Electronic – Reducing electrical noise induced from a small DC electrical fan


What's a canonical method for reducing / eliminating electrical noise induced in ADC from a small brushless DC fan? For reference below, I'm also using this wall-wart and this 5V linear regulator.

My baseline system looks like this:

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I have some options in my head and I'm wondering what the best one might be.

My first idea is this [OPTION A]:

enter image description here

My second idea is this [OPTION B]:

enter image description here

My third idea is this [OPTION C]:

enter image description here

There are probably other options that I haven't thought of, as well as permutations and combinations of these options. What are the merits and drawbacks of these options? What option would you choose and why?

Best Answer

You need to decide how the interference is getting to your ADC input. The best way of dealing with the problem is at the source of the problem. The problem could be: -

  1. radiated EM emissions from the fan - try moving it closer or further away
  2. radiated EM emissions from the wiring to the fan - try moving the wires closer or further away
  3. conducted emissions from the fan/wiring causing power supply problems such as upsetting the ADCs voltage reference
  4. Bad practice on laying out the circuit board such as ground and power currents to the fan also sharing copper with sensitive inputs.

These are just a few and until you resolve what is wrong and where it is wrong, asking for canonical solutions is premature.

There may be several solutions, all of which will work with any of the pictures in your question and these might involve: -

  1. Redoing the PCB layout to avoid shared copper for power and signal
  2. Adding decoupling caps to various places
  3. Using balanced measurement techniques on the ADC
  4. Improving wiring and adding shields
  5. Ferrite beads and clamps.

Work out what is causing the problem first and why.