AC PWM FOR ESP8266 NodeMCU

Controlling AC Appliances with ESP8266: A Dimming Solution

This project focuses on achieving precise dimming control for AC-powered appliances using the popular ESP8266 V3 or NodeMCU microcontroller. The core of the AC voltage regulation lies in the implementation of a TRIAC, specifically the BT136 model. TRIACs serve as electronically controlled switches capable of handling alternating current, allowing for smooth adjustment of the power delivered to the appliance.

However, directly controlling the TRIAC with a microcontroller requires a crucial element: synchronization with the AC power signal. To effectively dim an AC appliance, the microcontroller needs to be aware of the zero-crossing points of the AC waveform. These zero-crossing instances, where the sinusoidal AC voltage transitions through zero, provide a reliable timing reference. By triggering the TRIAC at different points after each zero-crossing, the effective RMS voltage supplied to the appliance can be precisely controlled, thus achieving the dimming effect.

To safely and accurately detect these zero-crossing points, an optocoupler is employed. The optocoupler provides electrical isolation between the high-voltage AC circuit and the low-voltage microcontroller circuit, ensuring the safety of the ESP8266. It typically consists of a light-emitting diode (LED) on the AC side and a phototransistor or phototriac on the microcontroller side. When the AC voltage approaches zero, a corresponding signal is generated on the microcontroller side via the optocoupler.

Once the microcontroller receives the zero-crossing signal, it can then precisely time the firing pulse to the TRIAC. By delaying the firing pulse after the zero-crossing, only a portion of each AC half-cycle is allowed to pass through to the appliance. A longer delay results in a lower effective voltage and thus a dimmer output, while a shorter delay allows more of the AC waveform to pass, resulting in a brighter output. This method, known as phase-angle control, enables smooth and continuous dimming of AC appliances like lamps, heaters, and motors. The ESP8266's built-in Wi-Fi capabilities also open up possibilities for remote control and integration with smart home systems.