esp tinkering#2 controlling a fet

After the pir ride i’ve added the dht - that worked without any issues; the biggest problem was that i was sure i’ve connected it to gpio4…and in reality it was connected to 5…I now have large ESP12E module layout printed out - this will probably prevent mistakes like this.

The fet needs pwm control…so I wanted to continue with that.

Wiring it up was not much an issue.

At first i’ve used the analogwrite function to pwm control the fet - after some loose wire issues I was able to do it….

However…there was a problem:

There was some flickering sometimes when the module read the dht&sent the mqtt packet …

I’ve digged into this pwm thing…and it looks like its pretty limited how can someone do pwm with this chip - basically there are only some basic timers…which will fire sometimes - with some possible jitter.

I’ve found a library which promised better pwm results…but I was not yet able to make it work..


I’ve looked into utilizing Timer1 -after some tweaking I was able to run an interrupt function at 15khz…but the flickering remained.

Now that i’m writing this…i’ve puzzled together some theory…

my known facts:

  • flickering happens when the esp reads the dht
  • timer interrupts are jittering

So I suspect that the chip itself can’t kick out the main thread from execution…

Few days have passed…

I’ve tried various methods to remove the flickering - the most ridiculus was: when I enabled nmi for timer1… after that I was not able to push ota updates to the device… :)

I’ve decided to simply just give up on handling this on the esp….it doesnt have hw pwm - which is a must for me.

I want dedicated hardware pwm!

So…i’ve looked around: how to provide pwm some other way….i’ve digged into various kinds of power pwm ics (for those to work; I guess that I would need some digital resistor..) and other options…. like employing a small mcu for the task (like an attiny).

I’ve looked for a solutions which maximizes the objectives:

  • pwm is a must
  • minimal footprint-
  • i2c or spi support
  • cheap ;)

After considering a few options I’ve choosen attiny85 for the task.

attiny86 for the rescue!

I had a single attiny85 board at hand - i’ve checked the schemantic; it had direct access to the chip, so its great.

After a couple hours of hacking.. (eclipsearduino doesn’t handle attinycore board out of the box correctly - so i had to fix that ;)…

I was able to load some blink++ to that board; i’ve loaded the ‘production fw’ into the chip: i2c read => analogwrite.

Final touches

Hooking up with the esp was - as always - a bit problematic….wdt resets/etc - but after connecting the right wires to the right pins: I was able to control the fet using mqtt - without any flicker…and I’ve at least 2 possibly usable pins left on the tiny!


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