Remote Controlled Eight-Relay Board

PART III

- Eight-Relay Module

Introduction

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:

Using relays with Arduinos.

Optically isolated 8-relay module instructions

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!