Hal Meter Question

Hello all,

I hope I have the correct forum for my question.

I am in the process of writing a tutorial and I want to make sure that I have my information right and I think someone here would know.

If I am in the Stepconf Wizard, and select Probe In for pin 15, I will end up with two lines added to my machine's hal file.

net probe-in => motion.probe-input
net probe-in <= parport.0.pin-15-in

Now I understand that the signal probe-in gets it value from the parallel port pin and send its value along to motion.probe-input.

Now, if I start LinuxCNC (running Axis) and go to the machine menu and open Hal meter, and select the probe-in signal, I will either get a TRUE or False value.

This value that I see, is it the actual logic value of the pin? In other words, If the value reads true, it would indicate that the pin is pulled up to 5V internally and if the value is False, the pin is pulled to ground internally? By internally, I mean by either the parallel port on the computer itself or the breakout board that is buffering it?

I am writing a tutorial and a series of videos for configuring LinuxCNC to use a touch off plate. I know that this has been covered in quite a few places, but i thought I would give a bit of a different angle on it, covering the actual configuration additions and changes that have to be made to make it all work and happen. I though I would cover both using Stepconf Wizard and manually editing the HAL files, for both implementation methods using o codes and classic ladder.

My approach is to start at the beginning, identifying an available input pin on the parallel port, adding it to HAL, testing the pin to see where it is logically, changing the logic with parport.0.xx.in-not is need be, testing the pin logic with hal and some hookup wire and slowly progressing through the process until the project is complete. This is something that I want to cover in my own cnc build and share with others that maybe it helps solidifies the concept for new comers. Kind of like I done with the video for installing LinuxCNC and the others.

Anyway, I am rambling, any input would be humbly accepted.

Joe

This value that I see, is it the actual logic value of the pin? In other words, If the value reads true, it would indicate that the pin is pulled up to 5V internally and if the value is False, the pin is pulled to ground internally? By internally, I mean by either the parallel port on the computer itself or the breakout board that is buffering it?

Probably too involved. The touch probe is a switch which is either closed or open. Very often probes are NC and break on contact.

The logic is seperate, you can manipulate it either way eg, when the probe contact breaks, an inverted pin produces HIGH instead of LOW.

Good idea though, can't have enough tutorials.

regards

ArcEye,

I agree that it is involved. What I am trying to do in the end, is give someone enough knowledge of how stuff works that it makes it easier to apply to another area. I don't know, maybe trying to explain the process on how to get from point A to point B may be more confusing to the new user.

Joe

Thanks Andy,

I thought it would be, just wanted to be like the valley boy and the two condoms, for sure, for sure.

Joe

JoeHildreth wrote:

ArcEye,

I agree that it is involved. What I am trying to do in the end, is give someone enough knowledge of how stuff works that it makes it easier to apply to another area. I don't know, maybe trying to explain the process on how to get from point A to point B may be more confusing to the new user.

Joe

I just meant that you now have to explain what pull-up and pull-down mean, a lot of peoples eyes just glaze over at terms like that

Your right about glazing eyes! I don't intend on giving a lesson in digital electronics. I phrased the question like that just to solidify it in my own mind.

In the tuturorials, I only want to explain that when working with a pin, halmeter will show you the value of the pin and that the value seen can be manipulated by using the -not at the end of the pin name. The other concept I want to push for them is what they need to bring out to use that pin in a switch circuit. If hal meter says the pin is false, then we need to bring a wire with 5V to complete the circuit, or a ground if it reads true. That sort of stuff.

A lot of the folks that I have dealt with coming into the CNC world are IT people or Metal Casters looking to expand their knowledge base. Most of them are not too familiar with (*)nix concepts. They think if there isn't a place in the GUI somewhere to set something up, then it is too hard. They don't grasp the power of LinuxCNC to be configured for just about any machine you can imagine, but too do so requires getting under the hood and tinkering with the innards a bit.

I guess what I am trying to say is the folks that say LinuxCNC is not as good as product X probably feel that way because there is no GUI to configure it. But in reality, those types of systems are crippling to the end user over the long haul.

Thanks ArcEye, as always I appreciate your feedback. God knows you have answered a bunch of questions for me over the last few years and given some perspective as well!

Joe