[sdiy] Midi2cv with at least 8 channels .. ?

[Grant Richter]

Your refresh rate is equivalent to response time.

The time to update any or all channels should be less than 1 millisecond.

The typical method is to use an interrupt service routine. The output values
are stored in a RAM buffer, your primary application program writes only to
the buffers.

Once every millisecond, the interrupt service routine transfers the content
of the RAM buffers to the output sample and holds.

In order to reduce the cost of the sample and holds, you have the interrupt
routine run at a rate of 1 millisecond divided by the number of channels.
This allow the DAC/switch/cap to settle to more accuracy before moving on to
another channel.

The sample and hold caps actually need to be small, and made of a material
with low dielectric absorption. Dielectric absorption will cause errors if
there is a large change in value for the channel.

A multichannel scanned sample and hold array can be a bit of work to get
fact and accurate. 12 bit resolution is a challenge due to the sample and
hold caps and the limited settling time.

If you can afford it, individual per channel DACs are a lot easier to get
working.

> From: Rob B <cyborgzero at comcast.net>
> Date: Wed, 18 Sep 2002 12:24:24 -0500
> To: Tim Ressel <madhun2001 at yahoo.com>, Seb Francis <seb at is-uk.com>,
> synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] Midi2cv with at least 8 channels .. ?
> 
> As for the refresh, well, with modern components, leakage should be a
> minimum such that you prlly only need to refresh every second or so? I am
> sure you can get around to it by then. :)
> 
> Just use an "any change=refresh" so, no matter *what* changes, you refresh
> *all*.
> 
> I dunno, I have seen a sample and hold hold a good voltage for upwards of
> 20mins with no significant droop..
> 
> 
> Rob
> 
> ----- Original Message -----
> From: Tim Ressel <madhun2001 at yahoo.com>
> To: Seb Francis <seb at is-uk.com>; Rob B <cyborgzero at comcast.net>;
> <synth-diy at dropmix.xs4all.nl>
> Sent: Wednesday, September 18, 2002 12:13 PM
> Subject: Re: [sdiy] Midi2cv with at least 8 channels .. ?
> 
> 
>> I just used 4051s, lm324s and 0.1uF caps for my 8-chan
>> version. Seems to work fine.
>> 
>> --TR
>> 
>> --- Seb Francis <seb at is-uk.com> wrote:
>>> Seb Francis wrote:
>>> 
>>>> I couldn't fine any S&H arrays from my normal
>>> suppliers - maybe I was searching for the wrong
>>> name.  Can anyone recommend any?
>>> 
>>> sorry, forget this question .. I found them now!
>>> was too late at night when I was looking before ;)
>>> 
>>> 
>>> 
>> 
>> 
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> 
>