Turn your guitar into a MIDI instrument, control keyboards or synth with the pluck of a string!

This unit is ‘monophonic’, meaning that only one note can be played at a time, but still very useful for solo playing. No modifications to the guitar are required as it makes use of the existing pickups. Here are a few tips for getting the best results out of the unit:

Always use a plectrum. This gives good stroke peaks for the software to read.

Make sure that only one string is making a sound, i.e. the one you want! Open ‘ringing’ strings, especially the lower pitch ones will cause frequency beating with the desired string. Muting strings with the palm of your hand, hemps to deaden the previous notes.

Do not pluck too hard, some high output pickups will overload the op-amp and cause the waveform to clip, this reducing the size of the peaks against the background harmonics. Keep an eye on the ‘peak’ LED and if it turns on a lot, reduce the guitar volume or pick softer.

It doesn’t take much practice to become good at producing reliable MIDI note data, and as a by-product it improved your picking technique.

Distributed with permission of Electron Publishing, as featured in October 2009 Practical Electronics Magazine:


  • MIDI Out DIN
  • 6.35mm (1/4”) Line In – Guitar In
  • 6.35mm (1/4”) Line Out – Guitar Thru
  • Peak LED
  • MIDI Note LED
  • Powered by 9v Battery
  • PIF16F88 Microcontroller
  • Measurements: 58mm x 93mm x 23mm

Build Instructions

IC1TL072 dual FET op amp1
IC2PIC16F88-I/P microcontroller, pre-programmed1
IC378L05 +5V 100mA voltage regulator1
LED15mm red light emitting diode1
LED25mm green light emitting diode1
C1, C3, C6, C7, C8100 nF ceramic Capacitor5
C2, C522 uF radial electrolytic, 35V Capacitor2
C44.7 uF radial electrolytic, 63V Capacitor1
R10, R11100 Ohm Resistor2
R12, R13220 Ohm Resistor2
R3, R44.7k Ohm Resistor2
R915k Ohm Resistor1
R718k Ohm Resistor1
R827k Ohm Resistor1
R1180k Ohm Resistor1
R5470k Ohm Resistor1
R2680k Ohm Resistor1
R61M Ohm Resistor1
IC1-118-pin DIL IC Socket1
IC2-18-pin DIL IC Socket1
SK35-way 180 type A DIN socket, PCB mounting1
SK1, SK26.5mm (1/4in.) PCB mounting stereo jack2
+V, GND9V Battery Clip1

Resistor Colours

x2 (R10, R11)
x2 (R12, R13)
x2 (R3, R4)
x1 (R9)
x1 (R7)
x1 (R8)
x1 (R1)
x1 (R5)
x1 (R2)
x1 (R6)

Board Layout

NOTE: Order of R2, R1, R3, R4 (not sequential R1-4)