On Sunday, February 05, 2012 01:28:12 PM N. Christopher Perry did opine: > I'm bringing up my mini-mill and have encountered a weird problem: I'm > trying to use pins 10, 11 & 12 on the printer port as limit switch > inputs for X, Y, Z axes, respectively, but the pins are acting like > outputs. The limits switches are active high, with ether voltage > dividers or diodes in line for level correction and short circuit > protection. When I test the limit switches when not connected to the > PC they work as expected. When connected to the PC a tripped a limit > switch might cause the voltage to move by 0.5V or so, but the voltage > is still held above the TTL high threshold. > > The X-axis limit switch system consists of two OPB972 optical sensors > (TTL level output), which have totem-pole output. Both are diode-ORed > together with a 20K pulldown. > > The Y-axis limit switch system consists of two Honeywell 103SR12A-2 Hall > sensors, which have active source outputs (Open emitter, 12V supply, > ~12 volt active output, floating otherwise). Both are wired together > and put through a 5.1K/2.2K resistor divider. > > The Z-axis limit switch system consists of two Parker Proprietary Hall > sensors (TTL level output), which appear to have totem-pole outputs. > As a precaution, I've diode-ORed them together with a 20K pulldown. > > I’ve got the following motherboard: > ECS TIGT-I2(V1.0) Intel Atom D410 @ 1.66GHz BGA559 Intel NM10 Mini ITX > Motherboard/CPU Combo > http://www.newegg.com/Product/Product.aspx?Item=N82E16813135269 > > I’m running EMC 2.4.6. > > Any ideas? Do I just need lower impedance pulldowns? > > N.C.
Generally, when an input meets std ttl specs, it will take quite a bit lower R's than 20k to pull a std ttl gates input to a logic zero state. I know little about the D510, I have a D525 myself, which is driving a cnc4pc C1G opto isolated interface board and working great. This board claims excellent speed, as in 10ns propagation delays thru the opto stuffs. That seems rather fast for opto's, and I haven't measured it although I have the scope to do it with. Each input is programmable such that its default input is either pulled to the 5 volt rail, or to ground. The pullup or pulldown it presents is in the range of 4.5K to 5.0k, so in that case a 20k pulldown is not likely to be noticed. This isn't germane, but if I were to use a pulldown, I would chose a resistor capable of pulling it down to not more than .15 volts in order to maintain some semblance of noise immunity. That, for the current sourced from a std ttl input, might not be too much over 150 ohms. It is the voltage that counts and even in a completely noise free environment, anything above .6 volts is going to be very erratic. I think most who set limit switches up, wire then as NC and in series. LinuxCNC then only cares that a limit has been exceeded and stops everything. A similar lashup can be used as a single wire home sensor, using only 2 port pins for both functions. Hitting the switch opens the circuit sending a logic one upstream in either event and the home position is set at the center of the tables travel, but can be arbitrary as long is the switches are not tripped again by the move to the home position specified in the .ini file. The limit switch is also capable of being used as a home switch, simplifying that to a one pin input solution. In short, there are quite a few ways of solving that problem, if indeed it is one. But for this, you need to determine the total R it takes to pull it down to at most +0.15 volts when activated. And any 12 volt circuitry needs to limit the logic one to not more than +4.3 volts as some ttl inputs will object to a full 5.0 volt pullup, and nearly all will fuss at 5.5 or more. > ------------------------------------------------------------------------ > ------ Try before you buy = See our experts in action! > The most comprehensive online learning library for Microsoft developers > is just $99.99! Visual Studio, SharePoint, SQL - plus HTML5, CSS3, MVC3, > Metro Style Apps, more. Free future releases when you subscribe now! > http://p.sf.net/sfu/learndevnow-dev2 > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> McEwan's Rule of Relative Importance: When traveling with a herd of elephants, don't be the first to lie down and rest. ------------------------------------------------------------------------------ Try before you buy = See our experts in action! The most comprehensive online learning library for Microsoft developers is just $99.99! Visual Studio, SharePoint, SQL - plus HTML5, CSS3, MVC3, Metro Style Apps, more. Free future releases when you subscribe now! http://p.sf.net/sfu/learndevnow-dev2 _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
