3.2
Keyboard contacts debouncing - #99
Every kind of contact bounces sometimes. This is very short series of contact
closures and openings, making instable signals for detecting key on and key off. To
prevent the controller from sending MIDI notes on every bounce, a special
technique is performed, called debouncing. All boards from midi-hardware.com
perform contact debouncing, but MBBS also provides possibility to adjust the
strength of this process. By default debouncing is set to 20ms, but you can change
it to one of 10 steps from 2ms to over 40ms. If there are no bouncing effects
apparent in your keyboard, there's no need for long debouncing, and it can be
shortened to reduce latency. But wwith old rusty wire contacts, it may be necessary
to set the debouncing to a higher level. This increases latency, but prevents from
burst of unwanted notes with every key going up or down. To change debouncing
time, you must play any note on the keyboard connected to internal inputs of MBBS
(not on the scanners) and use command #99x, where 3rd digit (x) determines
debouncing strength. 0 means almost no debouncing and minimum latency, while 9
is maximum debouncing and biggest latency. See chapter 5 for general guidelines
on how to enter commands. If you have dedicated LCD module -
MiDisp, this
setting is easier to follow because short prompts are displayed after each digit.
4
Potentiometers & Control Voltages
Pot inputs are available with use of proper expanders, like POT12, BBS24, PDS or
BBSP. They can be used as continuous controllers for things like volume,
modulation etc. Usually those inputs would be connected to potentiometers, but it's
possible to use them as analog inputs with range of 0..+5V. Applying voltage of 0V
causes generation of CC with lowest value, while +5V makes highest possible value
of assigned MIDI parameter. Each input in the system has separately assigned MIDI
event and channel. This assignment can be easily changed by the user with use of
special programing keypad, or lowest 10 keys of any connected keyboard. Every
potentiometer scanner is described in chapter 7, with connection schematics.
All potentiometers must be linear taper (not audio) in range 10-50k,
preferably 20k.
If there are 2 or more potentiometer scanners in the system, they must be chained,
i.e. first board is connected to MBBS, and second one is connected to first POT
board, etc. If you use 2 inputs of MBBS to connect POT boards, they both will share
the same settings. That means it would be like having 2 potentiometers for the
same MIDI parameter on the same channel. The chain of potentiometer scanners
can be connected to any one of the MBBS inputs, or any daisy-chain input of other
connected scanners, but only one. Only keyboard scanners can be connected to all
inputs at the same time. You can mix different kinds of POT scanners in one chain.
There can be for example two POT12, and BBSP at the end. The
total number
of
potentiometer inputs should
not exceed 64
. All additional inputs will be ignored.
Every POT scanner has pins for connecting outer leads of the pots. They are
7
