Many MCU applications use electro-mechanical relays to control AC loads. While this is an excellent solution for occasionally turning on/off a load, it is not suited for frequent switching or PWM applications. SSR1/A is an opto-coupled solid state relay that can control two AC loads in a arduino shield form factor.
Parts of this circuit are not isolated from earth ground and contain potentially lethal voltages. Never touch any part of the circuit when powered on.
Use a safety isolation transformer during experimentation and troubleshooting.
Always use a fues in series with the circuit to protect against short circuits.
- each channel can be controlled by a choice of arduino pins
- opto-isolated for safety
- uses either zero-cross (MOC306x) or random phase (MOC305x) opto-triacs
- optional triac snubber
For zero-cross switching use MOC306x type opto-couplers, for random phase switching use MOC305x opto-couplers.
Controlling the Relay
The board has 2 channels that can be controlled independently. Channel 0 can be controlled with Arduino pin 2,4,6,8,10 or 11. Channel 1 can be controlled with Arduino pin 3,5,7,9,10 or 11. The jumpers on the board allow the user to select which pin controls the respective channel.
The SSR1/A expect digital signals so the pins used for controlling the channels need to be configured accordingly. Assuming the jumpers are inserted for pin2 and 3 add to setup():
Then setting the output HIGH will turn on the load and setting the output low will turn off the load.
digitalWrite(2, HIGH); // Turns on channel 0
digitalWrite(2, LOW); // Turns off channel 0
To check the code it's not necessary to connect the AC. Each channel has a LED that will light up when the channel is turned on even if there is not AC connected.