Scott Hasse wrote: > All- > > I've been attempting to get a simple low-cost frequency-based analog input > to LinuxCNC using an LM331 voltage-to-frequency chip for measuring > temperature inputs from thermistors (as part of my RAMPS board parallel > port adapter I mentioned in a different thread). The good news is that I > have that basically working and will provide a documented circuit once I > get the bugs worked out. Interestingly, when I use the software encoder > hal component in counter mode, I get a lot more variance in the velocity > than I would expect. Yeah, the velocity is jumping up and down about 200 counts from sample to sample! > In my test cases, the pulse rate is very stable, the > pulse frequency is low enough that the parallel port input is capturing > every pulse, and the encoder.0.count is going up linearly as I would > expect. No, it actually is NOT going up all that linearly, it just is at a small enough scale that it looks MOSTLY linear. I see clear artifacts that correspond to the jumps in the velocity trace.
I think there may be some noise or reflections that are causing it to count several times on each proper edge. If the pulse rate is regular, then the velocity should be regular, also, with only a +/- one count fluctuation. Are you running the encoder component's update-counters task in the base thread? If not, it will not be able to handle more than about 1/2 the servo thread rate of encoder pulses. Jon ------------------------------------------------------------------------------ Live Security Virtual Conference Exclusive live event will cover all the ways today's security and threat landscape has changed and how IT managers can respond. Discussions will include endpoint security, mobile security and the latest in malware threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
