On Dec 18, 2006, at 7:56 AM, [EMAIL PROTECTED] wrote: > Dave Engvall <[EMAIL PROTECTED]> wrote: > >> I keep wondering if there is enough room in the 5I20 to do two servo >> channels plus an extra dac and an adc? >> Or even 3 channels plus the dac and adc; it never hurts to dream. ;-) > > Its not really "two servo channels, a dac, and an adc". Its "two > encoder > counters, three dacs, and an adc". In other words, its just I/O > devices, > be they counters, dacs, whatever. You determined what is a channel by > how you hook them up in HAL. > > Since the stock config provides 4 encoder counters and 4 dacs, you are > already most of the way there. The ADC is the sticking point.
exactly! > > The 5i20 has _no_ analog capability at all, its strictly a digital > chip. It does its "DACs" by generating a high frequency PWM signal > and then filtering and buffering that with an op-amp circuit on the > interface card. Unfortunately that approch doesn't lend itself to > A/D circuits. > > There are a couple of approaches. One that can be quite cheap but is > rather slow, is to take the fourth DAC channel and run it to a > comparitor > along with the analog input, then bring the output of the comparitor > back thru a spare digital input. It would be easy to write a HAL > module > that would increase or decrease the DAC output so it tracks the analog > input. (In fact, you could probably do it using some of the existing > HAL modules - an integrator driving the DAC, with the integrator input > coming from a mux2. Connect the signal from the comparitor to the mux > select input, and set the mux inputs to +1 and -1 so the integrator > ramps either up or down depending on the comparitor setting. Probably usable but limited. > > That approach is only suitable for very slow signals. If better > performance is needed, a real (analog) A/D converter is the way to > go. It could be connected using a bunch of the spare inputs (for a > parallel interface A/D) or just a few (for a serial one). I'm > planning > to go the serial route, with serial to parallel conversion in the > FPGA. > I haven't picked out the A/D converter I'm going to use yet, there are > plenty of choices though. > > For my application, I want several kHz sampling, on three channels, > with at least two of them sampling simultaneously. There are some > simple and cheap ($4) serial 12-bit serial A/Ds from Analog devices. > I'm considering just hooking up three of those, with a common clock > and chip-select/start-conversion line, and three data lines back to > the FPGA. An alternative is a single more expensive ADC chip with > multiple channels. That could use fewer I/O pins, but getting the > simultaneous sampling is a little tougher. Gee! Soft life ... T/H is built in. One KHz would be plenty fast for my app ... but then extra capabilities suggest other projects. :-) And you are going to lay out some kind of circuit board for the a/d's? > > All of this is a few weeks (or months) down the road, I have other > things I need to do first. But whatever I come up with will be made > public under the GPL (FPGA configuration and HAL driver). Sounds neat and will extend the usefulness of the 5I20, etc. Dave > > Regards, > > John Kasunich > > > > ---------------------------------------------------------------------- > --- > Take Surveys. Earn Cash. Influence the Future of IT > Join SourceForge.net's Techsay panel and you'll get the chance to > share your > opinions on IT & business topics through brief surveys - and earn cash > http://www.techsay.com/default.php? > page=join.php&p=sourceforge&CID=DEVDEV > _______________________________________________ > Emc-developers mailing list > Emc-developers@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-developers ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
