MIDI protocol
Principle
Pickup
Frets and strings
Power
Analog part
PIC16x74
COM-port
MIDI-port
Control and indications
Algorithm of note detection
Pickup
In order to detect beginning and end of each played note it is necessary to pick up signal from each string seperately. Therefore polyphonic pickup is to be used. The price for factory-made polyphonic pickup seemed me to be excessive for the first time, while success of total project was very doubtful, and I decided to implement it by myself. By the way, I feared that induced noise on the pickup would be large, but all is OK without shielding etc.
Colleague from
my work, experienced radio-engineer, offered me to try standard beeper as a pickup
sensor. This thing is a tiny dynamic speaker to be installed on PCB. It consists of a
magnetic core winded with a coil of superfine copper wire, all installed in a ferrite cup.
Magnetic membrane lies at the top of the core. When AC is feeded to the coil, it is drawn
to the ferrite cup making sound. All assembly is packed in plastic cylinder. My colleague
adviced me to cut off the top of the corpse down to the cup, throw away the membrane - and
have the pickup. So I did and succeded.
The beeper used is
HCM1216A (in the second model of guitar I used another beeper with less diameter; this
firm is producing a variety of dynamic beepers with different resistance and other
parameters, but these parameters are not much significant for my purpose). Price of the
beeper is $0.55.
Pickup is placed near the stand where magnitude of string oscillation is minimal and string cannot rattle over it. Distance from pickup core to a string is approx. 0.5 mm.