using pwm on AC

I have been doing some research and I found a bluetooth device that is placed between a ceiling fan and house AC.

with the fan set on high and light on this device is able to control the light and basically dim the fan speed which I can only assume is done using pwm.

I suggested this a few months ago and I am pretty sure was told it won't work or it will be hard on the motor. Can you use an opto and triac with pwm to control the speed of the fan or AC power to other devices with pwm

I'll put a link to the device I found.....

bluetooth fan controller



That works very differently for AC. You can’t just PWM it.

It likely uses a triac to switch the AC, and uses a zero crossing detector to time what point in the AC cycle to fire triac (which will then conduct until the AC crosses zero).

Yes I am proposing using a zero crossing trigger opto with a triac

I am proposing using a zero crossing trigger triac with an opto triac driver

That is the standard approach and will work well.

[u]How Dimmers Work[/u].

Yes I am proposing using a zero crossing trigger opto with a triac

There are zero-crossing optical TRIAC drivers, but you don't want that! In order for dimming/speed control to work it has to turn-on some time after the zero-crossing.

The zero-crossing detection circuit is separate and it needs it's own optical or transformer isolation.

I've built a dimmer (a long time ago with another microcontroller) but I've never built a motor-speed controller. The schematics I've seen for inductive loads have a some extra components (a capacitor and maybe a resistor).

The schematics I've seen for inductive loads have a some extra components (a capacitor and maybe a resistor

I am reading the information you posted thank you for that.

but what you said sounds a lot like a snubber a resistor and capacitor


Well with just the ZC opto and triac pwm does not work.

I get either on or off pwm at 35 will not start the fan

pwm at 45 runs the fan at full speed.

Thanks Mark

Ok after a day of study it appears the easiest way to do this is with a chopper circuit I’ll post what I found below

I have attached a copy of the words and the circuit for easier reading…

I found a logic level IGBT is that what I need or a different one see below

link to IGBT

Now the diodes have names like D1 etc I don’t know a lot about diodes are the all the same I mean as long as they can handle the voltage???

I am assuming the 4n25 goes where the words VIN are

The article says this should work does anybody agree???

I found this diode the voltage is right the price is right

link to diode


Do you think it is a good idea to copy a circuit using diodes and connect it to mains AC when you “don’t know a lot about diodes”? Mains voltage kills! IMHO you should know very well what you are doing or you risk everything - including but not limited to damage to the electronics, fire and injury or death of you or someone else nearby. AFAIK by connecting mains voltage to neutral wire you may kill a neighbour who assumes the neutral is still neutral…
And I think 400V reverse voltage is low but I know little about mains. To be honest I wanted to use mains power directly some time ago. But after studying the topic I decided proffesional power supplies are not so expensive.

mtalent: it's 115VAC,

I prototype the whole thing using relays and tested system using esp8266 and mqtt.


Then I built one of the switches with the opto's and triacs and used it to run one setting (high on fan)

I ran that for a while and switched it on and off without problems.

Then built the board using the same switch setup only with 8 switches, 3 for speed control running through caps pack, one for light, 4 for H-Bridge to reverse motor direction.

this entire setup is just proof of concept will only ever be used and handled under experimental conditions by me only.

If I continue with project I plan to build board to UL specs. I have been researching these they don't sound too awfully hard but I will have engineer to help to fine tune equipment.

I just built this.

If you notice at the beginning this post it showed someone that was doing without getting into the fan but by intercepting the mains at installation, this got me thinking it must be PWM now after doing a tad bit of research I found that you either phase shift or chop. The phase shifting seems more difficult so I thought the chop was the easiest.

That is why I posted the above data about chop

Thanks, Mark

Hi there,

I found this post and I think you will be able to help me using this component

I read the doc "how dimmers work" on a previous post but I admit I have no idea how to use it with an arduino uno for example.

What I've understood : - Z-C pin allows opening or closing the gate using digitalWrite - with PWM pin I can then ask for a specific brightness value using analogWrite Is it that simple ?

Thanks for your help

EDIT : I think it is the same component as this one don't you think so ? And here is a code example