[sdiy] din > midi

[Theo]

Your going from a analogue clock pulse with start /stop lines to a digital
protocol.
Easiest solution would be a small uC (PIC or AVR seem to be made for the
job)

A solution with just logic should be possible too.
The midi timing clock code is "11111000" this midi message has to be sent
every time a DinSync timing pulse arrives.
Add a start bit to the midi message and you get "111111000"
Now consider a midi cable _only_ transporting the midi timing clock message.
The electrical signal looks remarkably similar to a analog clock;
11111110000000000......11111110000000000.........1111111000..............

Now if I don't make a miscalculation here...
Midi works with 31250 bit/sec so the 7 "1" on the midi cable form a pulse of
0,224 msec duration.
Therefore if we can change the incoming DinSync pulse in a fixed pulse of
0,224 msec,
a midi device will see it as a midi timing clock message :)

The circuit can be really simple, but you need a scope to set the pulse
duration.

1) If the analog clock is not at 5V level, get it there.

2) Feed the DinSync pulse into a "positive edge triggered gated one-shot"
circuit.
(think this one is in the top 3 of simple circuits with long intimidating
names)
This is just a Schmitt trigger gate (could be 4093) with a cap in series
with the input and a resistor from input to GND.
Using a 47pf cap the resistor should be a little below 5k,
also a 3k3 fixed resistor plus a 2k pot should get you in the right
direction.

3) Invert the output signal of the above stage (with another gate)
and sent it down the midi lane thru a 220R series resistor.
Don't forget the +5V pin on the midi connector though,
there you also should put a 220R series resistor.

HTH or rather HTW (hope this works)

Theo




----- Original Message -----
Subject: [sdiy] din > midi


> anyone know a quick and easy way to do Din (roland) to midi sync?