<Pos>


an automated organ positiv

Godfried-Willem RAES

2018

[Nederlandstalige versie]

Robot: 'Pos'

In december 2017, out of the blue, we received an email from brother Kris Oelbrandt in a Dutch Benedictin monastery offering us a small pipe organ for free. Of course we could not turn this down and on january 2018 we transported the instrument to our instrument building workshop at Logos Foundation. The organ was made by Gerard Pels in the early nineties of the 20th century, an outstanding organ builder based in Herselt. He was born in 1955 and died in 2014. In 2017, the Pels organ factory itself went bankrupt and stopped activity. The original design and order was for a tuning system using 13 notes per octave based on just intonation intervals, an idea worked out by composer Kris Oelbrandt. Here is a link to the document describing this tuning system. When he entered the monastery in 2002, the organ found a use in the religious rituals at the monastery in Zundert and to serve that purpose it was modified and retuned by Gerard Pels to conform to 12-tone equal temperament. This is the organ as it arrived in our workshop: The sizes were: depth: 335 mm, width: 1223 mm and height (including the pipes): 2210 mm. (sizes not including the keyboard, a separate component).

The single register (8' holpijp) was realised as follows: The lowest octave (note 36 to 48) are stopped wood pipes placed on the back row on the wind chest, the mid register (notes 49 to 93) are stopped tin pipes with an inverted resonator tube mounted on the inside of the pipe stops, and the highest 7 notes (94 to 100) are open tin pipes. The pipes are arranged in three rows. In the windchest, solenoid driven valves are used, thus highly simplifying the automation of the instrument by us. The keyboard was a regular 5-octave organ keyboard with electric contacts connected to the organ through a single multiconductor cable. Here are some detailed pictures: Here is a drawing of the construction of the metal pipes, showing the internal resonator tube (inside soldered chimneys, in the proper language of organ builders):

Unfortunately for us, the multicable used no color coded wires but plain enameled copper wire... We could figure out the wiring from measuring and testing on the connector used to connect organ and keyboard: The original wiring had a common ground connection and diodes across the pallet valve solenoids. It was wired as drawn here: All diodes needed to be removed and replaced with VDR's to make automation easy. High side mosfet switches are a lot more troublesome to design than the usual low side switches. This is what the palet lifting solenoid valves inside the windchest look like: This is a picture of the original organ keyboard: The large connector found a place on the backside of the case.

The entire circuitry for this robot makes use of five fast PIC controllers: Microchip PIC18F4620 - I/SP types. For each group of 14 notes, a controller takes care of the midi input parsing and the note on/offs, mosfets and conical valve solenoids. There is precise control over the note attack (the velocity byte accompanying each note on command controlling the response speed of the valves) as well as over windflowmodulation during the sounding of a note. This is implemented with polyphonic midi note aftertouch commands and, on the processor level, by applying slow PWM to the holdvoltages over the solenoids. This design was a direct copy of what we did for our <Bomi> robot. Thus, here again, it is important to the user to know that the velocity byte in the midi note-on command does not control sound volume, but only the way the pipes speak. It is strictly an attack control. For detailed circuitry and board population, we refer to the webpage of our <HarmO> robot our since it uses the same boards. Here is the complete circuit for a board serving 14 notes: The PIC firmware however is very similar to what we wrote for <Bomi>, as here also we implemented the PWM steering required for the key pressure control. A sixth PIC microcontroller (a 18F2525 type) takes care of the steering of the windvalve/tremulant as well as of the motor commands and the PWM for the motor controller.

Description of the organ register:

 

Circuit Overview:

Mapping

Midi implementation:

The midi channel for <Pos> is 3 (0-15) or 4 (1-16).

Midi note range: 36- 91. (C-g'') , velocity implemented (steers the speed wherewith the valves do open and hence the note attack). Individual note aftertouch (polyphonic) under development.

Note Off commands are required.

Controller 66 is used to switch the motor on or off.

The tremulant is implemented using a large solenoid working on the bellows. Modulation speed can be set using midi controller 1. Default value for controller 1 when using the tremulant: 64.


Controller 7 is used for the wind pressure (motor speed). The normal setting should be 72. Default startup value in the PIC firmware is 0. It cannot be used for fast wind pressure modulation but is perfectly suitable for slow crescendo and decrescendo. Note however that the pitch as well as the intonation may be affected when <Pos> is operated on nonstandard wind-pressures.

<Pos> responds to the midi all-notes-off command. This command also switches off the lights and the wind valve, but not the motor. To switch off the motor controller 66 should be used.

Technical specifications:

Design and construction: dr.Godfried-Willem Raes (2018)

Collaborators on the construction of this robot:

Music composed for <Pos>:

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Nederlands:

Robot: <Pos>

Voorlopig is geen nederlandse bescrhijving beschikbaar. Zolang we geen strukturele erkenning krijgen van de Vlaamse Gemeenschap zal daar ook niet aan gewerkt worden.

Tessituur:

 


Building logbook / Bouwdagboek:

Omdat ons vaak wordt gevraagd hoeveel werk en tijd kruipt in, en nodig is voor, het bouwen van dergelijke muzikale robots, houden we ook voor <Pos> een beknopt en geilllustreerd bouwdagboek bij:

To be done:


Robodies Pictures with <Pos>:

none as yet.

 


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Last update: 2018-01-07 by Godfried-Willem Raes


Technical data sheet and maintenance instructions:

Board 1:

board output connector pin mapping wire color remarks PIC pin
1 2 note 36 black pulse/hold 4,3
2 3 note 37 brown pulse/hold 2,5
3 4 note 38 red pulse/hold 6,7
4 5 note 39 orange pulse/hold 8,9
5 7

note 40

yellow pulse/hold 10, 37
6 8

note 41

green pulse/hold 36, 35
7 9 note 42 blue pulse/hold 34, 33
8 10 note 43 purple pulse/hold 30, 29
9 12 note 44 grey pulse/hold 28, 27
10 13 note 45 white pulse/hold 24, 23
11 14 note 46 black pulse/hold 22, 21
12 15 note 47 brown pulse/hold 15, 16
13 17 note 48 red pulse/hold 17, 18
14 18 note 49 orange pulse/hold 19, 20

Board 2:

board output connector pin mapping wire color remarks PIC pins
1 2 note 50 yellow pulse/hold 4, 3
2 3 note 51 green pulse/hold 2, 5
3 4 note 52 blue pulse/hold 6, 7
4 5 note 53 purple pulse/hold 8, 9
5 7 note 54 grey pulse/hold 10, 37
6 8 note 55 white pulse/hold 36, 35
7 9 note 56 black pulse/hold 34, 33
8 10 note 57 brown pulse/hold 30, 29
9 12 note 58 red pulse/hold 28, 27
10 13 note 59 orange pulse/hold 24, 23
11 14 note 60 yellow pulse/hold 22, 21
12 15 note 61 green pulse/hold 15, 16
13 17 note 62 blue pulse/hold 17, 18
14 18 note 63 purple pulse/hold 19, 20

Board 3:

board output connector pin mapping wire color remarks PIC pins
1 2 note 64 grey pulse/hold 4, 3
2 3 note 65 white pulse/hold 2, 5
3 4 note 66 black pulse/hold 6, 7
4 5 note 67 brown pulse/hold 8, 9
5 7 note 68 red pulse/hold 10, 37
6 8 note 69 orange pulse/hold 36, 35
7 9 note 70 yellow pulse/hold 34, 33
8 10 note 71 green pulse/hold 30, 29
9 12 note 72 blue pulse/hold 28, 27
10 13 note 73 grey pulse/hold 24, 23
11 14 note 74 green pulse/hold 22, 21
12 15 note 75 purple pulse/hold 15, 16
13 17 note 76 yellow pulse/hold 17, 18
14 18 note 77 blue pulse/hold 19, 20

Board 4:

board output connector pin mapping wire color remarks PIC pins
1 2 note 78 grey pulse/hold 4, 3
2 3 note 79 white pulse/hold 2, 5
3 4 note 80 black pulse/hold 6, 7
4 5 note 81 brown pulse/hold 8, 9
5 7 note 82 red pulse/hold 10, 37
6 8 note 83 orange pulse/hold 36, 35
7 9 note 84 yellow pulse/hold 34, 33
8 10 note 85 green pulse/hold 30, 29
9 12 note 86 blue pulse/hold 28, 27
10 13 note 87 grey pulse/hold 24, 23
11 14 note 88 green pulse/hold 22, 21
12 15 note 89 purple pulse/hold 15, 16
13 17 note 90 yellow pulse/hold 17, 18
14 18 note 91 blue pulse/hold 19, 20

Board 5:

board output connector pin mapping wire color remarks PIC pins
1 2 note 92 grey pulse/hold 4, 3
2 3 note 93 white pulse/hold 2, 5
3 4 note 94 black pulse/hold 6, 7
4 5 note 95 brown pulse/hold 8, 9
5 7 note 96 red pulse/hold 10, 37
6 8 note 97 orange pulse/hold 36, 35
7 9 note 98 yellow pulse/hold 34, 33
8 10 note 99 green pulse/hold 30, 29
9 12 note 100 blue pulse/hold 28, 27
10 13 nc grey pulse/hold 24, 23
11 14 nc green pulse/hold 22, 21
12 15 nc purple pulse/hold 15, 16
13 17 nc yellow pulse/hold 17, 18
14 18 nc blue pulse/hold 19, 20



With the V2.0 firmware in the 18F2525 PIC controller, we get following correspondence between the controller #7 value and the motor frequency:

Controller 7 value Motor frequency

wind pressure

10 mm H20 = 1 mbar

remarks
0 0    
5 8 Hz   no sound
10 14 Hz   motor standby, some pipes can make whistle sounds
15 19.2 Hz   this is the lowest limit for getting the pipes to speak
20 23.6 Hz    
30 30 Hz   pitch may be a quartertone down
40 36 Hz    
50 40 Hz    
55 42 Hz 43 mm H2O good for normal playing, but pitch will be a bit low
60 43.7 Hz    
70 46.5 Hz    
72 47 Hz 45 mm H2O this is the reference value for normal playing, tuning and intonation. A= 440 Hz
73 47.3 Hz    
75 47.8 Hz    
80 48.9 Hz    
85 50 Hz   this would be the nominal motor frequency
87 50.3 Hz    
89 50.5 Hz    
90 50.8 Hz    
95 51.8 Hz 50mm H20 this would be the nominal pressure for the given motor.
100 52.5 Hz    
110 54.2 Hz    
120 55.6 Hz    
127 55.7 Hz 65 mm H20  

The windpressure was measured in the windchest. The pressure measured in the output orifices for the pipes with the valve opened is always slightly lower.

 

Power supply wiring:

Circuit drawing for the midi-input and hub board:

 

Wiring diagram for the above board:

Parts & components: