Korg Forums

The Sp-280 supports half pedal on the damper and soft pedals, and according to the midi implementation chart it does this in 4 levels rather than continuous:
Damper
00(Hex) : Pedal Off
26(Hex) : Pedal Harf 1
4A(Hex) : Pedal Harf 2
7F(Hex) : Pedal On
Soft
00(Hex) : Pedal Off
5A(Hex) : Pedal Harf 1
6C(Hex) : Pedal Harf 2
7F(Hex) : Pedal On

The PU-2 pedal supports these functions, but I wonder if anyone can confirm if the pedal has potentiometers or switched resistors on these pedals?
It would also be good to know if potentiometers are used, does the internal sound generator receive continuous data even though only four levels are actually transmitted to midi out.
I'm also intrigued how 2 half pedals and a switch can be encoded into just 4 pins - ie common, switched sustenueto, and one pin each for soft and damper half pedals . So presumably resistance is being measured rather than a voltage measured from the wiper? Normally 3 pins are required for a single half pedal including the common.
Perhaps any Korg Techs browsing the forum can shed light on the above
Thanks!
Steve

I haven't seen the insides of one of thes pedal units but I think you're pretty much on the right lines with one common pin plus one pin for each pedal, be it a switch or a variable resistor. The piano that the pedal unit plugs into does the rest. For interpreting the resistance, the piano just needs another resistor, in series with the pedal pin and connected to a piano supply rail. A comparator, or several comparators is all that is needed, or an ADC.

There is another way which would only require two wires between pedals and keyboard, where the wires carry power and data, a bit like canbus works for vehicles.

It is possible to get a fairly good idea of what's in the pedal unit by using a multimeter on resistance range. Find the common pin, and then measure resistance between it and the other pins as the pedals are operated.
.

Thanks voip

Since posting I have acquired one of these pedals and so was able to make measurements. I can confirm that each pedal comprises 3 switches which close progressively as the pedal is depressed. I didn't open the unit but I assume resistors are switched in in parrallel. It's possible to see the switch unit in the gap under the pedals behind the springs.
These gives the four states for soft and damper , where one state is all switches open.