[sdiy] Roland DCOs

[Tom Wiltshire]

On 25 Feb 2008, at 17:35, Ingo Debus wrote:
>
> Am 25.02.2008 um 11:53 schrieb Tom Wiltshire:
>
>>
>> What I wanted to know is if anyone has built a DCO along these  
>> lines, and what they discovered. I've wondered about doing it  
>> myself since the 82C54 triple counter chips are only a few pounds
>
> AARGH! The nastiest chip I ever came across!!

I'd be interested to hear why. It looks like a pretty straight- 
forward IC from the datasheet.

>> and the subsequent circuitry is also pretty simple. Alternatively,  
>> you could use the counters on a PIC or similar.
>
> Yes, that's a far better solution. You'd need a processor to  
> control the 82C54 (the C stands for crap) anyway, and the '54 would  
> require a lot of port pins. Perhaps this processor can also  
> generate the voltage that is required for constant output amplitude?

Yes, that's the kind of thing. A single PIC often has more than one  
16-bit timer, so it could generate a couple of DCO square outputs,  
and the amplitude CVs to go with them. That's one possible direction  
to head in.

There's some advantages to doing it with separate counters with a  
single uP to control them all though.

The individual counters can be clocked from different sources (a la  
Oberheim) to stop all the oscillators being locked to a single master  
clock. You'd also have the possibility of running a vibrato LFO or  
overall pitch modulations from the single uP, which is going to be  
tricky to organise with many individual PICs all running separately.

There are advantages and disadvantages to both approaches that I can  
foresee, but there's also bound to be some I can't see. That's mostly  
why I was wanting to find someone who has some practical experience  
who might have a clearer idea of which is really best.

Regards,
Tom