Hello All,This thread has been very useful. I am not sure about one thing - for a 110vAC fan control circuit do I need to use the transformer to get 12V-0V-12V or is there a way I can use the AC supply directly into the optocoupler to drive the MCU. I believe I saw a schematic snap shot which shows AC supply connected directly to OC and then OC talking to the MCU. Thanks.
Hi,Yes but what is strange is i have seen people do this and it does vary the speed and works for quite some time. Motors with brushes do work better as far as i know like with power tools.Good AC drives change the voltage AND the frequency.I use a DC fan for low speed myself.
universal AC motor does. and it is more than likely that a fan will be equip with it.
Speed controlContinuous speed control of a universal motor running on AC is easily obtained by use of a thyristor circuit, while multiple taps on the field coil provide (imprecise) stepped speed control. Household blenders that advertise many speeds frequently combine a field coil with several taps and a diode that can be inserted in series with the motor (causing the motor to run on half-wave rectified AC).
It could be pretty messy if you try to directly interface the Arduino with 110 Volt (or worse 220V) power. There are all kinds of electrical hazards that can be created, and you definitely risk the destruction of your microcontroller.If I were doing this, I would get a TRIAC fan controller (most hardware stores) which has a circuit similar to one shown in post #2. Then replace the speed control pot (has the knob on it) with a photoconductive cell (Mouser or Digikey) optically tied to an LED (put them in a little tube - one on each end). Apply your PWM signal to this LED to control its brightness and in turn that controls the resistance of the photoconductive cell and the fan speed. There is no direct electrical connection to the 110 or 220 Volts (make sure the two leads to your LED don't touch anything in the fan controller). Size the resistance of your photoconductive cell to the maximum resistance of the speed control pot you remove.As the value of your PWM variable increases, and so the duty cycle of the LED, the photoconductive cell resistance will decrease and the fan speed will increase. It will act just like the speed control but your microcontroller will be in charge.
When you say "photoconductive cell", are you referring to a light-dependent resistor or a photodiode?