Alexey Starikovskiy pravi: > As a matter of fact, I already see a big stopper in your board usefulness. > You put optical isolation between logic and parallel port, I see 2 > drawbacks of it: > 1. parallel ports are quite weak these days (3.3v/~5mA), so driving LED > from it directly is not bullet proof. > All EPP ports are 5V tolerant and I didn't see the EPP port diferrent as open colector with pullups. LED are arranged to be driven low with external 5V supply. And optocoupler is happy with anithing from 5mA up to 20mA. So I see no problem. > 2. on both sides you have logic levels _always_. > ??? > 3. machine equipment on the other side of your logic has very different > set of voltages, > 12, 24 volts are common, and sometimes you could find 48, your board > does not allow to > connect this equipment without yet another layer of optical isolation. > I'm setup machines without problems on that. The board need 12V unregulated for relays only If you have no relay then anithing betwen 8V to 30V is good. > 4. now you have common ground between all your logic and all 48 inputs > and outputs > (and your schematics can be stretched to 160)... I doubt that you could > keep such ground > clear of the machine noise. > The bad design has big ground loop noise. If somewhere is that problem then just put normal optocoupler just here. > In general, your design seem to be very close to UBOB board here: > http://www.candcnc.com/UBOB.htm > Seems similar. But my board rely on EPP interface to not stall computer. One cycle LPT port take near 1uS! And I need only 1 per byte. UBOB needs at least 3. And price is way overpriced. All thing for my plate is under 25Eur. (with homemade pcb) > The problem with the above seems to be it's price, for about same money > its possible to > get much more capable board from MESA -- 7i43. > Yes MESA is good ... .. but without isolation at all! Any time I have problem with ground loop problem the relation PC <--> Machine is the worst one.
Anyway I don't want to argue is it good or is it bad. Just want simple solution for simple benchtop machine. Slavko. ------------------------------------------------------------------------------ Download Intel® Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
