Pianet Robot

Research project on the development of new tools for musical expressionnt



an automated Hohner Pianet

dr.Godfried-Willem RAES


[Nederlandse versie]


An automated Hohner 'Pianet'. This instrument is a five octave keyboard instrument using tuned steel blade springs, clamped at one end, as tone generators. At rest, a rubber damper rests on the springs. This rubber damper is released as soon as a key is depressed. The attack of the sound can be influenced by the speed and force wherewith the key is depressed. So it is touch sensitive to a certain extend. However, due to the electromagnetic pick-ups (small solenoids wound on a permanent magnetic core all connected in series) , the sound is quite one-dimensional and in that respect similar to the electric guitar. On this picture the mechanism can clearly be seen: The electromagnets (transducers) and their series connection are clear on this picture: The circuit used to implement velocity sensitivity came out like this:


Midi Mapping and implementation:

Note-off, no release

Note-on, velocity implemented

Key pressure: used for automatic note repeats

No controllers implemented


Technical specifications:

Design and construction: dr.Godfried-Willem Raes

Collaborators on the construction of this robot:

Music composed for <Pianet>:


Pictures taken during the construction in our workshop:



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Dit automatiseringsprojekt ging van start op vraag van Alain Zeveren. Het maakt dan ook geen deel uit van ons grote projekt rond de bouw en ontwikkeling van het robotorkest. De belangrijkste reden waarom voor dit projekt geen plaats is binnen het robotorkest, heeft te maken met het werkingsprincipe van dit instrument dat, hoewel het geluid veroorzaakt wordt door vrij trillende stalen tongen, immers onmogelijk kan klinken zonder toepassing van een externe versterker en dito luidspreker. De afwezigheid van luidsprekers voor versterking is nu eenmaal een paradigma achter het robotorkest.


Bouwdagboek - Construction & Research Diary:

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Godfried-Willem Raes

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Last update: 2021-12-05 by Godfried-Willem Raes

The following information is not intended for the general public nor for composers wanting to make use of the <Pianet> robot, but is essential for maintenance and servicing of the robot by our clients and collaborators. It also might be usefull for people that want to undertake similar projects.

Technical drawings, specs and data sheets:

Power supplies:

Wiring & circuit details midihub board:

Circuit details solenoid driver board:

board 1 using 12 IRF620 MOSFET's for the pulses

board 2 using 10 IRF530 MOSFET's for the pulses, 1 IRF540, 1 IRF1310

boards 3 to 5 using 12 IRF3710 for the pulses

summary of data-sheet values for MOSFET's used:

type Umax Imax Ug RdsON Ci
IRF530 100V 14A 10V 0.18 Ohm  
IRF540 100V 28A 10V 0.08 Ohm 1.7nF
IRF620 200V 5A 10V 0.8 Ohm  
IRF1310 100V 24A 10V 0.036 Ohm 1.9nF
IRL640 200V 18A 5V 0.18 Ohm 1.7nF
IRLZ34 55V 30A 5V 0.046 Ohm 880pF

If repair and replacement is required, all N-channel mosfet's can be replaced with IRL640 types.


Mechanical construction drawings and welding plan:

Tentative cost calculation:

tubular solenoids: 60 13.50,- 810,-
PCB's P/H boards: 5 250,- 1.250,-
Hub board 1 200,- 200,-
Power supplies   350,- 350,-
Chassis   200,- 200,-
Material cost estimate     2.810,-

Labor (estimated at 3 weeks): 4.725,-

Total estimated cost: 7.535,-


Raes, Godfried-Willem, "Expression control in musical automates", 1977/2021,