[sdiy] Last chance for 4xD PCB order

[Andre Majorel]

On 2006-07-16 19:01 +0100, Seb Francis wrote:
> Andre Majorel wrote:
>
> I do like dedicated boxes that do a specific job well, with 
> zero-latency, plenty of knobs and dedicated I/O.  Since lots of my 
> hardware is analog and can never (not yet anyway) be reproduced 
> faithfully inside my PC, having external digital effects with 
> zero-latency and dedicated I/O makes a lot of sense.

Ah yes, zero-latency is a point.

> >Seb you have already said that VC could be added. I'll try to be
> >a bit more specific this time. What would it take (number of 4xD
> >PCBs and approx. magnitude of software and hardware changes) to
> >have :
[...]
> (2) You need to add an interrupt service routine to sample the analog 
> inputs at the desired sampling rate (hardware-wise this is 100ksps per 
> CV, but maybe the available CPU time would make a lower limit - I didn't 
> work it out).  This ISR would then simply call the same internal 
> function that gets called when a parameter change is received over SPI 
> from the UI PIC.  The limitations are that there is no bi-directional 
> communication between the dsPICs and the UI PIC so any parameter changes 
> made by CV would not update the LED display, internally held rotary 
> encoder positions or flash RAM.  I did think about allowing the UI PIC 
> to receive CV control, but I decided it would be better to sample the 
> CVs directly on the dsPICs, allowing higher sampling rate and avoid the 
> SPI bottleneck.

The loss of the delay time display is a minor shame but I can
live with that. I'm sold. I'll contact you off-list. Thanks a
lot for the explanations, even if I rudely snip them off.

> >If adding VC delay involves sacrificing rotary encoders, that's
> >fine ; once I have VC, I expect I won't have any use for them
> >except perhaps a coarse delay range control per channel (and
> >even that might not be needed at all).
> 
> Well, this is another option: sacrificing rotary encoders will give you 
> 2 CV inputs to the UI PIC per sacrificed encoder (up to a maximum of 8 
> CVs).  But doing it this way you would need to provide your own CV input 
> buffers off-board, and the achievable max sampling rate and resolution 
> would be lower.  On the plus side though, you could update the LED 
> display, internally held rotary encoder positions and flash RAM from the 
> CVs.

So ditching the rotary encoders and routing each CV input to
both the SPI and the UI PIC, we could have both VC delay time
and delay time display, yes ? Not exactly your original intent,
I know, but addressing two markets with one product is success.
:-)

The sampling rate and resolution limits are non-issues here, I
think. It would be nice to have sub-ms display precision for
short delays, but so would having it delivered to me by a group
of promiscuous, scantily-dressed girls.

-- 
André Majorel <URL:http://www.teaser.fr/~amajorel/>
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