• Hardware

  • noise when charging Bela's 5v power pack supply from 12v battery

Hey there,
For a series of in situ installations I am using a setup (see picture down below) in which 8 channels from a Bela with an audio expander capelet are running through 4 stereo amplifiers which are powered by a 12v battery. The Bela is getting its juice from a 5v battery / power pack. The installations are running for 3 months outside, that's why I am charging the batteries from the 12v battery via a 12v-5v converter. But unfortunately this typical high pitched noise is popping up when charging the 5v battery from the 12v battery. I understand that it's better that the amplifiers and the Bela have separate power supplies, but this is difficult in the 7 different locations outside in which we place the installations. I have been trying some grounding approaches, but no luck so far. Would there be any way to get rid of such noise? Thanks in advance.

Look at the voltage on the 5V line when the battery is charging:

  • what DC voltage do you read?
  • with a scope, see if you are getting any DC ripple. If you don't have a scope, connect the 5V supply to Bela's analog input via a resistor divider, e.g.:
5V----+
      |
      R1
      |
      +---analog in
      |
      R2
      |
     _|_ GND

Using the same value for R1 and R2, in the range between 1k and 100k. Then look at the value on the Bela scope and see if there is some noticeable noise on it and what its amplitude is.