AC Dimmer for Arduino

Ever wanted to control a house lamp, a heater, a ventilator or similar 220/110 VAC equipment with Arduino? Here is a simple circuit that uses a standard AC Dimmer kit and controls it with an analog PWM output from Arduino. In this case a Vellerman-kit K8026 running at 220VAC. The kit has been modified, the potentiometer has been replaced by a LDR (Ligth Dependent Resistor) and C1 has been replaced by a 470nF for better adaption to the LDR range.



It works by leading the PWM output from Arduino through a lowpass filter made up by R2 and C3. This will stabilize the pwm to a steady voltage. The output from the lowpass filter is lead through an emitter follower to a LED, which is placed close to the LDR in a light conceiled compartment. The light from the LED then controls the resistance in the LDR.

This is a simple solution and requires no extra code in Arduino, but it has a few drawbacks. First of all it is not linear. This means that the usefull range is more narrow than the PWM output. Therefore you will need to find a suitable range for the Arduino output to operate. Second it has a little slow reaction about half a second, due to the lowpass filter.

NB! Always remember to be carefull with household power, and make sure that the left part of the circuit is totally isolated from the LDR and the AC Dimmer.