8 channel I²C relay module board

description

8 channel relay module board with an I²C connection
control utility and example script for Raspberry Pi and Linux, with source code
comes with example code for Arduino
up to 8 boards can be connected to each I²C bus
each board can be assigned an I²C address between 0x20 and 0x27 by the DIP switch SW1
removable terminal blocks for easy assembly and disassembly
relays with SPDT switch contacts: Normally Open, Common, Normally Closed
separate power input for the relays to avoid glitches on the power lines of the digital circuits
LED indicators for each relay
relay power input reverse polarity, overvoltage, overcurrent protection, LED indicator

Board connectors:

5.5/2.1mm DC jack female connector for relay power input, center positive (CN22)
2x4-pin 2.54mm pitch connector for logic power input and control connection (CN21)

Board size	100 x 80 mm (3.94 x 3.15 inch)
Logic supply voltage	3.0-5.5VDC
Relay supply input current required for 5V relays	635 mA
Relay supply input current required for 12V relays	267 mA
Relay contact ratings, resistive load	7A 28VDC 10A 125VAC 7A 240VAC
Relay contact ratings, inductive load	3A 120VAC 3A 28VDC
Relay contacts maximum voltage	250VAC 110VDC
Relay contacts resistance, ON	100mΩ max
Terminal block wire range	AWG24-AWG12

Setup and use

Connect CN21 to the logic power supply and the I²C bus
Connect a power supply to the relay power input jack CN22 (5VDC or 12VDC, depending on the relay voltage of the board)

The I²C module board connects to the master device with connector CN21. The pinout for CN21 is:

CN21 pins	pin name
1A, 1B (square)	VDD (logic power supply input)
2A, 2B	GND (common power supply ground)
3A, 3B	SDA (I²C data)
4A, 4B	SCL (I²C clock)

Connect the relay board to a Raspberry Pi as:

Raspberry Pi P1 pin	relay module CN21 pin	pin name
1	1 (square)	+3.3V (logic power supply input)
9	2	GND (common power supply ground)
3	3	SDA (I²C data)
5	4	SCL (I²C clock)

Connect the relay board to an Arduino as:

Arduino pin	relay module CN21 pin	pin name
power 5V	1 (square)	+5V (logic power supply input)
power GND	2	GND (common power supply ground)
analog 4	3	SDA (I²C data)
analog 5	4	SCL (I²C clock)

The logic power supply voltage should match the voltage levels on the I²C bus. The SDA and SCL lines are pulled up to VDD with 47k resistors on the relay module. The module contains an MCP23008 chip, please check the datasheet for the details.

Download the support package with examples and utilities for the I²C relay board. The package contains:

bin/linux.x86/relayctl	relay control utility for 32-bit x86 Linux
bin/raspberry/relayctl	relay control utility for the Raspberry Pi
src/arduino/relayboard_i2c.ino	example source code to control the relay board from an Arduino
src/i2c-tools/relayboard_i2c.sh	example shell script to control the relay board by Linux i2c-tools
src/relayctl/	C source code for the relay control utility

Example of controlling the relays on a Raspberry Pi board:

command line example	explanation
relayctl setport 0	turn all 8 relays OFF
relayctl setport 0b00001100	turn relay for CN3 and CN4 ON, all others OFF
relayctl setbit 0b10000000	turn relay for CN8 ON, don't change the state of other relays
relayctl clearbit 0b01000001	turn relay for CN1 and CN7 OFF, don't change the state of other relays

Using the relayctl utility

Usage: relayctl [options] <command> [value]
Control the relay board

 -b, --bus <I2C bus>
    Use the given I2C bus to access the relay board, default=/dev/i2c-0
 -a, --address <I2C address>
    Use the given I2C address to access the relay board, default=0x20
 -o, --output <base>
    Set output format. Base x=hexadecimal (16), b=binary (2), d=decimal (10), default=x
 -v, --verbose
    Verbose mode
 -V, --version
    Show program version
 -h, --help
    Show usage and help

The commands are:

command line	description
relayctl getport	read the actual state of the relays. Command output is an 8-bit number <n>
relayctl setport <n>	Set all 8 relay states in one instruction. Use bit value of 1 to turn a relay ON, 0 to turn a relay OFF <n> is an 8-bit number
relayctl setbit <n>	Turn the selected relays ON. Use bit value of 1 to select relays to turn ON <n> is an 8-bit number
relayctl clearbit <n>	Turn the selected relays OFF. Use bit value of 1 to select relays to turn OFF <n> is an 8-bit number

Numbers for <n> can be given in decimal, hexadecimal or binary format. Hexadecimal numbers are prefixed with '0x', binary numbers are prefixed with '0b'. Command output base can be also set to hexadecimal with switch -ox, decimalwith switch -od or binary with switch -ob.

The mapping of <n> to relay contacts is:

relay contacts	CN8	CN7	CN6	CN5	CN4	CN3	CN2	CN1
bit position	bit#7	bit#6	bit#5	bit#4	bit#3	bit#2	bit#1	bit#0
bit value in HEX	0x80	0x40	0x20	0x10	0x08	0x04	0x02	0x01
bit value in decimal	128	64	32	16	8	4	2	1
bit value in binary	0b10000000	0b01000000	0b00100000	0b00010000	0b1000	0b0100	0b0010	0b0001

Examples:

command line example	explanation
relayctl getport	read the actual state of the relays. The output value is an 8-bit number, where a bit value of 1 means that the corresponding relay is ON, a bit value of 0 means the corresponding relay is OFF. Command output is: 0x01 (relay for CN1 is turned ON, others are OFF)
relayctl -od getport	read the actual state of the relays. Same as the previous command, but the output is printed in decimal. Command output is: 1 (relay for CN1 is turned ON, others are OFF)
relayctl -ob getport	read the actual state of the relays. Same as the previous command, but the output is printed in binary. Command output is: 0b00000001 (relay for CN1 is turned ON, others are OFF)
relayctl setport 0	turn all 8 relays OFF
relayctl setport 12 or relayctl setport 0x0c or relayctl setport 0b1100	turn relay for CN3 and CN4 ON, all others OFF
relayctl setbit 128 or relayctl setbit 0x80 or relayctl setbit 0b10000000	turn relay for CN8 ON, don't change the state of other relays
relayctl clearbit 65 or relayctl clearbit 0x41 or relayctl clearbit 0b01000001	turn relay for CN1 and CN7 OFF, don't change the state of other relays

Using i2c-tools or the example shell script

1. Install i2c-tools

yum install i2c-tools # pidora
apt-get install i2c-tools # raspbian

2. Find the I²C buses on the master:

i2cdetect -l
i2c-0   i2c             bcm2708_i2c.0                           I2C adapter
i2c-1   i2c             bcm2708_i2c.1                           I2C adapter

3. Scan the buses for the relay module address:

i2cdetect -y 0
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: 20 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

i2cdetect -y 1
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

The relay module address was found on the i2c-0 bus with address 0x20 (setup with SW1). The bus number (0) and address (0x20) detected will be used in the following steps to select the relay module.

4. Set the MCP23008 IODIR register to zero:

i2cset -y 0 0x20 0 0 # IODIR

5. Set the MCP23008 OLAT register to control the relays:
i2cset -y 0 0x20 0xa 0xff # OLAT, all relays ON
i2cset -y 0 0x20 0xa 0xf0 # OLAT, turn CN1, CN2, CN3, CN4 OFF, CN5, CN6, CN7, CN8 ON
i2cset -y 0 0x20 0xa 0x00 # OLAT, all relays OFF

Mechanical