I'm using Teensy 3.6 on a custom PCB as a midi controller, using 8 CD74HC4067SM96 Multiplexers
Daisy chained (4 and 4), so 2 analog and 2 digital in each chain.
I have a about 26 tactile push buttons on the PCB, all working fine, I created JST connection on board to connect external arcade buttons.
When an arcade button is connected it's value from the MUX is floating, randomly or I'm my hand are near the button or near the wire without clicking it.
I'm using the Internal pull-up resistor, this specific multiplexer is connected as shown in the attached schematic. - I don't have any issue with other buttons on this PCB which are connected to the same multiplexer, only with external wired buttons.. If I'm disconnecting the Button JST connector from the PCB the values are never changed and stable.
It looks like some interference related to the wires, the wires are short and about 24AWG, I can't seem to find the problem and need this thing to be stable urgently.
As I used almost all pins on the Teensy, this multiplexer signal line (M6) is connected to pin 13 with internal pull-up resistor on the Teensy 3.6 (which has an internal led on this GPIO).
Each external button is connected to GND and to a MUX pin (with internal pull up as I said).
Any idea please ?