Arduino Relay Shield

This is a cheap relay shield for Arduino with four Relays. Relays are literally just electrically actuated switches, so you can connect them pretty much anywhere you would use a switch.

On the back side there is written:

CAIALEX
Relay Shield
V1.0
catalex.taobaocom

The relays are rated for 3A @ 120VDC or 3A @ 24VDC. Note that they are not rated for 240VAC, so won't be suitable for mains voltage switching in many countries.

Wiring

Simply plug the shield into your Espruino board.

The shield depends on the 5V line for voltage for the LEDs, so if connecting to a Pixl.js you'll need to short 5V to Vin when running off USB/LiPo power source. This can be done either with the solder jumper or just by connecting a patch wire between 5V and Vin on the Relay Board's header.

Software

These shields are extremely easy to use, so no code library is currently provided.

The relay board has the 4 relays connected to pins D4, D5, D6 and D7. If you write a 1 to a pin, the relay turns on, write a 0 and it turns off.

// Relay 1 on
digitalWrite(D4,1);
// Relay 1 off
digitalWrite(D4,0);
// Relay 4 on
digitalWrite(D7,0);

// Write to all relays at once...
// All on
digitalWrite([D7,D6,D5,D4], 0b1111);
// Relay 2 and 4 on
digitalWrite([D7,D6,D5,D4], 0b1010);
// All off
digitalWrite([D7,D6,D5,D4], 0b0000);

Buying

These Relay Shields are available on eBay, however many other versions of the same shield are available, and are often higher quality. For example Seeedstudio Relay Shield 3.0