On May 26, 2012, at 7:55 PM, Kirk Wallace wrote: > On Sat, 2012-05-26 at 13:45 -0600, Jeshua Lacock wrote: > ... snip >> Interesting. So the pull down resistor would go on the encoder ground? > > No, between the encoder input terminal for each input having a problem > to the ground associated with the input. This will lower the input > impedance so the noise will be pulled closer to ground and also lower > than the trip voltage. On the other hand it may also lower the ON > voltage so the resistor needs to be high enough to keep the ON voltage > above the ON trip point for the input. The minimum resistance should be > higher than the current limit of the encoder output limit. If the > encoder output current limit is say 10ma at 5 Volts, then V = I R and 5 > = .010 x R or R = 5/.01 = 500 Ohms. In this case 500 Ohms or higher > could be used. You encoder may have different specifications.
Great, thanks for the great information Kirk! Just because I am dense (or overly cautious), the resistor would go between the A signal wire in my enclosure to the encoder power ground? Then the B signal wire also to the encoder power ground? So I guess if it is less than the minimum voltage, it is just sinked to the ground? Very cool. >> Was it connected at the control box end? I don't have much >> electricity knowledge (no surprise there), so could you recommend what >> size the resistor would be? > > Look for the encoder output current limit and working voltage and use > Ohm's law as above as a guide. Maybe, double the resistance, say 1k Ohm, > and see if it helps. An oscilloscope would be handy to see what the ON > and OFF voltages are, but a voltmeter might be good enough to check the > a continuous ON and OFF. The specifications for the input might call out > what the ON and OFF voltages are. It might be that OFF needs to be lower > than 1 Volt and ON higher than 3.5, but it could be different by quite a > bit. The encoder I have is in-fact 10ma max, 3.5-5v (I am giving it 5v though): http://www.amtencoder.com/Product/AMT102 I think I have a bundle of 1k resistors laying around. >> What size capacitor? Was it connected between the encoder DC +5v and >> ground? Was it connected at the encoder end or the control box end? > > I believe I put my capacitor in parallel with the resistor, which is > probably not proper. With the capacitor connected from the input pin to > ground, will for a brief time act like a short circuit and could draw > too much current from the encoder. My capacitor is small enough that the > high current doesn't last long enough to hurt anything. The TI document, > I linked earlier, shows the capacitor in series, or wired such that the > input pin goes to the resistor, then to the capacitor, and then to > ground. This has the advantage of having the resistor limiting the > current. As the the capacitor charges the effective resistance goes > from, let's say the example 1k Ohms, then higher. The capacitor stores > and releases voltage so that it tends to try to keep the signal voltage > constant. This can drown out fast noise spikes, but if the capacitor is > too large, it can also drown out fast encoder signals that you may want > to keep. If the resistor alone doesn't help, add the capacitor . Maybe > try .01 microfarad. An oscilloscope will be needed to see what the cap > does to your signal. Interesting! I don't have an oscilloscope, but its something I have been wanting. I think the changes I have made got the axis in-check, but it still seems a bit noisier than I would like. So I will try the resistors first. > Others on this list have a lot more experience with this, so if any of > the above is wrong, hopefully someone will speak up. > > I don't recall what your encoder and input hardware is. I may be able to > narrow down some of the above, if you post this information. Oh, and > also the encoder signal rate. The encoder data sheet states 250 kHz max. I am using Pico Systems USC with the Gecko interface and Gecko 320s (the non-X type). Thanks again, Jeshua Lacock Founder/Engineer 3DTOPO Incorporated <http://3DTOPO.com> Phone: 208.462.4171 ------------------------------------------------------------------------------ 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
