Parts list & Description: 

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

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

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

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

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

Other: 
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 
sequencers). 

    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.