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. > 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. > > 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. 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. -- Kirk Wallace http://www.wallacecompany.com/machine_shop/ http://www.wallacecompany.com/E45/index.html California, USA ------------------------------------------------------------------------------ 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
