< Vibi >

an automated vibraphone

Godfried-Willem RAES

2001 / 2005 / 2010

Technical Description

Our own design had to become a computer controlled acoustic vibraphone with touch control and individual dampers for each single bar. The starting point for the practical construction was an small model Yamaha vibraphone (type YV-600B, serial number 1977) ) of which we only kept the tuned aluminium staves and the resonators. The original global damping mechanism (activated by the pedal) was thrown out altogether. A new electric circuit was designed for the vibrato mechanism, since the original one was too noisy and could not be easily computer controlled. As an extra bonus -not found on any commercially existing vibraphone- we wanted the flap valves for the resonator tubes implemented not only as a rotating vibrato mechanism, but also as a volume control. This entailed precise control of the position of these valves as well as a return to a determined position after a period of normal rotation.

The beaters make use of Lukas Ledex solenoids (similar as the ones we used for our player pianos), mounted under the extremities of the sound bars. The dampers were made with the same type of solenoids, but here we mounted rubber or felt pads on the anchors as dampers. No springs were used. The anchors falling back on a heavy felt covered steel bar by gravity alone. The design started off with an analysis of pulse timing requirements for the automated vibraphone:

The attack pulse tv1.tv2... (for power supply voltage of 44V -see further) should range between 3ms and 15ms. If we want good dynamic controll, it is enough to controll precisely the pulse width of the attack solenoids with the beaters. The pulse duration for the dampers (td) could be constant and, if so, equal to the minimum pulsewidth required to damp the bar (ca. 50ms) . At rest, the damper can be released, so no power is spoiled. The maximum repetition speed will be dependent on the dynamic used and is limited anyhow by the time required for the beater to fall back plus the time for the damper and the time for this damper to fall back. Of course, when playing very fast repeated notes one could decide not to use the dampers. But even than, the repetition rate will be determined by the time it takes the beater to fall back. If we mount the anchors with springs, the fall back time can be decreased, but only at the detriment of dynamic range: the heigth of the (compressed) spring should be subtracted from the original movement traject. Also springs unavoidably introduce their own resonant frequency, interfering with some specific repetition rates.

This design offers many more musical perspectives than either what musician playing vibes could have to offer. First, it is truly polyphonic with complete autonomy for the individual beaters. So no longer a limitation to 2 ,4 or if conservatory acrobatics are used, 6 notes/sticks. Second, as we provided individual dampers for each bar, the musical possibilities in terms of expressive refinement are greatly enhanced. Third, since we finally decided to also implement velocity for the dampers, we can control the damping up to the smallest detail. This way even the most 'avant-garde' playing techniques can be realized on this automate. What we have not implemented is changes of sticks, as musicians are often required to do in typical contemporary music pieces. This would have required at least yet another row of solenoids with softer beaters. There is barely enough space under the bars to allow for such an untertaking. Of course we could place them above the bars, but then one potential element of magic in the instrument would disappear: the possibility of manualy playing the instrument at the same time as its automate plays. Nevertheless it requires the user only to exchange all 37 beatercaps if it is realy required to sound this vibraphone with a softer (or harder) attack.

A new element in the design of this robotic instrument is that we implemented a damper-hold mode, whereby the felt covered dampers can be pushed against the staves with a continuously variable force. Thus the staves can also be played whilst damped to a variable degree. It was easy to implement this since 8254 type timer chips can be programmed to operate either as programmable one-shots or as square wave generators. In the latter case, since their outputs drive the solenoids via mosfets, we take profit of the fact that the coils impedance rises with the frequency of the applied voltage. Thus the current through the solenoids can be controlled by programming the periodic frequency of the timer chips. At some operating frequencies in the audio band however, this operational mode can lead to audible noise stemming from the solenoid anchors. This possibility however is only available when controlling <Vibi> with a laptop of its own. The midi-input version has no support for this operational mode.

As usual in our instrument designs, we constructed TIG welded steel frames for the entire magnet and electromechanics assembly. Bolts on the sides of the instrument in combination with the bolts holding the fallback bars under the solenoids, allow for fine adjustment of the traject of movement for the beater and the dampers. This affects the dynamic range. The instrument was mounted on large and very sturdy wheels of the same type as used in most of our other robots that make up the Logos <M&M> robot orchestra.

The note range of the instrument is 37 notes, 60 to 96(C-c") expressed in midi notes.

For the electronic control of this instrument we used hardware we originally designed for player pianos. Originally the instrument was played using a Wintel Pentium PC. The demultiplexer for the parallel input is a left over from this original design although now it is controlled by a PIC microcontroller taking input from MIDI data directly. The demultiplexer looks like:

The note driver board and the velocity controll circuitry was build after following schematics, using intel 82C54 programmable timer chips, used as programmable one shots in this application. The pulse width, using a 1MHz clock, is programmable between 1 microsecond and 64ms. The practical (and musically relevant) range used and set in the software is 3.5ms to 16 ms. We use the following formula for the rescaling of midi velo values into microseconds: pulse = 2048 + (velo * 128/4) + (velo^2 / 4). This was implemented in the PIC firmware. The dampers use a different mapping.

bus-demultiplexer PC board lay out

8254 velo board lay out

(These PC boards -without components- could be obtained against cost from the author for a few years. Now the design is replaced by a newer one, but occasionally you may encounter one of these boards as we sold quite a few of them). One board accomodates one octave. .

The solenoids used are: Ledex STA series push tubular solenoid type nr. 195207-228. They have a cold DC resistance of 19.1 Ohm. The nominal working voltage, at which the coils can be activated indefinitly long is 13.8V. At 10% duty cycle, a voltage of 44V may be applied.

motor board:

The resonators, as usual on a vibraphone, have a rotating mechanism allowing them to be periodically opened and closed. Each row of resonators has its own rotating shaft. So we provided 2 stepping motors, such that rotational speed of upper row and lower row can be controlled independently over a wide range. To achieve this, up to 2010, we used the two 8-bit auxiliary ports on our demultiplexer board to controll two PIC microcontrollers. Thus the software could suffice by sending a byte (0-255) to control the rotation speed of the motors. The original code, microcontroller basic, for the PIC's can be found in our Stamp directory. In 2010 however, we improved the mechanism quite a bit. The first problem with the original implementation was that whenever the motors were stopped, the end position of the shutters was unknown and arbitrary. Proximity sensors, such as used in our design for <Korn>, thus were added in the new design. Now the motor can be stopped in a predetermined and programmable position. Also, we were not fully satisfied with the range of the speed control. To improve this -keeping the same motors- we decided to go for a full bipolar drive using a small Nanotech motor controller. This increased the torque considerably on high speeds. The new circuit looks like:

 

An overview of the final assembly of all circuit boards used for <Vibi>, looks like:

The power supplies, modified in 2010, now look like:

The wiring of the PIC-board translating midi-input to our parallel bus looks like:

[comments on these circuits, first developed for one of our player pianos can be found at/kursus/2116.html.]


<Vibi> has played at following venues/occasions: Tourcoing (France, Le Grand Mix), Ghent (Logos Tetrahedron), Amsterdam (Paradiso), Herne (Germany, Teutoburgia Halle), KULAK University (Kortrijk), Yttre (Wallonia), TART symposium (Enschede), Festival in de Branding (Den Haag), Adventures Festival (Korzo Theater, Den Haag), Lille 2004 (Aeroneff, Lille), Muenchen 2005, DeAvantgarde Festival (Muenchen), November Music (Den Bosch), Computed Music IV (Koeln), Jauna Muzika Festival (Vilnius, 2007), Orgelpark (Amsterdam, 2008), Dag van de Oude Muziek (Alden Biesen, 2010), STAM-opening (Ghent, 2010)...

Available repertoire for <Vibi>, alone or in combination with other automats.


Tech-Specs -----------------------------------------------Technische specifikaties:

Aanvang bouw: augustus 2001 - . <Vibi> speelde zijn eerste toonladder op 9 oktober 2001 en was volledig afgewerkt op 16 oktober 2001. Het materiaal van de aanslagkapjes werd vernieuwd in 2004. In 2005 werd <Vibi> omgebouwd zodat hij ook zonder laptop besturingskomputer rechtstreeks midi signalen kan verwerken. Het vibrato mechanisme werd helemaal herzien in 2010.

Size-----------------------------------------------------------------------------------------------------------Afmetingen van het afgewerkte instrument:

  • diepte: 700mm
  • breedte 1450mm
  • hoogte 800mm (+ stuurstang, uitstekend boven klankstaven, maar demonteerbaar)
  • Gewicht: ca. 95kg

Power--------------------------------------------------------------------------------------------------------Stroomvoorziening:

  • 230V / 2.5A - 50/60Hz

Insurance value (for organisors):

16.000 Euro

Rental / concerts:

This instrument can be rented from Logos Foundation. A technician from logos will allways accompany the automat. The tarif is 500 Euro a day. We have quite some repertoire for the instrument alone, or in combination with other automats. On request, pieces can be programmed/adapted to be played on this automat. Feel free to inquire for conditions. Transportation is possible with a normal liftback car if it is capable of holding an ordinary table. A small van will always do. A ramp is required to lift the instrument in the car. However, the instrument cannot be taken apart.

 

Midi Implementation

Midi Implementatie:

The default midi channel for <Vibi> is set to 10 (if counting channels from 0, otherwize its 11)

  • Note ON (&H90) notes 60 to 96 with attack velocity byte.(144+channel, note, velo).
  • Note OFF (&H80) : notes 60 to 96 with release velocity byte (128+channel, note,release_value) . This works only if the functionallity is enabled by the corresponding controller: 23, set to 1 and sustain is OFF.
  • Volume controller: 176 + channel, 7, value: position of the resonator valves. With value 127 they will be fully opened, with 0, closed. Obviously, the use of this controller contradicts the use of the vibrato mechanism and this should only be used with controller 22 set to OFF.
  • Vibrato controller: 176 + channel,20, value (This controlls the speed of the diatonic motor for the vibrato mechanism) Speed range is 1:10.
  • Vibrato controller: 176 + channel,21,value (controlls the speed of the chromatic vibrato motor)
  • Vibratocontroller: 176+channel,22,value (This controlls both motors together)
  • Damping controller: 176+channel,23,value (This controlls the force wherewith the dampers strike the bars on reception of a note off command, if damping mode is set to 0. If damping mode is set to 1, this has no effect as the damping forces will be controlled by the release value passed with the note-off command). Also, when sustain is on, this controller will have no effect.
  • Damping mode: 176+channel, 24, 0 = use the release value sent together with the note off commands. 1 = use the value set with the damping controller to damp the notes after reception of a note off. This switch has no effect if sustain is ON. [new]
  • Sustain switch: 176+channel,64,value (0 means no sustain, so the dampers will be active when a note off is received, 1 means no damping will occur).
  • Start-Up command: 176+channel, 66, 1. Activates the solenoids power and realligns the vibrators to the fully opened condition.
  • All notes off: 176+channel, 123, 0: resets all solenoids and resets all controllers to the default startup values. Also dims the lights and stops the motors.
  • Lights: Mapped on the notes 120 to 123. The velocity byte steers the light strength. Note pressure can be applied to set a flashing speed if required. Note off commands switch off the light and stop the flashing. The all notes off controller will also switch off all lights.
    • note 120: Red LED spots on the circuitry on the backside (in parallel with 4 large but soft red LED's)
    • note 121: Bright white front lights (LED assembly inside steel beam carrier above wheel) (3 x 3W LumiLeds)
    • note 122: Yellow LED strip on the front side behind the resonators.
    • note 123: Bright white LED assembly on the low side of the automate inside the steel beam carrier. (3 x 3W LumiLeds)
Some extra controllers are implemented in <Vibi>'s firmware for debug and allignment purposes. These should never be send by users. These reserved controllers are: 32 (accelleration slope for the motors), 70 (callibration command), 71 (diatonic sensor offset allignment adjust, default value is 37), 127 (With value 0, forces a reboot of the solenoid microcontroller in Vibi. If the midi receive channel is changed using the DIP switches, this controller should be send to cause a reread of the channel. After this code is received, you should wait at least 5 seconds before sending new commands over midi. This feature was added for debug and development and should not be used normally.)

 


Repertoire:

Godfried-Willem Raes <A Last Repetitive>, 1976 for naked dancer and vibraphone
Godfried-Willem Raes <Vibes for Vibi>, 2001

solo composition - environmental music, with optional <Harma> and <Piperola> part. (Premiered on the Polymachina festival, Tourcoing, 2001)

Available on CD: LPD008

  <Trio Paradiso> for <Vibi>,<Klung> and <Harma> (Commisioned by Paul Koek, premiered at Paradiso Amsterdam, 12.11.2001) [5'00"]
  <Paradiso>

for <Vibi>,<Klung>,<Player Piano>,<Harma>,<Piperola> and optional musicians [10'30""]

Available on CD: LPD008

  <Eary Lis Trimbl>

for automat orchestra, a naked singer and optional musicians [10-15'], 2002

Available on CD: LPD008

  <Lithos> for complete automat orchestra, including <Vibi>. Act1 of Technofaustus.
  <GeroVibi> for invisible instrument and a naked player
  <Tekne> for complete automat orchestra, including <Vibi>, from Technofaustus (mefistodance)
Eric Satie Ogives  
Howard Skempton <Pendulum>  
John Cage    
Barbara Buchoviec <Moonflower> for vibi solo LPD012
Kristof Lauwers <Generic Sonatas>

for automat orchestra, 2002

Available on CD: LPD008

Sebastian Bradt

<And they...>

for automat orchestra
  <Zurge> for automat orchestra
  <Everything> for automat orchestra
Kristof Lauwers <Plastic Deformations> for automat orchestra (percussion robots only). Available on CD: LPD014
Xavier Verhelst <SillyVester> for automat orchestra
Sebastian Bradt "Treefingers" for vibi, harma, piperola, bourdonola. Available on CD: LPD013
Godfried-Willem Raes "SQE v STO 4 QR" for percussion robots. Available on CD; LPD014 (Robodies)
Godfried-Willem Raes "Icy Vibes" for Vibi for Namuda dance, viola, vibi, QT, Bomi, Harma. Interactive version of 'Vibes for Vibi'.

 


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Construction assistants for <Vibi>:

Service manual & detailed circuit and maintenance documentation

Following information and documentation is not intended for the general public. It is provided as technical documentation for our maintenance staff at Logos Foundation.

Setting <Vibi> up:

Switching <Vibi> on:

When the power is switched on, the 5V (all logic circuits and PIC controllers), the 26V (stepping motors) and the 12V (relay and lights) power supply will start. Then one of the microcontrollers on the motor board will wait for the reception of a controller 66 ON command and only if this match is found, the 48V power supply will be switched on. The PIC controller switches a relay on, causing the AC supply to the 48V SMPS to switch on. To switch solenoid power off, controller 66 with value 0 should be send.. So, remember to always first switch on <Vibi>, and than start the PC's application. Other functions such as motors and lights will work even when controller 66 was not received.

Circuit boards overview:

There are four power supply systems: the first one creates the 5V logic supply, the second one only the 44V for the solenoids, the third the +12V for the relay and the lites and the fourth one, the +26V for the motors.

All solenoids have a common positive voltage connection, connected to the +48V power supply. This power supply is mounted on the back side of the circuit boards assembly, where also the demultiplexer board and the stepping motor boards can be located. The second wires come together in Weidmueller 4-pole connectors (three for each board covering an octave) to the note hold and velo boards. The positive voltage can be adjusted on this power supply printed circuit board with the multiturn trimmer. The voltage should be adjusted such that when the shortest velocity pulses are applied, the solenoids develop just enough force to barely hit the bars. Initially we found 44V to be a suitable setting. This is the highest voltage allowed for a duty cycle of 10%. When testing software, it is best to temporarily use a lower voltage (say 24V) power supply to avoid burning out the coils due to software errors and code bugs.

There are 8 timer boards (each covering an octave) on the mounting plate. The last board on the bus (the note board for notes 0-11), has Shottky termination diodes (BAT45) mounted between ground and +5 over the data lines as well as over the A0,A1 adress lines for the timers.

Although the midi mapping is on notes 60-97, the hardware as well as the corresponding low level driver code in the PIC remaps this into 'hardwire' notes 0 to 37 (for the beaters) and 48-85 (for the dampers). The beaters use the strobe signals generated by the first velo 74154 demultiplexer, whereas the dampers use the second chip. The third chip on the demultiplexer board is not used in this application. All strobe signals are negative pulses, minimum 1 µs, maximum about 12 µs in length. Thus the use of long interconnecting cables is possible (although, not advisible).

Alligment of the sensors: After startup and the automatic calibration routine, the blue LED's on the motor control board should flash everytime the sensor anchor passes the sensor. If this is not the case, the anchors need adjustment. Note that the anchor on the diatonic side has a slight offset, due to the excentric placement of the holding bolt on the turning wheel. Further, if the blue LED's do not flash periodically on rotary movements, the functionality of the CC7 implementation will fail. Also it is possible that the motor continues spinning if for one reason or another the sensors do not give out the expected pulses. The voltage on the AD0 input of the PIC when the anchors are away from the sensor is 1.75 V, with the anchor in the most extreme proximity of the sensor, it is 4.39 V. (measured on the chromatic sensor). The resolution of the AD convertor is 10 bits.

Maintenance logbook:

2001: First working version finished. Controlled by a Sony Vaio laptop computer using a National Instruments NiDAQ DIO-24 PCMCIA card. Any centronics compatible output port can be used.
15.01.2005: Input circuit modified such that Vibi now takes midi commands directly, using a PIC controller.
28.06.2005: 5V/12V SMPS removed and replaced with 2 analog power supplies. Midi in series resistor (was 220 Ohms) reduced to 133 Ohm by parallelling the existing value with an 330 Ohm resistor. This improved the quality of the midi signals considerably. Optocoupler is 4N27, mounted on the PIC board.
01.07.2005: White LED spotlights added on backside. 4 large red LED's as well. Documentation updated.
25.04.2007: Vibi damaged after transport to Vilnius. Repaired locally: note board 60-71, 5V power supply connector broken off because resonator tubes jumping out of their holders in transportation. Vibi returned from Vilnius on may 2nd.
10.01.2009: The modulation wheel motors need a replacement...
13.10.2009: Belt for diatonic vibrato motor replaced.
10.05.2010: Note 82, damper solenoid burned out and mosfet gone... repair required.
10.06.2010: All beater caps replaced with new ones.
09-10.10.2010: Vibi plays on the opening of the STAM museum on the Bijloke campus: 12700 visitors...
10.11.2010: Start of a redesign of the motor mechanism, associated electronics and firmware. We want to add sensors to the tremolo mechanism such that we can stop the motor in a position with the resonators fully opened.
13.11.2010: Construction and mounting of a Pepperl+Fuchs position sensor for the chromatic resonator motor mechanism. The diatonic side was more of a problem due to the severe space constraints. Here we mounted the sensor anchor on the holding bolt of the drive wheel. A small offset to the full opened position thus became unavoidable and had to be remedied in the PIC firmware. With the new hardware, it will be possible to add lights to <Vibi>. The placement of the sensors can be seen in the pictures. The sensors are mounted with M2.5 bolts and nuts.
14.11.2010: Physical design... trying to make space for the new hardware...
19.11.2010: New pic controller board breadboarded. Two controllers, 18F2520 are used.
20.11.2010: Yellow LED strip mounted behind the frontal resonators. Two Nanotech motor controllers mounted. Breadboard circuit with two PIC microcontrollers finalized. Start coding for the firmware. Vibi webpage edited according to the new implementation and hardware. Old version saved as Vibi_2005.html.
21.11.2010: Wiring of all new hardware on the Vibi carrier plate. Further coding on the firmware using MPLAB and the Proton+ compiler. There are two source code versions, one Vibi_MotKro.asm and the other Vibi_MotDia.asm, since both PIC's listen to different controllers.
23.11.2010: Firmware source code changed such that we can use a single source code file for both PIC's: Vibi_Motors.asm, making use of metacompiler commands.
24.11.2010: Version 1.0 flashed and tested. Some minor bugs need to be killed. The control range for the motor speed in a substantial improvement over the previous version. The positioning code seems to work pretty well as well. We have to improve the firmware such as to take into account the small offset caused by the eccentric placement of the sensor on the diatonic note row.
25.11.2010: Test and evaluation session for the new firmware. White light (note 123) added, using three 3 W Lumileds. Existing lights made controllable.Version 1.1 firmware flashed: with offset compensation for the diatonic sensor. Frontlite still to be mounted. For debug and fine tuning purposes, we implemented controller 32 (accelleration slope), controller 70 (callibrate command) and controller 71: offset value for the diatonic sensor. The controllers should not be used by users.
26.11.2010: Front light mounted: again three 3W LumiLeds. Further firmware debug on controller 7 implementation. Version 1.2 now.
27.11.2010: Firmware version 1.5, motor speed much increased now. The accelleration code in the firmware is crucial now since the motor will not start up on high speeds otherwize.
28.11.2010: Test code added in GMT for development controllers 71, 72, 32, 70. Firmware version 1.6 flashed in both PIC's. Highest (fake) resonator tube sawn away for better access to the microcontrollers. Actually, all resonator tubes can be shortened quite a bit as most of their length is non-functional, a disgusting feature of all vibraphones is seems... PIC code seems to work nicely now, but calibration every so often may be required for reliable positioning with controller 7. Making the valves rotate will always readjust the motor position as position is reset everytime the valves pass the sensors. Awaiting feedback from users now... Repair of one of the damper solenoids still to be done.
29.11.2010: Firmware improved to take into account the death traject wherein the sensor is triggered. Now version 2.0.
02.12..2010: Backside lights replaced with 2 x 3W red LED spotlites

17.04.2013: Two metal strips added to prevent the resonators from jumping out during transportation.
20.04.2013: <Vibi> survived the trip to Glasgow very well! We expect it back in Ghent on monday 22nd of april.
23.04.2013: Vibi returned in perfect shape from Glasgow.

05.09.2013: Problems when attempting to send RS485 midi to Vibi's input port. Similar problem as occured with <Piperola>. Replacement of the 4N27 or CNY27 optocoupler with a 6N317 was the cure. The input port is now compatible with standard midi and differential RS485.

 

 

Last update: 2013-09-05 by Godfried-Willem Raes