Unstable analog readings with Teensy 4.1 and 74HC4067 multiplexer

B

Bakhanbeigi

Member
I’m working on an audio project using a Teensy 4.1 with the Audio Shield, and I’m using a 74HC4067 (16-channel analog multiplexer) to read multiple analog inputs.

Connections​

The mux-to-Teensy 4.1 connections are:
  • S0 → Teensy pin 19 (A5)
  • S1 → Teensy pin 20 (A6)
  • S2 → Teensy pin 21 (A7)
  • S3 → Teensy pin 22 (A8)
  • COM → Teensy pin 23 (A9)
  • VCC → Teensy 3.3V
  • GND → Teensy GND
  • EN → GND (always enabled)

Inputs​

  • C0–C4 → five 10k potentiometers
  • C5–C7 → joystick connector
  • C8–C15 → not connected

Problem​

I’m seeing unstable and inconsistent readings:
  • Sometimes values appear random
  • Occasionally channels don’t respond at all

What I want to verify​

Before I assume it’s a soldering issue, I want to confirm:
  1. Are these correct analog pins to use on Teensy 4.1 with the Audio Shield?
  2. Is there any known conflict between these pins and the Audio Shield?
  3. Could leaving unused mux channels floating (C8–C15) cause this kind of noise?
  4. Should I add pull-down resistors or buffering on the mux output?
If anyone has experience with Teensy + 74HC4067 in audio projects, I’d really appreciate your advice.

Thanks!
 
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