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Dan Nixon

Code Monkey, Electronics Engineer, Mad Scientist.

Play radio (almost) full testing

By Dan Nixon on 2013-03-06

I have spent a lot of time today testing my electronics for my Google Play Radio project and am glad to say that it is pretty much done. This is the first time I have had a chance to test every section of the electronics together (with the exception of the DC-DC converters, I would have had to kill the WiFi in the flat to get a 12V power supply) and was surprised to find as few problems as I did.

However there were several issues:

  • There was a lot of noise and interference from the amplifiers, however most of this was fixed by keeping the signal path as short as possible (it was very long to start with) although this should not be a problem of the final item. I also modified the code to ensure that for as much time as possible the amplifier is kept powered off when no audio signal is being produced by the Pi, this helped to cut down on pops between tracks and low pitched hum and a little bit of high pitched noise that was able to be heard when no song was playing.
  • My volume manager and LCD backlight code was broken, I fixed it.
  • I cut back on the amount that was printed to the console during operation, this was useful for debugging but now seems to slow the Pi down a little.
  • Fixed a problem with excessive power draw from transistors controlling the LCD backlight and amplifier power relay caused by incorrect resistor values, cut current draw by around 400mA.
  • Fixed a strange problem where after powering up the amplifiers after a volume value had been set using the digital potentiometers, little sound would be heard until the value was set again, I am still not sure what causes this but avoided it by setting the volume 0.25 seconds after the amplifier relay is turned on (gives the amplifiers a chance to power up).
Entire testing setup

Entire testing setup

Main electronics

Main electronics

Audio wiring

Audio wiring

Hopefully this project should be completed some time over Easter or Summer, depending on how long the PCB production takes and when I can get around to making the enclosure.

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