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Spider RooM Labs


MIDI to Sync24 converter

Features (version 2.31 - final version):

 - 9 tempo outputs: 48 ppqn (see shout out below), 24 ppqn, 8 ppqn, 4 ppqn, 2 ppqn,
                     1 ppqn, 2 ppwn, 1 ppwn, 0.5 ppwn
 - Roland type Start/Stop and Continue outputs
 - Sync24 DIN socket
 - works up to 360 BPM (tested with Roland TR-606) ;->
 - optional MIDI Thru socket and MIDI activity LED


PCB - component side
PCB - solder side

Program, source, and some additional text files (version 2.31)

Part list:

Resistors (1/4W carbon or metal film):
1x 220R
1x 360R

2x 220R (optional)
1x 1k2 (optional)

2x 22pF ceramic
1x 10nF ceramic multilayer
2x 47uF/25V electrolytic

5x 1N4148
1x LED of your choice (optional)

1x PIC16F84
1x 6N137
1x 78L05
1x 74HC14 (optional)

1x 4MHz cristal/resonator
1x 18pin DIP socket
1x 14pin DIP socket (optional)
1x 8pin DIP socket
3x DIN 5pin connectors
10x 1/4" or 1/8" jacks
1x connector for power supply of your choice

1x PCB (or protoboard)
1x case to put everything in
1x Power supply (up to 18V DC or 12V AC)

Circuit description:

    This is pretty much straight forward. MIDI input is separated
from the rest of the circuit by an optocoupler. The signal from the
opto is then passed to PIC and - optionally - to 7414 hex Schmitt
inverter, which drives MIDI Thru and activity LED.
From the PIC, the 24 ppqn tempo, Start/Stop, and Continue lines are
connected to the DIN Sync socket. All the lines go to PCB connectors
which can be fitted with 1/4" or 1/8" connectors on the front panel.

PIC program description:

    Since the PICF8x lacks the UART, it must always run in 32us loop
to read MIDI line properly (1/32us = 31250 baud); at 4MHz cristal that
means looping on 32 machine clocks. First it has to synchronize into MIDI
stream, so that it does not cause any misreading and faulty commands.
Second part of the program is the main loop in which PIC checks for MIDI
bytes, filters out anything unwanted, and makes appropriate changes to
output pins.

Using the device:

    DIN sync converter is used to sync some of pre-MIDI drum machines
and sequencers (e.g. all those X0X Roland boxes) to MIDI. Additional
output jacks are used for synchronizing other devices (e.g. analog

    Connect device to MIDI and to device you want to synchronize
using either DIN Sync or jack outputs and start your MIDI sequencer.

    Note that 24 and 48 ppqn lines are running all the time (if there
are incoming tick messages, of course), while other lines will start
running on Start message and end running on Stop message.

Shout out:
    While this project was in a testing phase I stumbled across a
site of John Tuffen with a description of a similar device to this.
    There I found his signal chart for 48 ppqn line, which at that
point I haven't implemented. I took his idea and made my own code
for 48 ppqn line simulating the behaviour seen on his page.
    This is also the reason that I've put the source for this project
online, since I wanted to make it obvious that I did not steal his

(C) 1999-2000 Bojan Burkeljc
Last update: 11th August 2002