Active Low inputs on MESA 7i77
- deerefanatic
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18 Nov 2021 01:39 #226819
by deerefanatic
Active Low inputs on MESA 7i77 was created by deerefanatic
Hi all,
As I continue my project to setup my Wotan HBM, a new challenge has presented itself. The homing and soft limit switches are all wired to a common ground and were setup as active LOW on the old CNC controller. To avoid having to do a large amount of rewiring, I thought of just wiring a small circuit board that has 10k ohm pull up resistors to pull the outputs to +24v when the switches are open circuit and let the switches ground it out to 0v when they are active. Then just invert the state in LinuxCNC.
Do you see any issues with doing it this way? I can't think of any negative effects this would have on operation, or the daughtercard itself. At 24V, a 10k resistor would only flow about 2.5 milliamps of current.
As I continue my project to setup my Wotan HBM, a new challenge has presented itself. The homing and soft limit switches are all wired to a common ground and were setup as active LOW on the old CNC controller. To avoid having to do a large amount of rewiring, I thought of just wiring a small circuit board that has 10k ohm pull up resistors to pull the outputs to +24v when the switches are open circuit and let the switches ground it out to 0v when they are active. Then just invert the state in LinuxCNC.
Do you see any issues with doing it this way? I can't think of any negative effects this would have on operation, or the daughtercard itself. At 24V, a 10k resistor would only flow about 2.5 milliamps of current.
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- tommylight
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18 Nov 2021 02:57 #226821
by tommylight
Replied by tommylight on topic Active Low inputs on MESA 7i77
That is correct and there are no drawbacks.
The only somewhat important thing is to have the switches normally closed so in case of a wire cut the machine will not work.
The only somewhat important thing is to have the switches normally closed so in case of a wire cut the machine will not work.
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18 Nov 2021 07:31 #226842
by rodw
Replied by rodw on topic Active Low inputs on MESA 7i77
I just checked my notes. I used 2.2k 1W pullups based on recommendations from PCW on my 7i76e for NPN prox sensors.
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18 Nov 2021 10:29 #226849
by bevins
Replied by bevins on topic Active Low inputs on MESA 7i77
You take notes?I just checked my notes. I used 2.2k 1W pullups based on recommendations from PCW on my 7i76e for NPN prox sensors.
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20 Nov 2021 05:59 #227053
by rodw
Replied by rodw on topic Active Low inputs on MESA 7i77
Best thing I ever did was document every pin before I wired it in a table. As I've done upgrades and changes I keep it current.
I just checked my notes. I used 2.2k 1W pullups based on recommendations from PCW on my 7i76e for NPN prox sensors.
You take notes?
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- deerefanatic
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28 Dec 2021 23:22 #230185
by deerefanatic
Replied by deerefanatic on topic Active Low inputs on MESA 7i77
To put a finish on this thread, I'm using 3K pullup resistors on a 24v power supply and it works great! Thanks for all the help.
The following user(s) said Thank You: tommylight
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