Pianet Robot

Research project on the development of new tools for musical expressionnt


an automated Hohner Pianet-T

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 coils 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: This circuit being identical to the one used for earlier robots such as <RorO>, <Pos>, <Per>, <HarmO>, <Qt>... we do not give any comments here but ask the interested reader to consult the web-pages dedicated to these older projects.

Here is an overview over the circuitry: The solenoids used here have an external return spring compensating for the weigth of the anchor at rest. At the push side we gave them the 'fingers' we designed long ago for our player piano. Here is a picture of the prepared solenoids before mounting on the chassis: The solenoids are rated for 12V operation

The midi implementation was worked out such as to make this robot compatible with existing midi files for our player piano. Hence the use of midi channel 0. The note repetition mechanism also is compatible with our player piano. However, the mechanics of this instrument being fundamentally different than those of a piano, one cannot expect the velocity scaling to be compatible with that of the piano. Of course we dropped all support for a pedal, as this instrument does not have one. Technically speaking it would even be impossible to provide a pedal in this case.

Source code and hexdumps for the PIC microcontrollers:

board processor source code hex-dump PCB file
Hub/parser 18F2620 Pianet_Hub.bas Pianet_hub.hex PCB_Pianet_Hub.gif
Board1 18F4620 Pianet_PH.bas Pianet_PH1.hex PCB_12PH.gif
Board2 18F4620 id. Pianet_PH2.hex id.
Board3 18F4620 id. Pianet_PH3.hex id.
Board4 18F4620 id. Pianet_PH4.hex id
Board5 18F4620 id. Pianet_PH5.hex id.

In 2024 we decided to add internal amplification and speakers to this robot such that it could become a stand-alone robot not requiring any external equipment. This lead to the addition of two new controllers in the midi implementation: controller #7, for volume and controller #10 for panning, in this case steering the amplitude relationship between the front and back Altec dome speaker. The design of the PWM-controlled volume makes use of two fast Silonex vactrols. This is the circuitry used:


Midi Mapping and implementation:

Note-off, no release

Note-on, velocity implemented

Key pressure: used for automatic note repeats. Each note can be programmed with an individual repetition rate. Key pressure can also be used to modify light flashing speed.


Controllers implemented:

#6: Leslie tremolospeed: amplitude modulation of alternating front and back speakers. This mechanism overrides the panningcontroller #10. Default setting: OFF.

#7: With the internal the audio system connected, this controller can be used to steer global volume of the amplifiers. By default this controller is 0, so sending it prior to playing is a requirement.

#10: This controller steers the 'panning' between the front and the back speaker. By default this controller is set to 64.

#30: Global repetition rate controller. Value 0 disables repetitions. Note that repetitions will we synchronous and in sync only if the notes to which they are applied start at the same time. By default set to OFF.

#66: Power on/off switch. This resets controllers and switches the power supplies for the solenoids. Value 0 switches OFF, any other value is ON. Switching this controller also resets all controllers to their default values on cold boot.

#69: Switches automation of the lights on or off. Values 1 to 7 select different light mappings. Value 0 switches the mechanism off. By default, automation is switched ON.

#123: All notes OFF. (Includes the lights).

Program change: not implemented

Channel aftertouch: not implemented

Pitch Bend: not implemented

Technical specifications:

Design and construction: dr.Godfried-Willem Raes

Collaborators on the construction of this robot:

Music composed for <Pianet>:

none specific sofar. However, <pianet> is often used for concerts at venues that do not have a piano available. It also can replace the spinet in quite a few orchestrations.

Pictures taken during the construction in our workshop:



Back to composers guide to the M&M robot orchestra.

Back to Main Logos page:index.html To Godfried-Willem Raes personal home page... To Instrument catalogue Go to Godfried-Willem Raes' homepage



Dit automatiseringsprojekt ging van start op vraag van Alain Van Zeveren. Het maakte oorspronkelijk dan ook geen deel uit van ons grote projekt rond de bouw en ontwikkeling van het robotorkest bij Stichting Logos. De belangrijkste reden waarom voor dit projekt geen plaats was 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 was nu eenmaal een paradigma achter het Logos robotorkest.

Niettemin, omdat na de automatisering van het Hohner pianet, het projekt wat verweesd in onze werkplaats was achtergebleven, beslisten we het toch tot een autonome robot uit te bouwen en af te werken. Dus ontwierpen we een deugdelijk wielstel met kruisdisselbesturing evenals een versterkersystreem uitgerust met twee antieke University Sound -de voorloper van JBL-Altec- speakers. De <Pianet> robot kan nu worden ingezet op plaatsen waar een beroep gedaan wordt op het robotorkest maar waar geen vleugelpiano aanwezig is. Ook als vervanger voor het spinet, is het erg geschikt.


Bouwdagboek - Construction & Research Diary:

(Terug) naar logos-projekten:


Terug naar Logos' index-pagina:


Naar Godfried-Willem Raes personal homepage... Naar katalogus instrumenten

gebouwd door

Godfried-Willem Raes

Go to Godfried-Willem Raes' homepage M&M orkest

Last update: 2024-02-21 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:

Fuse in the power entry: 4 A. A spare fuse can be found in the little drawer.

Wiring & circuit details midihub board:

By changing the jumper on this board it is possible to select between parsed midi mode (1 ms delay) and direct mode. Direct mode may lead to much higher jitter on the timing precision, depending on overall midi density. The protection diodes (1N4007) for inductive loads have been ommitted in the practical realisation as the mosfets are only used to switch lights here.

PCB for this 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

All boards use IRL640 for the holds.

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
FQPF20N06E 60V 15A 3V    

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

Solenoids: Intertec ITS-LZ-1949-D-12V. Datasheet. Nominal voltage: 12V , Power: 7W (Hence Rdc= 20.57 Ohm). With the 9V hold-voltage only, the current drawn is 437 mA. During the velo-pulse, current rises to 1.6 A.

Audio amplifier circuit:


Mechanical construction drawings and welding plan:

Tentative cost calculation:

tubular solenoids:
PCB's P/H boards:
Hub board
Power supply: 9V - 11A
Power supplies 24V - 6A / 9A
Chassis Vorsetzer
Konnektors 2p Weidmueller
Ettinger M3 shock absorbers
Rubber fingers
Metal plated wood
M6 bakeliet knoppen
Material cost estimate

Labor (estimated at 4 weeks): 6.300,-

Total estimated cost: 10.100,- [16.12.2021]

Additional costs for the construction of the trolley and the amplifier system:


Total estimated end cost: 16.100,- Euro.


Raes, Godfried-Willem, "Expression control in musical automates", 1977/2024,