EV-2 Expression Pedal uses a log pot?

[fret]

So I bought an EV-2 a while back thinking it was a great physical design and nicely sized for travel. But it wasn't compatible with my previous gen foot controller on account of it's non-standard 100k pot. I kept using my 10k linear pot expression pedal for a few years with great results. But in pulling together my new foot controller design I decided to break it out of storage and get it working. What I wasn't expecting was that it's pot is logarithmic. The voltages hitting my A2D are definitely very flat towards the toe down position. The scaled CC goes from 0 to 100 very quickly and then basically crawls up to 127 over 75% of the travel.

What do other (DIY esp) foot controllers do with that? Convert the voltages back to a linear scale before sending a CC up to the Axefx? Or just pass it through unmolested by math?

I feel they should really be using linear pots. If you want to apply a log curve, do it in the wah block settings or something... not in the hardware.

 

[unix-guy]

The EV-2 has both Expression pedal jack and volume pedal jacks.

Use the expression jack for a controller as it's a linear pot.

The volume pedal jacks use an audio taper pot.

From the Fractal store:

The EV-2 is a compact EXPRESSION PEDAL, perfect for use with all Fractal Audio Systems products and many 3rd party devices. Unlike most expression pedals it has a true linear response with planetary gearing and a long, smooth pedal throw. The EV-2 doubles as an analog volume pedal, with separate IN and OUT jacks connected to an audio-taper pot. It features a sturdy cast metal housing, comfortable non-slip rubber tread. It is available only in black. In comparison to the EV-1, the EV-2 is smaller and lighter.

 

[fret]

Yes after some more investigation of this problem it seems the expression output of the pedal exhibits a linear response. However the voltage at my ADC is definitely NOT linear. So it appears there is a problem with the input circuit. It's a fairly simple affair. DPST socket with a 470K resistor on the "plugged" state which drops the voltage to 3.13 instead of 3.3, and a 150K on the power line (to avoid unpleasantness when the socket briefly shorts out during disconnection). IDK I'll have to ask some of the Raspberry PI / ElecEng geeks what I'm doing wrong.

Edit: Turns out I had the tip and ring around the wrong way. All sorted now.