RLY08 -  8 Relay Outputs 
Technical Documentation

I2C mode
For serial mode click here




I2C Mode selection
I2C operation is activated when the mode pin is left open circuit.

I2C Operation
I2C Bus
The RLY08 is located on the I2C bus at a factory default address of 0X70. The SCL and SDA lines should have pull-up resistors on them somewhere on the bus. You only require 1 pair of resistors for the whole I2C bus, not specifically for the RLY08. They are normally on the master controller and you may already have them. If not, anything between 1k8 and 10k should work. I recommend 1k8 for best noise immunity. 

RLY08 register set
The RLY08 has only two registers, register 0 and acts as a dual purpose register. When written to it is the command register where all of the instructions from the commands section should be sent. When read it returns the software version. 
Register 1 is the relay register, when written to it allows the user to change all eight relay positions at once with a single byte. When the register is read it provides the current positions of the relays. If all relays are powered the register would contain 255 (1111 1111), all relays in the un-powered state would result in 0 (0000 0000)

I2C register set



0 Software version Command register
1 Relay states Relay states

Commands for I2C

decimal hex


100 0x64 All relays on
101 0x65 Turn relay 1 on
102 0x66 Turn relay 2 on
103 0x67 Turn relay 3 on
104 0x68 Turn relay 4 on
105 0x69 Turn relay 5 on
106 0x6A Turn relay 6 on
107 0x6B Turn relay 7 on
108 0x6C Turn relay 8 on
110 0x6E All relays off
111 0x6F Turn relay 1 off
112 0x70 Turn relay 2 off
113 0x71 Turn relay 3 off
114 0x72 Turn relay 4 off
115 0x73 Turn relay 5 off
116 0x74 Turn relay 6 off
117 0x75 Turn relay 7 off
118 0x76 Turn relay 8 off


Changing the RLY08 Address
To change the I2C address of the RLY08 you must have only one module on the bus. Write the 3 sequence commands in the correct order followed by the address. Example; to change the address of a RLY08 currently at 0x70 (the default shipped address) to 0x7A, write the following to address 0x70; (0xA0, 0xAA, 0xA5, 0x7A ). These commands must be sent in the correct sequence to change the I2C address, additionally, No other command may be issued in the middle of the sequence. The sequence must be sent to the command register at location 0, which means 4 separate write transactions on the I2C bus. When done, you should label the module with its address, however if you do forget, just power it up without sending any commands. The RLY08 will flash its address out on the LED. One long flash followed by a number of shorter flashes indicating its address. The flashing is terminated immediately on sending a command to the RLY08 and then becomes a power LED.

Address Long Flash Short flashes
Decimal Hex
112 0x70 1 0
114 0x72 1 1
116 0x74 1 2
118 0x76 1 3
120 0x78 1 4
122 0x7A 1 5
124 0x7C 1 6
126 0x7E 1 7

Take care not to set more than one module to the same address, there will be a bus collision and very unpredictable results.