Author Topic: Expression pedal optical switch replacement with potentiometer  (Read 660 times)

RyanOC

I have a Jimi Hendrix Experience pedal from DigiTech that I'm rehousing because the original housing broke into multiple pieces. I'm trying to figure out how to change the expression component which is comprised of what seems to be some type of optical switch. I can activate the expression by putting my finger over it and lifting it up and down. What I would really like to do is swap it out for a potentiometer and be able to mount that on a new case that I can activate with my foot. Can anyone tell me what exactly this component is and how I might be able to switch it out for a simple potentiometer? Thanks in advance


anotherjim

Re: Expression pedal optical switch replacement with potentiometer
« Reply #1 on: August 16, 2019, 10:06:03 AM »
I'm guessing it's an infrared emitter and receiver pair. It could be using pulse reflection - measuring the distance to "something" by the time delay from output to input. Not immediately obvious to me how to duplicate that with a pot in a simple way - and I'm only guessing that's how it works!
"Designing with PLLs in production circuits is reserved to those with the courage of the thoroughly uninformed."
Nuts & Volts
"Turtles have the short legs, not for the walking."
-Kenji "Damo" Suzuki

ElectricDruid

Re: Expression pedal optical switch replacement with potentiometer
« Reply #2 on: August 16, 2019, 01:43:03 PM »
Could be just an LDR.

<flashback>Back when I worked in the datalogging industry, we had a waterproof data logger product that had a LDR behind a clear plastic window to act as a button to wake it up. Putting your finger over the LDR and then uncovering it produced an event that the microprocessor could detect. It was a reliable system since it was all entirely sealed and had no moving parts. Those loggers could get totally submerged and still survive.</flashback>

anotherjim

Re: Expression pedal optical switch replacement with potentiometer
« Reply #3 on: August 16, 2019, 04:23:03 PM »
I think the round objects are only holes (weird optical effect makes them look like button magnets or something).
I suspect its U1 that's the active ingredient. It looks a bit like a naked optocoupler.
"Designing with PLLs in production circuits is reserved to those with the courage of the thoroughly uninformed."
Nuts & Volts
"Turtles have the short legs, not for the walking."
-Kenji "Damo" Suzuki