MIDI Boutique mdbc24 User manual

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mdbc24
24 potentiometers (drawbars) MIDI encoder
* user’s guide *
1 Purpose
mdbc24 is a small electronic unit, designed to be
incorporated into MIDI consoles/drawbar boxes intended to
control standalone MIDI expanders/synthesizers by MIDI
messages. It can scan up to 24 potentiometers and encode their
position change in proper MIDI messages ( ontrol hange
messages in typical case). Each potentiometer has proper
message assigned. There are 2 user-selectable banks of such
messages. The scanrate per potentiometer is user-selectable as
well as the MIDI channel. Table 1 and Table 2 show the possible
user settings. Upon special order the unit can be programmed
for different sets of MIDI ontrol hange or other types of
MIDI messages.
The unit has MIDI input and MIDI output. The MIDI messages
that are received on MIDI input are merged to the messages that
are generated by the unit itself. The merged MIDI stream is
transmitted as-is, without mapping to the unit’s MIDI channel.
Merger supports all kinds of MIDI messages, including SysEx and
Realtime messages. In case when running status messages arrive
on MIDI input, they are reconstructed by the unit (status byte
is added) and then merged.
2 Settings
All settings of the unit can be done by means of onboard
DIP switch. User can change the MIDI channel for all events
triggered by the unit by means of bits 5,6,7,8 of DIP switch
(numbers according the labels on DIP switch). These settings
are described in Table 1. The scanrate is adjustable by means f
bits 1,2,3,4 of DIP switch according Table 2. The bank of
continuous controllers is selectable by means of switch or
jumper according the wiring diagram at the end of this
document. Upon changing any of DIP switch bits or Bank
selector, the changes take place immediately and there is no
need to restart the unit for using the new settings.

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Table 1. Setting the MIDI channel
DIP switch
Bit 4 Bit 5 Bit 6 Bit 7
MIDI channel
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 2. Setting the Scanrate
DIP switch
Bit 1 Bit 2 Bit 3 Bit 4
Scanrate
(times per
second)
On On On On 400
On On On Off 244
On On Off On 173
On On Off Off 135
On Off On On 111
On Off On Off 94
On Off Off On 81
On Off Off Off 72
Off On On On 64
Off On On Off 58
Off On Off On 53
Off On Off Off 49
Off Off On On 45
Off Off On Off 42
Off Off Off On 39
Off Off Off Off 37

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Table 3. Selecting the Bank of controllers
Bank Switch Selected is
Off Bank 1
On Bank 2
NOTES:
• The positions shown in red are the factory presets.
• The settings can be changed during the use of the unit and
will take place immediately.
• The change of the MIDI channel does not affect the MIDI
stream being merged. If there are a MIDI messages coming on
different channel than the unit’s channel, they will be
simply re-transmitted on their original channel, regardless
of the MIDI channel set by user (no channel mapping).
Table 4. Standard MIDI Controllers
assignment (can be different on custom
request!)
Potentiometer
MIDI Message
for Bank 1
MIDI Message
for Bank 2
1 07 12
2 11 13
3 12 14
4 13 15
5 14 16
6 15 17
7 16 18
8 17 19
9 18 20
10 19 21
11 20 22
12 31 23
13 66 24
14 67 25
15 70 26
16 72 27
17 73 28
18 74 29
19 75 33
20 76 34
21 78 35
22 79 36

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23 80 37
24 90 38
NOTES MIDI ontinuous ontroller ( ) message consists of 3
bytes:
- byte1:carries message type identifier (4 bits) and MIDI
channel number (4 bits);
- byte2:carries the number 0-127 (shown in table above);
- byte3:carries the encoded position of the proper
potentiometer in range 0–127. For good potentiometers
response, it is recommended linear potentiometers to be used.
4 Wiring
Before use the unit should be wired according the wiring
diagrams shown in Appendix A or Appendix B. The power supply
can be any A /D adapter capable to source 100mA or more at 9-
12 Volts. Potentiometers should be linear 2-100 kOhm. All 24
potentiometer should be of same resistance. Sliding or rotary
potentiometers can be used as well. Drawbar sets of Hammond
style can be used instead of potentiometers as shown in wiring
diagrams.
5 Technical parameters
The main technical parameters of mdbc24 are listed in Table 5.
Table 5. Technical parameters
Parameter Value Uni
t Comment
Power supply
voltage 9-12 A /D V
Power supply
current 50 mA
Adaptor or
transformer
Max number of
scanned
potentiometers
24 -
Not used inputs are
read as potentiometer
at max position (
value 127)
Scanrate 400-37 S
-1
User adjustable
MIDI messages (see Table
4) - In two banks
MIDI channels 1 – 16 - User selectable
Approx size 9.5 x 7.1 cm 3.76” x 2.8”
Weight 52 g 1.8 oz

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Appendix A Wiring for potentiometers

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Appendix B Wiring for Hammond-style drawbars