horrible interference - subwoofer controlled by arduino if digital poti

Projects General Guidance
1

Hi,

my arduino controlls my subwoofer by:

  1. a relay for the subwoofers power
  2. a digital poti for the volume level

Problem:
There is a lot of interefernce as soon as I connect the arduino to a AC power supply.

Observation:
If Poti is set to MEDIUM (25KΩ) the interference is low. If POTI is set to min or max (0KΩ/50KΩ) the interference is horrible.

This is my Setup:

many THANKS!

Petz

2

Is that little green thing an AC-DC converter?

Is that the cause of the problem?

Does the Arduino work OK from a battery?

...R

3

One reason that fritzing is disliked here is that people often use substitute parts and it makes it impossible to read.

However it seems you have no decoupling capacitors at all.
Also neat wiring helps minimise pickup.

4

If it's not the power supply, are you clocking the digital pot continuously? If so, try modifying your code so that no digital signals go to into the pot once it's set.

If none of that helps, you'll probably have to isolate the Arduino in a metal box.

5

Ok - have to check why I get no reminder if there is a response to my topic :wink:

So let's see:

  • Everything works fine when Arduino is powered by my Laptop (battery)

  • The AC-DC Converter could be the problem, but I also tried USB power supplys (e.G. Apple iPhone) and that changes nothing. Still a lot interference.

  • Fritzing: I thought the circuit is straight forward... sorry

  • pot is set once... unfortunately...

  • neat wiring... ok, I can work on that one :wink:

Many Thanks for all your help!

6

this is probably something called a Ground Loop, indicated by the fact you don't have the issue when you power via a battery

there are various solutions, look up ground loops in google for more info