Doepfer MKE Universal Midi Keyboard Electronics Kit - Manual (Page 10)

MKE page 10 User's guide V2
potentiometers work as voltage dividers a wide range of resistance values for the
potentiometers can be used (~ 5k ... 100k, linear recommended).
The potentiometers connected to ST3, ST4, ST4 and ST6 (only for version 2)
generate these Midi messages:
ST3 generates pitch bend (with a small "plateau" around controller data 64)
ST4 generates modulation (control change #1)
ST5 generates volumen (control change #7)
ST6 generates after touch or any control change (only version 2)
For ST3 and ST4 the voltage range ~ 0 ... 1.6 Volt corresponds to the Midi data
range 0 ... 127. The reason for this limited voltage range is the rotating angle of the
wheels we offer as spare parts. An output voltage range of ~ 0...1.6V was measured
for these wheels if they are connected to GND and +5V as they do not cover the
complete rotating angle because of the end stoppers.
For ST5 and ST6 (only version 2) the full voltage range 0 ... 5 Volt corresponds to the
Midi data range 0 ... 127 as normally standard rotary or fader potentiometers are
used for volume control.
In version 1 of MKE ST6 is a pin header with 4 pins (compatible to the 4 pin after
touch connectors of the Fatar keyboards):
• left (pin# 1) measured voltage (after touch connection)
• (pin# 2) +5V
• (pin# 3) measured voltage (after touch connection)
• right (pin# 4) +5V
The pins 1-3 and 2-4 are shortened. The pins 1+3 correspond to the potentiometer
wiper terminals of ST3/4/5 and are connected to GND on the MKE board with a 10k
pull down resistor. The Fatar after touch sensors function as variable resistors. The
resistance decreases if pressure applied to the sensor. The sensors forms a voltage
divider with the 10k pull down resistor. Consequently the measured voltage is ~ 0V if
no pressure is applied and increases as more pressure applied to the sensor. For
some keyboards the 10k pull down resistor (R12) has to be changed for the best
result (down to 100 Ohm for some types). The easiest solution is to solder a second
resistor in parallel to R12 until the best result is obtained by trial and error. The after
touch sensors of the Fatar keyboards are not very sensitive and it might be a problem
to dose the Midi after touch as desired. But this is not a problem of the MKE but of
the after touch sensors.
Instead of this a sustain pedal (resp. a jack socket to connect the sustain pedal) can
be connected between pin 1 and 2 of ST6: as long as the sustain contact is open the
measured voltage is 0V (
→ → → → Midi data = 0) because the pull down resistor R12 is
effective. As soon as the contact closes the voltage jumps to +5V ( → → → → Midi data 127).
For this type of connection a sustain pedal with contact open at rest has to be used.
If a sustain pedal with contacts closed at rest is used (e.g. VFP1 or VFP2) ST6 resp.
the jack socket has to be wired in a different way and a small modification of the MKE
circuit is necessary: the 10k pull down resistor R12 has to be removed (above
ST4/ST5). Instead of this the 10 resistor is connected between pin 1 and 2 of ST6 (on
the pcb bottom side, not at the pins of ST6). Now it is turned into a pull up resistor
that pulls the measured voltage to +5V (
→ → → → Midi data 127). The sustain contact resp.
the jack socket is connected between GND and pin 1 of ST6. GND is e.g. available at
one pin of ST3/4/5. Now the measured voltage becomes 0V (
→ → → → Midi data = 0) as the
sustain pedal contact is closed at rest. As soon as the sustain pedal is operated the
pull up resistor becomes effective and Midi data 127 is generated.