[Pd] Serial port out

[Christian Klippel]

hello svante,

Am Freitag, 17. November 2006 18:57 schrieb Svante Hermansson:
> Christian Klippel wrote:
>   > Am Freitag, 17. November 2006 17:26 schrieb Steffen:
> >>
> >> I read about it in Delton T. Horns Music Synthesizers: A Manual of
> >> Design and Construction, if i recall correct, where the author
> >> suggested to use a S/H in connection with such a converter to save
> >> CPU power (when one wanted to keep a given CV for a period of time
> >> (faster then the port)).
> >
> > this is only usefull if you want to digitize a changing signal. you use
> > the s&h circuit (usually just a capacitor and a switch) to "freeze" the
> > current value, so it stays stable while you digitze it. to digitize a
> > signal, you basically need a dac, s&h and comparator. you load the s&h,
> > set a value at the dac, and compare the two voltages with the comparator.
> > you change the dac value so long until you have a match between the two
> > voltages. then you discharge the s&h, and go ahead with the next sample.
>
> Not only useful for digitizing an analog sample into the digital world,
> but also useful as a multiplexer. If you build a converter using one
> single ADC, you could share it to say 8 channels by sending them one at
> a time. Often (but not always) cheaper and easier than using 8 normal
> ADC's. Multiplexing with S&H works even on a low pass filtered
> PWM-signal if thats what someone (?) was planning on using...
>

you are right. but that also implies that the outputs are updated 
periodically, even if the value doesnt change. also, you need a buffering 
op-amp with high input impedance, to keep the voltage stable between the 
updates (a too high load will discharge the cap in the s&h). that continous 
update may also cause some ripple on the output, a thing that needs to be 
considered if you go for high resolution, like 16 bits....

nowdays you can get 8 channel, 12 bit dac's (like the tlv5610) for a low 
price, so i doubt that it is worth going the s&h way nowdays.

greets,

chris

> mvh//Svante - with a homebuilt midi to 8-channel CV somewhere in some
> drawer...
>
>
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