#linuxcnc-devel Logs

May 13 2018

#linuxcnc-devel Calendar

01:33 PM seb_kuzminsky: https://rwmj.wordpress.com/2018/05/13/xilinx-virtex-7-fpga-bitstream-reverse-engineered/
01:35 PM seb_kuzminsky: might get Virtex 7 support in Project Icestorm soonish
05:11 PM andypugh: pcw_home: (Or anyone else who undertands electronics better than me): Can you suggest a way to interface a probe that swings resistance from 70k to 90k on contact with a 7i64 digital input?
05:51 PM Tom_L: can you do a voltage divider?
05:54 PM Tom_L: i'm not entirely sure that would work there..
05:55 PM Tom_L: you would have to calculate the divider resistance so that 70k would pull it below the trigger threshhold
05:55 PM Tom_L: and 90 would pull it above....
05:58 PM Tom_L: http://www.ohmslawcalculator.com/voltage-divider-calculator
05:58 PM hazzy-dev: andypugh: How bout a schmitt trigger or op amp? Easy and simple
05:59 PM Tom_L: you would still need some sort of divider on the input wouldn't you?
06:00 PM Tom_L: i was gonna say to put the output from the divider close to the trigger threshhold of the 7i64
06:00 PM Tom_L: so that the 70k would trigger it and the 90k wouldn't
06:00 PM Tom_L: or vise versa depending on the logic
06:01 PM hazzy-dev: True, but the schmitt trigger would trigger more reliably than the threshold on the 7i64
06:01 PM Tom_L: i agree
06:01 PM hazzy-dev: Put the schmitt trigger on the probe so there are not noise problems that cause fause triggers
06:01 PM hazzy-dev: false*
06:04 PM hazzy-dev: I have noticed that the analog inputs on my 7i76 drift a lot with temp changes, so I think the threshold on the digitals might to, but I don't have anything to back that up
06:06 PM andypugh: Yes, I would rather like something definite. The probes were built this way, so presumably the manufactuer thought that this was a sensible and robust way to detect triggering.
06:08 PM Tom_L: use it on one side of the divider and find a resistor for the other half for the schmitt trigger's happy spot
06:08 PM Tom_L: then run that to the 7i64
06:09 PM Tom_L: i'm asuming the 7i64 is 5v inputs?
07:19 PM andypugh: 7i64 is 5 to 24V (and works with AC too)
08:34 PM pcw_home: hazzy-dev the analog inputs on the 7I76 should not drift more than a couple percent (but they are not precise since they depend on the 3.3V regulator and 5% resistors)