I’ve purchased a FEZ Domino board with the mp3 board extension. I’m trying to use them like a little mp3 player; to do this, I add to the project a little audio amplifier (connected to the headphone jack of the mp3 board) and a AC power supply to power all the system. When system start, I hear a lot of noise (it seems a noise originating from the clock generator or the main chip itself of the Domino board) and the only solution I find is use two separate power supplies, one for the Domino and one for the amplifier. If I connect a headphone to the mp3 board, no noise at all. What can I do (a specific power supply filter? have you a scheme for this?) to use the system in my configuration?
Thanks in advance,
You could try a “ground lift” hardware part.
When I did the technical part for festivals and bands, I rather often used them. Ground lifts are great to reduce noise and interference in audio hardware.
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A good mixed signal design will have analog and digital circuitry wired separately. Ideally, you would have a separate power regulators but you can also get the analog power through some ferrite beeds and add decoupling capacitors on each side.
Probably some 100nF capacitors will do the job…
after some investigation I have founded where noise arises; it isn’t originated by the Domino board but by the MP3 module itself (it seems noise related to the serial communication). To avoid this, I connect the ground of the battery housing(Yes, I know, no battery is required when using the MP3 module with the Domino!) to the general ground and, magically, noise goes away! Please note that I haven’t professional electronic equipments to investigate deeper, so get it only like a ‘try it… use it!’ :
Hi. General ground? ground of the fez or some gnd on the mp3 player? tia
Ok, this is my configuration: with the FEZ domino and MP3player I mount two DC power regulators (one for the FEZ and one for a little mono amplifier using a TDA7056 chip, both with the same ground, because I use only a AC transformer); that ground goes to the FEZ by the DC power supply and to the amplifier; if I don’t share that ground with the - of the battery housing I hear a lot of noise from the amplifier, if I connect that pin, the noise is greatly reduced. Please note that I use a 100n capacitor to block eventually DC voltage at the signal in of the amplifier and a 5K trimmer to adapt the amount of signal to the amplifier.
Thanks for the reply.