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MIDI Organ Drawbar Control


MIDI Organ Drawbar Controller


This unit is a MIDI Drawbar controller for Native Instruments B4 software. The design uses external faders or potentiometers to physically control the Upper Drawbars, Lower Drawbars and Pedal Drawbars via MIDI Control Change (CC) commands.

A toggle switch is used to switch between operation of the 9 Upper Drawbars and 9 Lower Drawbars The Analog Inputs A0 to A8 are used to send MIDI Control Change (CC) values CC21 to CC29, for the 9 Upper Drawbars, and to send MIDI Control Change (CC) values CC30 to CC38, for the 9 Lower Drawbars, respectively.


Also the Analog Inputs A9 to A14 are used to send MIDI Control Change (CC) values CC39 to CC44, for the 6 Pedal Drawbars.


Note: It is important to connect any unused Analog inputs to Ground, to prevent noise pickup on the inputs producing random MIDI CC Outputs.


This unit can work in standard MIDI mode and via the USB connection. It defaults to standard MIDI Baud rate of 31250. By replacing the original firmware on Mega16U2, the Arduino  will act as a Class Compliant USB/MIDI device.


You don’t need to install additional device drivers on Windows, MaxOSX, and Linux, as the firmware acts as a device of Standard Midi Class. It will automatically install on the system as an Audio USB Device.


The MIDI IN/OUT board also allows the selection of the MIDI Channel from 1 to 16, via the 4-way DIP switches.



midi_in_out_mega.jpg (283771 bytes)


MIDI Drawbar B4 Controller


PRICE:  €75.00




The MIDI Organ Drawbar Controller unit utilizes:

  • An assembled Arduino MEGA unit including a suitable pre-programmed Atmega microcontroller,
  • A 2.1mm power socket, and associated Power LED, 
  • A USB socket for programming and power selection,
  • Select MIDI channel via a 4-way DIP switch,  
  • A MIDI 5-pin DIN input socket,
  • A MIDI 5-pin DIN output socket.
  • 1 toggle switch, to switch between Upper Drawbars and Lower Drawbars operation. 



The MIDI Organ Drawbar Controller also requires:

  • A 9v battery or equivalent DC power source,
  • 9 10k Ohm fader/sliders, for Upper Drawbars and Lower Drawbars operation,
  • 6 10k Ohm fader/sliders, for Pedal Drawbars operation.



Circuit Schematic:

A circuit schematic of the MIDI IN/OUT board shows the Input/Output connections. Arduino Pin D0/RX is connected to the output of the Opto-coupler whose input is connected to the MIDI IN socket. Arduino Pin D1/TX is connected to the MIDI OUT socket via resistor R5. Arduino Pins D2 and D3 provide +5 Volt and 0 Volt(GND) but they need to be set correctly in the software. Arduino Pins D4, D5, D6 and D7 are connected to the 4-way DIL switch, which can be used to select the MIDI Channel (1 to 16). So 8 Pins (D0 to D7) are used  when the MIDI IN/OUT board is plugged into the Arduino Mega board.


Also available is the Arduino Mega board and pin layout.


Also available is some information on setting up the B4 MIDI interface.


Also available is the wiring for the Upper/Lower Drawbar Faders, the Pedal Drawbar Faders and the Upper/Lower Drawbar toggle switch.





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The MIDI IN and OUT connectors use  5-Pin 180 degree DIN sockets. Note that the MIDI IN/OUT wiring is polarised and the correct pins should be used.






Slider/Faders from old Organ:


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There are 3 solder points for each slider/fader, 2 of these are common to all 9 slider/fader controls and they are connected to +5 Volt and GND (Ground) pins. There is also a separate output connection for each of the 9 slider/fader connected to the ribbon.



Wiring of Slider/Faders:


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The 'top' red wires loop to each slider/fader and can be connected to +5 Volts. The 'bottom' black wire loop to each slider/fader and can be connected to GND. The ribbon cable is connected to each individual slider/fader


Wiring of Slider/Faders to Arduino Mega Analog Inputs:


*Click to Enlarge*



MIDI Specification: 

The MIDI channel (1 to 16) is selected by the 4-way DIP switch, shown in Table 1. 


DIP Switch Selections



4 3 2 1
on on on on 1
on on on off 2
on  on  off on 3
on on off off 4
on off on on 5
on off on off 6
on off off on 7
on off off off 8
off on on on 9
off on on off 10
off on  off on 11
off on off off 12
off off on on 13
off off on off 14
off off off on 15
off off off off 16

Table 1 MIDI Channel



Power Supply:

The  Arduino MEGA can be powered via the USB connection or with an external power supply. The power source is selected automatically. The Arduino MEGA draws about 65 mA on standby.


External (non-USB) power can come either from an AC-to-DC adapter or battery. The adapter can be connected by plugging a 2.1mm center-positive plug into the board's power jack. Leads from a battery can be inserted in the Gnd and Vin pin headers of the POWER connector. A low dropout regulator provides improved energy efficiency.


The board can operate on an external supply of 7 to 20 volts. If supplied with less than 7V, however, the 5V pin may supply less than five volts and the board may be unstable. If using more than 12V, the voltage regulator may overheat and damage the board. The recommended range is 7 to 12 volts.