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... > > > _______________________________________________ > PD-list@iem.at mailing list > UNSUBSCRIBE and account-management -> > http://lists.puredata.info/listinfo/pd-list _______________________________________________ PD-list@iem.at mailing list UNSUBSCRIBE and account-management -> http://lists.puredata.info/listinfo/pd-list