The audio signal coming from your music player needs a bit of massaging before it can be read by the analog inputs on the NeoTrellis M4. We'll build a small circuit using two capacitors and two resistors to remove the DC bias and center the incoming audio around the correct voltage for the NeoTrellis M4's analog-to-digital converter (ADC).

If you haven't already put together your NeoTrellis M4, follow these instructions on assembly.

This can be done on a breadboard if you like, but if you want to keep it small and mobile, you can do without, and go for a "dead bug" style of construction. These are the connections:

  • NeoTrellis M4 STEMMA connector green to first 10uF capacitor negative leg (the shorter leg, and the one with the white stripe on the body of the cap)
  • First capacitor positive (longer leg) to audio jack terminal block 'L' terminal
  • STEMMA connector green to first 10k resistor (either leg)
  • First resistor to audio jack terminal block GND

 

  • STEMMA connector white to second capacitor negative
  • Second capacitor positive to audio jack terminal block 'R' terminal
  • STEMMA connector white to second 10k resistor
  • Second resistor to audio jack terminal block GND

 

  • STEMMA connector black to audio jack terminal block GND

You'll find it easiest if you twist the legs of some components before inserting them into the STEMMA wire connectors as shown in this video. Just be sure that there are no accidental connections being made from the leads touching where not intended.

Plug the JST PH 4-pin cable into the STEMMA connector on your NeoTrellis M4 and you'll be able to read the incoming audio signal.

Next, let's flash the NeoTrellis M4 firmware with the filter/visualizer code.

This guide was first published on Dec 09, 2018. It was last updated on Dec 09, 2018.

This page (Audio Input Circuit) was last updated on Nov 28, 2021.

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