simple sample/hold circuit?

[Rene Schmitz]

Hi Andy!

At 11:58 02.10.99 -0500, you wrote:
>My question is, what's a good way to
>do sample and hold on the DAC output so that I can scan through all the
>outputs using a single DAC?  I guess it doesn't need to hold for very long,
>but I haven't written the PIC code yet so I don't know how long it needs to
>hold for.

In my multi output (up to 80!) printerport CV convertor I've used 4051s
with 22n MKT (=mylar) caps and TL084 as buffers. Works pretty good, the
hardware side is done, but my software is not yet ready to publish it.  The
caps hold a few seconds without serious droop. I think an update frequency
of 10-100Hz will be more than sufficient.
 
With the PIC I would not use the timer, but just do a refresh loop forever,
and use an interrupt to jump into the routine which receives and processes
the data. Otherwise one would run into problems doing a software uart.
Constancy of the update frequency is not required. 


Bye
 René



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