7, OUTPUT); //don’t forget to declare the pin as output!

void loop() {
// put your main code here, to run repeatedly:
digitalWrite(7, HIGH);
digitalWrite(7, LOW);


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