[sdiy] DIY MIDI clock to sync pulses

[Colin f]

> > Can any recommend me a simple midi clock to sync pulses circuit,
> > preferably PIC based?
> >
> 
> You could check out http://ucapps.de   I'm pretty sure the boards
> there can do what you are after and quite a bit more.

One thing to be aware of with MIDI to DIN conversion is that if you are
using certain PC-based sequencers, you cany have sync problems.

DIN sync clock pulses need to last at least 2ms, though nearer 4ms gives
better reliability.
You also need to have a gap of at least the same minimum duration between
pulses.

Now, some sequencers send MIDI clock pulses at the correct *average* rate,
but quite often they will bunch a few together, rather than spacing them
accurately.
The result of this is that if you simply trigger a pulse when the PIC
receives a clock byte, the pulses can end up overlapping, and you lose sync.

What you need to do is have a counter that is incremented each time a MIDI
clock pulse arrives, and another process to generate the output pulses no
faster than the maximum rate.

This isn't a problem with all software sequencers, but if yours is affected,
you may struggle to work out why your simple DIN chip isn't keeping sync.

Cheers,
Colin f