Wednesday, 5 December 2012

Remote Controlled Eight-Relay Board


- Eight-Relay Module

I am making a remote control device. It allows me to independently switch eight relays and control various  items. When I press buttons on a small keypad, instructions will be decoded and transmitted via a microwave RF packet transceiver (@868 MHz). At the other end (up to 100m away!)  another transceiver decodes the message and switches the relays ON or OFF.

I used a relay module identical to the one in the picture above. It's an optically isolated 8-relay module. That's nice because it makes controlling it easy with an Arduino.  It's worth while reading these links before starting:

I didn't need full isolation, so I kept the Vcc and JD-Vcc pins connected using the jumper on the board. I wouldn't use more than 4 relays working at once in my Firework firing RC device. If you intend to use more than four relays at once, then you need to use a separate power supply for the relay coils (see Optically isolated 8-relay module instructions). This is because the 5v supply can be damaged by the current needed to operate all at once (8 x 80mA = 640 mA ). 

You can use a separate 5v supply for the relays, so long as that supply is capable of more than 640 mA. [NB USB should not exceed 500mA].

If you require a separate power supply for the relays follow: Optically isolated 8-relay module instructions with respect to the JD-Vcc jumper and ground connections

Quick-test of the module
Before playing around with code, I wanted to check the relay-module was firing all the relays and they were doing what they were supposed to do - ie switch stuff on and off. The designers of the board  thoughtfully provide a diagram of the NC and NO circuits alongside the screw-terminal triplets:

The circuit I need is common (C) and normally open (NO), so when the Arduino fires the relay it switches power from OFF to ON and a device comes to life e.g. a light bulb, or in my case, a firework igniter.  

Relay Module - a single relay firing circuit in action (click You-tube to view).

These modules fire when a relay-control pin is taken low e.g. to 0v or ground. So, to test all eight relays in turn, I connected the Arduino 5v pin to the Vcc pin on the relay module and the GND pin to Arduino GND.  

I used another Arduino ground wire to touch each control pin on the module (IN0 to IN7) in turn. I got nice clicks as they fired to make the NO circuit, and led indicators coming on - great! By replacing the bulb on the circuit above with my voltmeter I got 12v switched on the relay screw-terminals. [NB using C and NC would work the other way around].

So, relay board tested and working - time to work on some Arduino code!



  1. We hope you are on track to start the fireworks on your birthday. Post some pictures of the great event!

    1. Thanks for the comment. I'll post a video a couple of days after 12th Dec.