Line Frequency
The Voice of Protons
MCP3201 ADC -> RPI
Proton-Mag I
Proton-Mag II
UV PCB Writer
Lab Power Supply
Light Barrier
Strange Sensor
Solar Controller Hack
Pedal with 270℃ Poti
Misc Stuff
About Myself


I'm sorry, but the translation of this page is still not completed. However, you may try to view the German version first by clicking on the little German flag sign.

Here just a quick summary and the pictures. It's about using a standard 270 degree potentiometer in a musical keyboard foot expression pedal that usually needs a 45 degree type of potentiometer. The trick is to use a low-power, rail-to-rail OpAmp to compensate the small movement angle.

The original pedal:

[Bespeco Volume Pedal]

The reference, the Roland EV-5:

[Roland EV-5]

How it looks on the synth side (newer use 3.3V):

[Roland U-20]

The compensation circuit consumes only about 300uA, not more than the EV-5 10k potentiomenter:

[Schaltung zur Drehwinkelkompensation]

Prototype, here without protecting diodes:

[Platine zur Drehwinkelkompensation]
2023 Alexander Mumm