Touch probe inquiry

#1

Hello,

I have a pocket nc v2-10 with the latest kinetic control (just upgraded last weekend (10/24/25)).

I saw Josh Pieper tutorial on his touch probe and got excited to add one. I noticed that he had to create a splitter (I haven’t gone through his whole project yet) and was wondering if there was a cleaner method. It seems like the staff was ok with this (I did see the warning about the limit switch effecting the calibration) so I wanted to ask if they could provide clarification on a way to access a pin for this probe input.

I have been learning about Linux cnc a little and see that it uses a parallel port (and a breakout board) from what I saw on my pocket nc that seems to be the hat the beagle board is connected to. Is there a way to pull out a connector from there and keep it close to the current inputs (Ethernet/usb) on the front? I was wondering if the electrical schematic is available too.

I am a noob at cnc and have some software and electrical experience so will prob get some of this wrong as I learn about it!

Thanks for your input here.
Guy

Oh one more thing, I read on another post that kinetic control has to support the probe inputs too. I think it was working a little (z axis?) but might run into issues with this later.

11/2/25 update
I took a pic of the BBB and daughter board. This showed me the free pins (assuming they are actually free!). P9 GPIO_20 (pin 41) looks free (would love some verification here ;)).

I bought a BBB and made an image of the sd card to run it with. I have the Kinetic control working but it looks like halcmd is failing since there is no hardware to talk to (again assuming since I don’t know this side of things :()

free pins
free pins1684×749 363 KB

11/3/25 update

***Work in Progress Use at Own Risk***

Guide to Adding a Stock Probe to PocketNC on Pin P9_41

This guide provides a clear, step-by-step process to add a stock probe to your PocketNC on pin P9_41 (STOCK_PROBE_PIN=941), integrating it with LinuxCNC and ensuring proper signal inversion for an active-high probe. The process involves physically connecting the probe, configuring the INI and HAL files, and creating a G-code subroutine for probing. Tested as of November 3, 2025, 11:49 PM EST.

Prerequisites

  • PocketNC running LinuxCNC with Pentamachine’s Kenetics interface.
  • A stock probe (active-high, TRUE when triggered) with a 5V to 3.3V level converter.
  • Administrative access to run sudo commands (pocketnc user has this).

Step-by-Step Instructions

1. Physically Connect the Stock Probe

Connect the stock probe to the BeagleBone Black:

  • Hardware Setup:
    • Attach the probe’s signal line to GPIO_20 (pin 41, P9_41) on the BeagleBone Black.
      • I did this by using breadboard wire
    • Use a 5V to 3.3V level converter to ensure compatibility with the BeagleBone’s 3.3V logic.
    • Connect the probe’s power and ground lines as per its specifications (typically 5V power, ground to BeagleBone GND).
  • Verification: Ensure the probe outputs a 3.3V signal (from level converter) when triggered (test with a multimeter if needed).
  • Images:
    image1
    image1480×640 118 KB

    Pin 41 for probe signal and Pin 43/45 for ground

image0
image0480×640 120 KB

currently testing with a 5v/3.3v breadboard powersupply and a voltage converter to input 3.3v to beaglebone board (I assume everyone knows 5v will fry it!!!)

2. Overcome Read-Only Filesystem Access to update/generate files

The /usr filesystem (containing /opt/pocketnc/) may be read-only due to OSTree. Temporarily bind it to a writable location:

sudo mkdir -p /tmp/settings
sudo mount --bind /usr/opt/settings /tmp/settings
sudo mount -o remount,rw /tmp/settings

Once done with the file editing, clean up the mount (or reboot)

sudo umount /tmp/settings
  • Note: This is a working solution to the filesystem configuration. I am not sure if there is better ways to do this (both mounting to gain access and unmounting/reboot afterwards). Please advise!

3. Add STOCK_PROBE_PIN to Base INI

Ensure the pin is defined in the configuration:

sudo nano /opt/pocketnc/Settings/versions/v2revR/PocketNC.ini
  • Modify: Add to [POCKETNC_PINS] section (below the INTERLOCK_OPEN_PIN):
STOCK_PROBE_PIN=941
  • Save: Ctrl+O, Enter, Ctrl+X.
  • Purpose: Defines pin 941 for the stock probe.

4. Create v2_stock_probe Feature Files

Set up the HAL file, HAL inclusion, and signal mapping:

sudo mkdir -p /opt/pocketnc/Settings/features/v2_stock_probe
sudo nano /opt/pocketnc/Settings/features/v2_stock_probe/v2_stock_probe.hal
  • Content for v2_stock_probe.hal:
    # Stock Probe - ball is 0.0780"/1.98mm
newinst bb_gpio stock-probe-pin pin=[POCKETNC_PINS]STOCK_PROBE_PIN direction=input
setp stock-probe-pin.invert 1
unlinkp probe-inputs.in-2
net probe-input-0 probe-inputs.in-2
  • Save: Ctrl+O, Enter, Ctrl+X.
sudo nano /opt/pocketnc/Settings/features/v2_stock_probe/append.inc
  • Content:
    [HAL]
HALFILE=/opt/pocketnc/Settings/features/v2_stock_probe/v2_stock_probe.hal
  • Save: Ctrl+O, Enter, Ctrl+X.
sudo nano /opt/pocketnc/Settings/features/v2_stock_probe/overlay.inc
  • Content:
    [PENTA]
STOCK_PROBE_SIG=probe-input-0
  • Save: Ctrl+O, Enter, Ctrl+X.
sudo chown pocketnc:pocketnc /opt/pocketnc/Settings/features/v2_stock_probe/*
sudo chmod 644 /opt/pocketnc/Settings/features/v2_stock_probe/*
  • Purpose: Configures pin 941 as stock-probe-pin, inverts the signal, and maps it to probe-input-0.

5. Enable Feature in Base INI 

sudo nano /opt/pocketnc/Settings/versions/v2revR/PocketNC.ini
  • Modify: Add to [PENTA_FEATURES] section:
    V2_STOCK_PROBE=1
  • Save: Ctrl+O, Enter, Ctrl+X.
  • Purpose: Instructs generateINI.py to include v2_stock_probe.hal.

6. Restart services

Use the Kinetic Control UI - Config → Machine Config: Restart Services button

  • Purpose: Regenerates /var/opt/pocketnc/PocketNC.ini and reloads LinuxCNC.

7. Verify Pin and Signal 

halcmd show pin motion.probe-input
halcmd show sig | grep probe

Example sig output:
Probe NOT triggered

bit FALSE -- probe-input
                                 ==> motion.probe-input
                                 <== probe-inputs.out
bit FALSE -- probe-input-0
                                 ==> probe-inputs.in-2
                                 <== stock-probe-pin.in

With probe triggered

bit TRUE -- probe-input
                                 ==> motion.probe-input
                                 <== probe-inputs.out
bit TRUE -- probe-input-0
                                 ==> probe-inputs.in-2
                                 <== stock-probe-pin.in
  • Expected Output:
    • Pin: bit OUT FALSE stock-probe-pin.in (open) or TRUE (triggered).
    • Signal: bit FALSE probe-input-0 (open) or TRUE (triggered).
  • Purpose: Confirms pin 941 is active and toggles correctly.

8. Create G-Code Subroutine - ***Need to polish this. May work or may not depending on current coordinates…

echo -e "O<stock_probe> sub\nG91\nG38.2 Z-3 F5\n#<probe_z> = #5063\nG90\nG0 Z[#<probe_z> + 2]\nM2\nO<stock_probe> endsub" > /home/pocketnc/stock_probe.ngc
  • Purpose: Defines a subroutine to probe down, store the Z position, and retract.

9. Integrate Subroutine with Kenetics

To be tested and finalized. The G-code stock_probe.ngc must be added to Kenetics’ subroutine library:

  • Placeholder Steps:
    1. Copy /home/pocketnc/stock_probe.ngc to the Kenetics subroutine directory (e.g., /home/pocketnc/subroutines/ or /usr/opt/settings/subroutines, confirm path).
    2. Register the subroutine in Kenetics - subroutine can be called from web interface o<stock_probe> call (this may be enough?)
    3. Position the probe with enough room and have the probe in your hand to manually test.
  • Expected Behavior: Z-axis moves to the left, when probe triggers it stops, and retracts.

10. Verify G-Code File 

ls -l /home/pocketnc/stock_probe.ngc
  • Expected Output: -rw-r--r-- ... stock_probe.ngc.
  • Purpose: Confirms the G-code file exists.

Testing and Troubleshooting

  • Verify Files:
    ls -l /opt/pocketnc/Settings/features/v2_stock_probe/
    Expect: -rw-r--r-- pocketnc pocketnc for all files.
  • Check INI:
    grep STOCK_PROBE_SIG /var/opt/pocketnc/PocketNC.ini
    Expect: STOCK_PROBE_SIG=probe-input-0.
  • Debug Signal:
    halcmd show all | grep -E "stock-probe|probe-input-0"
    Look for: stock-probe-pin.in → stock-probe-raw → stock-probe-oneshot-or.out → probe-input-0.

This guide ensures a replicable process for adding a stock probe and manually testing. Probe routines and perhaps a script to automate the setup to come!

Update 11/6/25:
Pics and hopefully usable tutorial

Todo:

  1. Getting parts to house an external setup (pins unfortunately still need to be connected to board in some way).
  2. Pull power from BBB and internalize components (provide a usb C (non-standard) to the side wall of the cover and make a usb c connector for the probe to cleanly connect to machine (5v and 3.3v!) during probing (no external powersupply needed!)

image3
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If interested this was the trigger time for probe (~7.6 us)


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#2

Really nice write up and details for others if they are feeling brave. Please update as you evolve this solution. Out of interest, how is the repeatability of the touch probe? I have a probe but it’s still in the box. Was planning to have it as a dumb light only for setting but now I have an accurate self centering vice solution I haven’t had much use for a probe.
Cheers
TP

#3

Thanks! I haven’t tried testing the repeatability yet. I am making an external closure for the signal to converter box but need to get my 3d printer working first then I can test the repeatability next. The specs say repeatability accuracy: 0.01 mm/ 0.0004 but we will see :slight_smile: (oh I am using this probe from amazon. It was 6mm shank so that fit perfectly into my collet :smiley:

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