Author Topic: Are there bias resistors on the input signals of the PMDX 424?  (Read 632 times)

Tony Bullard

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Are there bias resistors on the input signals of the PMDX 424?
« on: December 07, 2020, 08:22:07 AM »
I don’t have a board here to test and I would like to connect encoder Index signals from 2 encoders to “Input A” of the PMDX 424. Should I use diodes in the signal lines? They will be used for Probe 0 G31 input. Thanks for any help.


12strings

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Re: Are there bias resistors on the input signals of the PMDX 424?
« Reply #1 on: December 07, 2020, 01:24:19 PM »
According to the PMXD-424 Quick Start guide, section 4.9, there are pull-up resistors on the encoder inputs to "PC+5V" (the guide calls it "L+5V" but the PCB says "PC+5V", this is a non-isolated supply sharing a common ground with the motor step/dir signals).  The manual doesn't say what value the resistors are.  As long as you power the encoders from the PMDX-424's "PC+5V" supply you should be OK.

But... You want to connect TWO encoder index signals to a single input?  Why?  And how are index signals from encoders related to probe motion?  I"m obviously missing something here.  Now if you want to connect two different touch probes to a single input, that MAY be possible if the probes have an open-collector style output.

Tony Bullard

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Re: Are there bias resistors on the input signals of the PMDX 424?
« Reply #2 on: December 08, 2020, 09:31:44 AM »
I have encoders with index pulse on the lead screws and X and Z limit switches. I would like to home on the limit switches then move off to the first index pulse using a probing call, mc.mcCntlGcodeExecute(inst, "G31 X-.5000 f2"), near the end of the refAllHome function. And mc.mcCntlGcodeExecute(inst, "G31 Z-.5000 f2") for Z. Then set Home.

I will use PMDX ("Input A", encoder A signal), X Index signal for the Probe input and "Input B", encoder B, Z Index signal for a user input. In code when the user signal goes high it will set the Probe signal high stopping the G31 move and set home.
I have to verify but I believe the rotary shaft encoders have an open-collector style output. If not I'll use MOSFETS in each Index line.


 

 

12strings

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Re: Are there bias resistors on the input signals of the PMDX 424?
« Reply #3 on: January 04, 2021, 11:41:41 PM »
Sorry - been away for a while.

I don't think you can do the homing and them move off to the first index pulse unless you somehow write your own Lua script to do the "move until index pulse" (if that is possible).  Homing is handled entirely in the SmartBOB (or any motion device).  Mach4 just tells the motion device "home this axis and tell me when you are done."  The PMDX devices have a small "move off" built in to them, might be 0.1" but I'm not sure.

As long as you power the encoders from the PMDX-424's "PC+5V" then it shouldn't matter whether the encoder outputs are open collector or totem -pole.  The 424 will accept either.