What is it?

One way of control AC Power is through phase control with a Triac: the Triac then is fully opened, but only during a part of the sinus AC wave. This is called leading edge cutting. One could let an Arduino just open the Triac for a number of microseconds, but that has the problem that it is unpredictable during what part of the sinus wave the triac opens and therefore the dimming level is unpredictable. One needs a reference point in the sinus wave. 1) For that, a zero crossing detector is necessary. This is a circuit that tells the Arduino (or another micro controller) when the sinus-wave goes through zero and therefore gives a defined point on that sinus wave. Firing the Triac after a number of microseconds delay starting from the zero crossing therefore gives a predictable level of dimming.Then, you control power to 0% to 100%.

Why did you make it?

Because it is difficult to find this type of AC dimmer in Brazil. And it's an easy and inexpensive way to implement a DIY home automation. To connect dimmer and Arduino, you can use up to 100 meters of wire. Another trick is that you can send the control signal from the Arduino to the dimmer directly using a digital output (15mA/output at 5V).

What makes it special?

This dimmer is very small, 30mm x 30 mm. Can be used directly on the switch box of the electric installation. And you can use up to 10 mini dimmers in a single Arduino. But you must use a zero cross sensor attatched at Arduino ( https://www.tindie.com/products/JUNIOR700/zero-cross-module/ ), to sicronize all dimmers. If you want to use AC loads > 2A, please use proper heat sink.

STOP: This circuit is attached to a 110-220 Voltage. Do not touch this if you are not confident about what you are doing. Unplug it before coming even close to the PCB. The cooling plate of the Triac is attached to the mains. Do not touch it while in operation. Put it in a proper enclosure/container.

WAIT: Let me just add a stronger warning here: This circuit is safe if it is implemented only by people who know what they are doing. If you have no clue or if you are doubting about what you do, chances are you are going to be DEAD!DO NOT TOUCH WHEN IT IS CONNECTED TO THE GRID.

Zero Cross Sensor not included.