Slavko Kocjancic пишет: > 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. > Parallel port can take 5v as input, it can't output 5v, only 3.3v. And it's ability to supply current is near 5mA, so your design is at the edge. >> 2. on both sides you have logic levels _always_. >> >> There is little sence to put isolation _here_. >> 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. > I'm talking about inputs, are they capable of accepting 24v? >> 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. > you get 160 signals returning to the same ground, I call it bad design by definition... And yes, your optocouplers are needed here, not between parallel port and the logic. >> 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! > So put your isolation after the MESA, properly done it will have much more value, than your current board. Only it's size makes it prohibitive. > 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. > I thought you were thinking of the board, which might be useful to someone beside you and your simple benchtop machine.
Regards, Alex. ------------------------------------------------------------------------------ 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
