MIDI and PICs

[Fraser, Colin J]

> -----Original Message-----
> From: John Speth [mailto:johns at oei.com]
> Sent: 13 May 1999 20:17
> To: 'DIY'
> Subject: RE: simple MIDI keyboard
> 
> I'm curious how you got a MIDI signal out of the PIC.  As far 
> as I know, it 
> doesn't have a dedicated UART.  Did you do the UART function 
> in firmware 
> with the timer?  Lately, I did some calcultions for doing 
> just this.  But I 
> concluded that MIDI in UART functionality would be difficult. 
>  I'd love to 
> see that firmware!

I don't know the specifics of the Roman's keyboard design, but usually you
would step through each bit of the midi byte, plus start and stop bits, and
set the output pin at the correct rate by calculating the clock cycles used
in the output loops and adjusting to get the right timing.

You want to try getting midi into a PIC ;-)

I've had a PIC project on the back burner for months now, but I got it up
and running last night - seems to work OK too.

It's a midi to din sync convertor - nothing new there, but this one runs on
a PIC12c508 - an 8 pin dil chip. 
This chip has an internal clock circuit so it doesn't need a crystal. The
circuit board has an 6N139, 4 resistors, 1 cap, the 12c508, and that's it.
2 connections for a midi input socket, 3 + earth for the din sync out.
The 12c508 costs me less than the opto. The whole thing is less than 5 ukp.

I'll need to make sure it works over a usable temperature range (temp.
affects the internal osc slightly), but if it turns out OK I'll post the
code on the web next week.
It should be easily powered from the midi line voltage, so it could be used
as a 'passive' midi to sync convertor.

I'll post it here in the hope that it will convince a few of the 'I can't
use a microprocessor !' members to give it a try ;-)


Colin f