32 outputs MIDI Decoder

Here is the description a 32 outputs MIDI able to switch relays, electromagnetics devices... in order to automate a mechanical musical instrument, or command lights...

Principle and Schématic

MIDI datas from a musical instrument equipped with an MIDI output or from a sound card of a computer
are analyzed by the software present on the PIV 16F84.

Optocouplor IC10 (1N136) ensures the galvanic insulation.
The outputs of PortB form a 8 bits parallel bus data towards the four 74LS574 (8 Latches),
the outputs of PortA 1,2,3,4 order the memorizing of these 74LS574
Buffers ULN2803 make it possible to control loads until 2 A .
The power supply 5V is articulated around a regulator 7805.
Connector CN7 receives the power supply from 9 to 24v according to the type of relay or electromagnet.

while clicking on the diagram you reach the shéma in large size.
this diagram is made with
ExpressPCB , (Freeware)

Components list

R1 220 Ohms 1/4W
R2 3,3K 1/4W
R3, R4 1 K 1/4W
R5 470 Ohms 1/4W
R6 ... R9 10 K 1/4W
SIL1 ...SILl4 1K R-sil-09
C1 1000 Radial uF 40V
C2, Radial C3 10 uf 16V
C4 ...C9 100 nF 63V
C10, C11 33 PF 63V
Q1 Quartz 8 MCHz HC18U
LD1 ...LD32 LED red D3
LD32, green LD33 LED D3
D1 1N4148
P1 Pont W04
Transformer TR1 230V/2X6V 3VA or 1X12V 3VA
F1 Support of fuse and fusible 200mA
CN1 ...CN4 connector block 8 points with screw
CN5 DIN 5Br frame 45°
CN6, CN7 connector block 2 points with screw
REG 7805
IC1 16F8Â
IC2... IC5 74LS574
IC6... IC 9 ULN280Á
IC10 Ñ136


For a facility of realization the printed circuit is a simple face with some straps.

I use LAYO1 (the version of demonstration is free). here the file with the Layo1 format: decomidi.pcb and GIF: ci_decomidi.gif



The output from 1 to 32 correspond to the G low (1) and D high (32).
the relay or electromagnetic device is wired between one of these outputs and the +12V of auxiliary power
Be carefull !! dont forget to wire the four 10 K resistors (R6 to R9) on the back
of the printed board (pin 11 of each 74LS74 and +5V)


the sofware, made in assembler for PIC 16F84A, was developed with MPLAB of Microchip .
It is downloadable in format
ASM or HEX for direct programming of the PEAK (with Ic-prog for example)
and a programmer:

The data arrive on PortA.0 which is scanned permanently.
Dice that the code Notes ONE on channel 1 (90) is detected the program analyzes the MIDI code N° 2 which corresponds to the height of the note (69 is equal to the 440Hz) and valid the corresponding output
The MIDI code N°3 (dynamics) is not used.

If a code MIDI Notes OFF (80) the output goes down
it is possible to play until 10 notes at the same time.

At the power up fours notes are actived for a short moment (C,E,G,C)

Tessiture and Test of the notes (useful file MIDI to test the chart)

a very complete program to create and publish partitions, to modify files MIDI:

Melody Assistant

Contact E-mail: contact@victorseraphine.com