This project is a MIDI controller which can be installed into an existing analogue organ. It is reasonably versatile and could be used as a standalone controller for a set of organ pedals.
I designed this in my first year of university as a cheap way of getting a digital practise instrument at home. Digital organ consoles generally cost upwards of $20K which is prohibit ably expensive for most people while old analogue organs are cheap and easy to find on the internet or at auctions.
I also think that small churches or schools might benefit from having a device like this available to them both as a musical and a learning tool. Virtual organs playing packages such as Hauptwerk are feature packed and can be used to simulater very large organs.
How does it work?
The device sequentially reads the states of every manual key, stop and pedal board and sends midi on/off messages each time they change. It can do a couple more basic things as well.
Where can I buy one?
Not in a store, and not from me. I provide all the information for someone with basic electronics knowledge to build one of these. If you fit that profile, read on. Feel free to contact me if you get stuck or if you want to share photos of the working device.
- A menu system is used to collect data from the operator and also present to the operator the current configuration details. MIDI channels and transposition for manuals, pedalboards and stops can all be configured via this interface.
- An easily expandable system for identifying each device in the system and reporting the states of each “switch” in that particular device and
- Finally, a system for sending the MIDI out messages.
The menu system consists of an LCD display and 4 pushbuttons (“down”, “up”, “next” and “previous”). All configuration of the system is done via these four buttons. On “boot” of the device, the LCD displays first the version number of the current firmware, then it proceeds to display a short description of each device (by device, I mean a manual, peadalboard or set of stops) that it has detected which is attached to the system (these messages are purely for testing purposes while building the system). After these messages have been displayed, the LCD will display the first menu item and the device will be operational.
The device chain is a set of parallel-to-serial shift registers which have their inputs connected to every single key/stop/pedal in the organ. To make the device capable of being installed in any organ with any combination of pedals, stops or manuals without it being necessary to make a different version of firmware, there is a single 8-bit shift register inserted at the start of each device in the chain to provide “header” information about the inputs that follow.
An example device chain:
[Controller]<–[8 bit header]<–[key states for pedalboard]<–[8 bit header]<–[key states for manual 1]<–[8 bit header]<–[key states for manual 2]
The header consists of two bits which identify the type of device (manual, pedalboard, stopboard or termination of device chain), 4 bits that describe the number of keys that device consists of, 1 bit to state if the device is a toggled and 1 bit to state if the device wants feedback (i.e. wants to know if its down or up). See the following table for more information:
|Bits 6 – 7||
The state of these bits defines the type of device attached to the system
Possible combinations: (bit 6 to bit 7)
|Bits 2 – 5||
Device key count
This numeric value of these four bits is basically the number of 8-bit shift registers which follow holding the key states minus 1.
Examples: (bit 2 to bit 5)
Request feedback bit
If this bit is HIGH, the device also contains a set of serial-to-parallel shift registers which want to be sent the state of each key in this device. If it is LOW, no feedback information is used. Similarly to the toggle bit, this feature is only really useful on stop boards with momentary switches where you want a LED to be illuminated when the stop is active.
If this bit is HIGH, the note on and off messages are sent every-time a key completes a full up/down cycle. That is, the key will become “push on/push off”. If it’s LOW, the keys function normally. This feature is only useful on a stopboard with momentary switches.
Note that this assumes that the parallel-serial shift registers all send the MSB (i.e. bit 7) first.
Schematic Diagram for the Controller.
Important: The LCDCON and LCDDATA connectors in this schematic are used to connect a KS0066 LCD module to the device. LCDCON pins 1-6 connect to the LCD modules pins 1-6 and LCDDATA pins 1-8 connect to the LCD modules pins 7-14. Pins 15-16 of the LCD module are for the backlight of the LCD and are optional to connect. KS0066 LCD modules are readily available from Jaycar in Australia for about AU$20.
Below is the pinouts for the “keybus” (the name for the connections which interface to the shift-registers):
|Keybus Pin Number||Description of Pin|
|3||KBCLK – Connect to ALL shift registers CLK pin|
|4||KBPL – Connect to ALL shift registers PL* pin|
|5||KBDIN – Connect to the first headers D7 (data out) pin|
|6||KBDOUT – Connect to the first serial-parallel SER (data in) pin|
* active low signal.
I have chosen these pinouts as it makes expansion simple (if pedal/manual/stop boards are designed similar to the examples below). Each device can have an input and an output keybus socket, pins 1-4 can all be joined directly (there is a limit to how many devices the clock and pl signals can interface to – I have tested it with 14 74HC165’s and it still works fine – for more, buffers can be used) and pins 5 and 6 are kind of obvious (if a device has no feedback information, pin 6 can be connected directly to pin 6 as well).
Examples of two keybus devices
PIC Firmware Downloads
14th December 05
V18.104.22.168 Source code and compiled HEX file for the V1.0b controller board
4th December 05
V22.214.171.124 Source code and compiled HEX file for the V1.0b controller board