One of the goals in my previous timer project was to achieve the ability to control multiple electronic devices using the precise time signal generated by the RTC chip (bq3287). For electronic devices using up to a couple of amperes, a relay should be more than capable to handle the load. But for high voltage and high current home appliances such as water heaters (typically 240V, 20 to 30 A), the relay solution becomes much more expensive and less reliable. So I turned to a solution using an optocoupler-isolated TRIAC circuit.
This circuit uses a BTA41 TRIAC from ST Microelectronics as the main switching device. The optocoupler used to trigger the TRIAC is Fairchild Semiconductor‘s MOC3061.
Using the above circuit, the load can be easily turned on and off using an MCU’s output. Here is a picture of the control timer I built earlier and the control signal is outputted from the bottom:
