Bluetooth noise through input

[Hayden]

Hello,
I was wondering if anyone knows of this issue.
Items I have:
Laptop power supply 19V
DC to DC converter that steps down 19v to 5v to run the Bluetooth module
USB powered Bluetooth module
2.1 ch audio amplifier

As in the video firstly it is fine when I have the Bluetooth module connected to the DC to DC converter with an auxiliary cable connected and it is great but when I disconnect the aux cable the noise is amplified a ton!!! Then I swap from the DC to DC converter and plug in a mobile phone charger to power the Bluetooth module and it goes away.

This is the video of the issue: https://www.youtube.com/watch?v=lbRkYyXWOxE
Is this a grounding issue?
Or would ferrite sleeves work?

those links are to the bluetooth adapter i have and the dc to dc converter
https://www.jaycar.com.au/arduino-compatible-dc-voltage-regulator/p/XC4514

https://www.jaycar.com.au/medias/sy...dongle-with-transmit-receiveImageMain-300.jpg


Any suggestions would be so greatly appreciated

 

[sgrossklass]

You have stumbled into about the same grounding issue that approximately a million people before you have. If you draw up a plan of power and signal grounds, you will find at least one loop.

Want an easy solution? Use a dedicated 5 V wall wart (but preferably not the $2AUD with shipping from China safety hazard kind, those watching Big Clive's YT channel should know why).

 

[Pano]

I went around and around and around with the same problem recently. There was no grounding scheme that killed the noise. The only thing that killed the noise (and well) was galvanometric isolation.

If there was a transformer between the amp and the BT module, all was quite. This could be done by either using a separate 5V SMPS for the BT, or inserting isolation transformers into the left and right audio lines. Obviously the later was expensive.

Here's what worked for me.
I used an isolated DC/DC convertor. CRE1S2405SC from Murata. That part drops 24V to 5V, so you will need to find a version for 19V to 5V. Cost about $4 each and works like a charm. I did use their suggested LR filter on the output.

If you can't sort out the grounding problem, try the isolation.