On 04/01/2014 11:27 PM, Gregg Eshelman wrote: > Now back to the question, now that it's established exactly what kind of > signal the scales and encoder put out. > > What *hardware* do I need to interface them safely with a PC? I've read > that it's "simple" to connect "directly" to a parallel port and a garden > variety LPT can handle two quadrature inputs. The parallel port (and software encoder counting) has a speed limit. You run a BASE_THREAD at some rate, and the encoder cannot produce counts even approaching that rate without the risk of occasionally missing a count. So, it the BASE_THREAD is at, say, 50000 (which is 50 us or 20 KHz) you can't reliably count more than, perhaps 15,000 counts/second. If you have a 10 um scale, that's a count every .01mm of movement. 15 KHz is 150 mm/second or 9 m/min (5.9 IPS or 354 IPM). Not much of a limit. But, if the scale is a 1 um, then you are down to 15 mm/sec or .9m/min (35.4IPM) which would start to annoy people. So, you have to do the calculations for your specific computer and encoder resolution.
Or, you could get a Mesa or Pico Systems board to handle the encoder counting in hardware. This relieves the computer of the heavy interrupt load of sampling the encoder, and also gives you better step pulse generation or servo command. Jon ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
