Michael Michelotti
DC Fan Noise and the IR Receiver
DC Fan Noise and the IR Receiver cover image
When sensitivity meets noise
Updated: Mar 25, 2024, 12:00 AM

It was just another Tuesday when I decided on what would become my next embedded systems project. I knew I wanted to have some sensor drive some motor. In my innocence, I chose a TSOP IR receiver and a DC motor. The IR receiver would pick up a signal from an IR remote, then I would process that signal to control the fan. Perfect.

Excitedly, I got to work planning and developing.

It was all coming together. It was finally time to hook it all up, sit back, and watch the magic happen. I sat back and reveled in my creation.

IR remote fan initial setup photo

Looking back at this setup, I want to shake my innocent previous self and say:

Look at all these jumper cable antennas you have looping left and right. Where are your bypass capacitors?! You believe this will work. You sweet summer child.

I applied power and watched in horror as my receiver signal spiked and dipped uncontrollably 😱. Once I recovered from the shock, I hauled out my oscilloscope to see the damage.

Oscilloscope screenshot showing noise spike

Clearly, this would take some work.

Firstly, my Dr. meter DC power supply had a 160mV160\,mV ripple under no load at all. It’s got to go. Give me a nice clean 5V5V coming right of a wall wart. I replace the power supply. Power it up. Still no dice.

Alright, what if I twist the cables going to my motor? Surely that will cancel out some noise. I twisted them, to no avail. Maybe I’m out of my depth here. Maybe I should put up the SOS signal at eevblog.com.

The heroes who peruse that website came through big.

Feeling their collective hands on my shoulders, I got to work. I implemented an improvement, I tested. I implemented another, and tested again. Each time, the ringing looked just a bit better.

IR remote fan setup post mitigation

Finally, my IR receiver was happy. Finally, I turned on the fan. Alas, I’m still using cheap components on a breadboard, and thus the ringing remains. But hey, I can turn on the fan 😌.

Oscilloscope screenshot post mitigation

Project link