Help needed with expression pedal input circuit

Hey,

I'm currently attempting to attach an expression pedal (essentially just a pot packaged within a foot switch) to an Arduino (well, a Teensy 3.6 which is a 3.3V Arduino-compatible board) using a switched 1/4" stereo jack.

I've tried wiring the socket using the most common wiring:

  • tip -> signal (analog pin on Teensy)
  • ring -> VCC
  • sleeve -> GND

This mostly works as expected, however when connecting the expression pedal jack plug to the socket the Teensy board resets, which I'm assuming is due to some kind of short circuit created in the process of connecting the jack.

I can prevent this from happening by instead using an alternative wiring where the tip and ring connections are swapped over (which my expression pedal can be set to support), however commercial expression pedal inputs using the most common wiring must overcome this issue somehow.

What would be the best way to prevent this from happening using the most common wiring?

Also I'm using a switched jack as I would like the Arduino to detect when a jack plug is connected, however I'm really struggling to understand how the switch (which is connected to the 'tip' of the socket when no jack is connected) can be configured and connected to the Teensy to do this.

How could I use the switch to detect a jack connection?

Many thanks.

Sounds like things are shorting out as you slide in the jack. The simplest way of stopping a short is to wire a 100R resistor in seriese with the 3V3 line. This might cut down slightly on the range you can get but you can easy compensate for that using a map statement.

liamtmlacey:
I've tried wiring the socket using the most common wiring:

  • tip -> signal (analog pin on Teensy)
  • ring -> VCC
  • sleeve -> GND

This mostly works as expected, however when connecting the expression pedal jack plug to the socket the Teensy board resets, which I'm assuming is due to some kind of short circuit created in the process of connecting the jack.

I can prevent this from happening by instead using an alternative wiring where the tip and ring connections are swapped over (which my expression pedal can be set to support), however commercial expression pedal inputs using the most common wiring must overcome this issue somehow.

What would be the best way to prevent this from happening using the most common wiring?

The 'best' way might be to use a short-circuit-proof opamp to generate the 3.3V sent to the pedal,
but that would require a higher voltage supply than 3.3V and a suitable opamp. Try the 100 ohm series
resistor as suggested - not quite the best! Perhaps a little larger if the 3.3V supply isn't very pokey.

I presume the footpedal is 5k or 10k linear or something like that. If its significantly lower in resistance
that might cause a rethink.