probe problem

[kievari]

Hi,

First of all I am not sure if I posted this question of "probe" to the right place? If not I hope Administrators move it to the right category.

I am first time going to implement the "probe" technique. My machine is a 6040 one. I read tutorials and my understanding is that I have to connect an I/O pin of the printer port (where my printer cable connects my cnc control box) to a probing tool (that must be made) and define that pin in, say, Mach3 setting as the "probe pin". Next, to connect the common ground from the printer cable, to the, say, drill bit of the machine. Other part is the software which is not my question.

I thought that hacking printer cable (if it is needed at all) must not be the right way to do that. Googling shows that others seem to connect wires to the control box, not the printer cable as I first thought!

I opened my control box and I found even a "probe" hole-couple there, ready for the usage. The thing is that the probe on my board (as you can see on the image attached) is a + and -, not the printer cable pin (as a reserved one, as I expected), showing +4.9V typical.

Please help me to find out how I can implement the "probe" the right way, in my situation.

Thank you in advance.

[ger21]

Are you probing the surface of an object, or using the probe to set tool length?

[kievari]

Originally Posted by ger21 Are you probing the surface of an object, or using the probe to set tool length?

I was to learn the first, i.e. surface of object (mainly to start milling PCB for first time) and tool centering (or leading the tool exactly to a corner of an object, say a rectangle), the "set tool length" as a probing function is new to me. Would greatly appreciate if you please inform me of both.

[doorknob]

From the photo, the legend on the board says that the probe is connected to pin 13 of the LPT port.

It is possible that you are reading +4.9 volts on one pin of the two marked "probe" because that pin is "pulled high" through a "pull-up resistor" to the +5 volt power supply. If that is the case, then you should be able to short out that terminal to ground without damaging the board (and you should be able to detect that in your software by monitoring the state of pin 13).

If you want to verify that without risking damage to your board, you can try some experiments. For example, while monitoring that voltage with a multimeter, connect the terminal (that shows 4.9 volts) to ground through a 1,000 ohm resistor and see what that voltage changes to - if the pull-up resistor on the board is 1,000 ohms, you should see the voltage go down to 2.5 volts, or if the pull-up resistor is 4,700 ohms you should see the voltage go down to close to 1 volt, and so on, because you are making a resistor voltage divider.

The board is probably using a pull-up resistor on the probe line to make sure that when your software reads the signal on pin 13 of the LPT port, it will normally read a high signal except when the probe is touching ground, in which case it will read a low signal. In that case, you would set your software (for example, Mach3) to look for an "active low" probe signal.

The reason why the board has two pins for the probe is probably because they expect you to connect the probe to the board through a two-conductor cable, with one conductor connected to ground and the other conductor connected to the pin 13 probe input (at the board), and at the machine, the pin 13 connection wire is connected to a probe plate and the ground may be connected to a probe (or left unconnected if your probe is already reliably connected to ground). You could reverse the wires if the probe that you are using is not grounded, in which case the probe plate may be grounded.

[kievari]

Thank you for the detail explanation, I still feel confused and you know as this is working with voltage of the cnc controller (which in case of bad damage I have to wait for a month to get back from China), I'm going to be very accurate and before understanding well, not to do physical experiment!

Some questions:

>It is possible that you are reading +4.9 volts on one pin of the two marked "probe"
# how on "one" pin? I've tested with voltmeter this way: I guessed and connected the black wire of voltemeter to one probe pin, and the red wire to the other probe pin, so I'm reading this voltage between two probe pin not "on one pin". Please kindly tell me what you mean with "one probe pin"?


Next, there is nothing written under non of the pins about where to connect them (which one to pin 13 as you say, and which one to machine). By your post, I got this way that I have to connect the ground out of the two probe pins to the machine, and the other probe (positive +4.9v one) to pin 13, but should the connection pin of the pin13 be found on this board? If yes, then where please? I can't see it!

>...connect the terminal (that shows 4.9 volts) to ground through a 1,000
ohm resistor
You mean, the probe pin with +4.9 right? If so, then you mean simply shorting these two probe pins with a 1M ohm resistor and then measure them again, right?

{Here I'm totally confused}:
>The reason why the board has two pins for the probe is probably because they expect you to connect the probe to the board through a two-conductor cable, with one conductor connected to ground and the other conductor connected to the pin 13 probe input (at the board), and at the machine, the pin 13 connection wire is connected to a probe plate and the ground may be connected to a probe (or left unconnected if your probe is already reliably connected to ground). You could reverse the wires if the probe that you are using is not grounded, in which case the probe plate may be grounded.

Sorry for I'm not that fast to understand from first time, here I also fear to damage and that makes progress yet slower!

Edit:
If that is not too much to ask and if that won't take your time a lot, would you kindly give me a step by step to go and set the probe system for this machine please? I mean like 1.conncect ground to machine, 2...

[doorknob]

I am not able to answer in detail today, but maybe I will be able to do so tomorrow.

Do you have a friend who has electronics knowledge that can help you?

>It is possible that you are reading +4.9 volts on one pin of the two marked "probe"
# how on "one" pin? I've tested with voltmeter this way: I guessed and connected the black wire of voltemeter to one probe pin, and the red wire to the other probe pin, so I'm reading this voltage between two probe pin not "on one pin". Please kindly tell me what you mean with "one probe pin"?

Yes, that is what I meant - measuring the voltage on one probe pin compared with the other (or compared with ground).

Next, there is nothing written under non of the pins about where to connect them (which one to pin 13 as you say, and which one to machine). By your post, I got this way that I have to connect the ground out of the two probe pins to the machine, and the other probe (positive +4.9v one) to pin 13, but should the connection pin of the pin13 be found on this board? If yes, then where please? I can't see it!

If you look at the photograph that you attached to post #1, under the red and black wires at the lower left, it says "PROBE P13".

>...connect the terminal (that shows 4.9 volts) to ground through a 1,000
ohm resistor
You mean, the probe pin with +4.9 right? If so, then you mean simply shorting these two probe pins with a 1M ohm resistor and then measure them again, right?

I mean making a test by temporarily connecting those two probe pins with a 1K ohm resistor (1000 ohms) and then measuring the voltage again. Please report back the voltage measurement after you do that test.

[kievari]

Thank you, I'll do the 1Kohm test tomorrow and report the voltage. For now please let me still make sure with some points.

Do you have a friend who has electronics knowledge that can help you?
Theoretically yes, practically no, but I'm not that bad in electronics

If you look at the photograph that you attached to post #1, under the red and black wires at the lower left, it says "PROBE P13".
Yes that is right, but then where is the pin-hole for connection there? All what I see is a pin-configuration printed on the PCB, as if it is a "help" text. I expected that I can find a place to connect wire to pin 13, just like probe pins. But then that means I have to somewhat "hack" the printer cable connecting CNC controller and computer right?

I mean making a test by temporarily connecting those two probe pins with a 1K ohm resistor (1000 ohms) and then measuring the voltage again. Please report back the voltage measurement after you do that test.
Now understand, I'll do it this way (please tell me any comment needed):
1. I'll solder 2 pin-headers to the probes
2. extend them with wire down to a breadboard
3. insert the 1K resistor into the breadboard
4. attach 2 wires beside each side of the resistor
5. touch them with my multimeter set on voltage test.

I appreciate your help and support, thank you

[doorknob]

Originally Posted by kievari If you look at the photograph that you attached to post #1, under the red and black wires at the lower left, it says "PROBE P13". Yes that is right, but then where is the pin-hole for connection there? All what I see is a pin-configuration printed on the PCB, as if it is a "help" text. I expected that I can find a place to connect wire to pin 13, just like probe pins. But then that means I have to somewhat "hack" the printer cable connecting CNC controller and computer right?

My hypothesis is that one of the two probe pins (the one that measures +4.9 volts) connects to pin 13 (either directly or possibly through an optoisolator).

[kievari]

Originally Posted by doorknob My hypothesis is that one of the two probe pins (the one that measures +4.9 volts) connects to pin 13 (either directly or possibly through an optoisolator).

My question #1 is: method of "directly" connecting please? (no matter if probe is 13th or 15th pin)

Should I hack the cable? I won't solder to board, if there is no spec. header place for. Logically, cable is cheaper to replace than the board!

Or there is other method I don't know please?

[doorknob]

Originally Posted by kievari My question #1 is: method of "directly" connecting please? (no matter if probe is 13th or 15th pin) Should I hack the cable? I won't solder to board, if there is no spec. header place for. Logically, cable is cheaper to replace than the board! Or there is other method I don't know please?

I do not understand your question.

It should not be necessary to hack the cable. If pin 13 is connected directly to one of the two holes in the board labeled "probe", why wouldn't you connect the probe there?

[kievari]

Originally Posted by doorknob I do not understand your question. It should not be necessary to hack the cable. If pin 13 is connected directly to one of the two holes in the board labeled "probe", why wouldn't you connect the probe there?

So it means that where I have "probe pins", one of them is already = pin 13, the other is to connect to CNC machine, say, to the tool, right?

if so, why at all they put "two header holes"? If one is already connected to pin 13, nothing to do with it, I won't need that at all, right? I only need the one (ground) that is going to be connected to the tool, so why the hole is presented there at all, yet loaded with +4.9v?

I can't get the PCB creator logic in this!

[doorknob]

Originally Posted by kievari So it means that where I have "probe pins", one of them is already = pin 13, the other is to connect to CNC machine, say, to the tool, right? if so, why at all they put "two header holes"? If one is already connected to pin 13, nothing to do with it, I won't need that at all, right? I only need the one (ground) that is going to be connected to the tool, so why the hole is presented there at all, yet loaded with +4.9v? I can't get the PCB creator logic in this!

Almost.

The way that I think the board was designed is as follows:

1 - connect one end of a 2-wire cable to the "two header holes" (one wire to each header pin or header hole)

2 - bring the other end of that 2-wire cable to your machine

3 - my theory is that one of the wires from that cable (the one that measures +4.9 volts) probably is connected to pin 13 of the DB-25

4 - the other wire from that cable is probably connected to GND (at the board)

5 - so, at the machine, you can either:

a) connect the wire from pin 13 to a "z-axis touch plate" and connect the GND wire to your machine ground (spindle, tool, drill bit or whatever) which must also be connected to your metal probe

- or -

b) connect the wire from pin 13 to a z-axis probe (as long as the probe is not grounded!), and connect the GND wire to a z-axis touch plate

6 - set up your software so that the probe line, pin 13, is "active low"

7 - when the software tries to find the z-axis 0 coordinate, it should lower the probe until the probe makes contact with the z-axis touch plate. When the probe makes contact with the touch plate, the signal on pin 13 will change from +4.9 volts to 0 volts, and your software should see that as an "active low" signal.

So, that is how I think that it is supposed to work. Before testing that, though, I wanted to first test with the 1K ohm resistor to see whether my theory was correct (or to see whether my theory was supported).