I need to control fan speed digitally via an app or Blynk while retaining the analog pot that allows speed control.
Its an AC fan for a fireplace.
Are there any options like that?
How is the fan speed currently controlled?
With a physical pot.
Are you sure?
Normally it's by PWM
So its actually a Rheostat, basically this https://www.amazon.com/Hongso-Fireplace-Variable-Rheostat-Control/dp/B01JL1GACK
What’s Blank?
Is it a dyslexic Blynk?
Autocorrect got the best of me. I meant Blynk.
you can get fan speed control module that can be controlled by arduino’s PWM and use pot or rotary encoder to control arduino
Sorry, your link doesn't work for me.
It's actually not a rheostat. It's a triac based AC motor controller.
Really? Why do the manufacturers call them Rheostats?
Because they don't want to miss sales to people who mistakenly call them rheostats. Many people will search for "fireplace rheostat" on Amazon because it's what their uncle or someone calls it.
Interesting, hopefully someone has some input on having both digital and analog control options.
There are a couple of issues with a digital pot in a "standard" dimmer or motor control circuit... Some may not handle negative voltages (so they don't work with AC), they generally can't handle 120V or 240V, and the Arduino (or other control circuitry) needs to be electrically isolated from lethal voltages.
AC light dimmers use Phase Control to turn-on power during part of the AC cycle. I believe AC motor control works similarly, but there may be some differences and some motors may not be speed-controllable this way. (I've made a dimmer but I've never made a speed control.)
You can find Arduino dimmer projects - An opto-isolator is used to detect the AC zero-crossing and another special TRIAC opto-isolator drives the main TRIAC which controls the dim-level.
There is a delay after the zero-crossing and then a trigger is sent to the TRIAC. A TRIAC latches-on after it's triggered and it stays-on until current drops to zero (at the next zero crossing), So a short delay makes the light bright and a longer delay makes the light dim.
How is that supposed to work? Are you going to have a switch? It would have to ignore the knob setting or ignore the digital signal, so you could do that with a switch.
Or, you could use a rotary controller (which goes round-and-round) or you could have "up: & "down" buttons. In those cases the rotary controller or buttons would be inputs to the software so the software would remain in control.
My home automation dimmers (which I didn't build) have center-off rocker switches so you can operate them locally or remotely and the brightness just depends on the latest local or remote command.
The speed control on AC motors only work on the so-called AC/DC motor. Those have the field coils and the armature in series. Those are low power motors, like old electric drills, etc.
Its a pretty small ac fan for a fireplace.
But it has taken 18 posts to find this out.
When I read the topic originally, I thought it was something like a cooling fan in a computer
Sorry, I did leave out an informative piece of information. I've edited the original post.