Connecting BL-Touch
===================

A **warning** before you start: Avoid touching the BL-Touch pin with
your bare fingers, since it is quite sensitive to finger grease. And
if you do touch it, be very gentle, in order to not bend or push
anything.

Hook up the BL-Touch "servo" connector to a `control_pin` according to
the BL-Touch documentation or your MCU documentation. Using the
original wiring, the yellow wire from the triple is the `control_pin`
and the white wire from the pair is the `sensor_pin`. You need to
configure these pins according to your wiring. For example:

```
[bltouch]
sensor_pin: P1.24
control_pin: P1.26
```

If the BL-Touch will be used to home the Z axis then set `endstop_pin:
probe:z_virtual_endstop` in the `[stepper_z]` config section and add a
`[homing_override]` config section to raise the z-axis, home the
x/y-axis, move to the center of the bed, and home the z-axis. For
example:

```
[homing_override]
gcode:
    G90 ; Use absolute position mode
    G1 Z10 ; Move up 10mm
    G28 X Y
    G1 X166 Y120 F6000 ; Change the X and Y coordinates to the center of your print bed
    G28 Z
set_position_z: 0.0
```

It's important that the initial Z upwards movement in the
homing_override is high enough that the probe doesn't hit anything
even if the probe pin happens to be in its lowest state.

Initial tests
=============

Before moving on, verify that the BL-Touch is mounted at the correct
height, the pin should be roughly 2 mm above the nozzle when retracted

When you turn on the printer, the BL-Touch probe should perform a
self-test and move the pin up and down a couple of times. Once the
self-test is completed, the pin should be retracted and the red LED on
the probe should be lit. If there are any errors, for example the
probe is flashing red or the pin is down instead of up, please turn
off the printer and check the wiring and configuration.

If the above is looking good, it's time to test that the probe
responds to commands from the firmware. First run `BLTOUCH_DEBUG
COMMAND=pin_down` in your printer terminal. Verify that the pin moves
down, and that the red LED on the probe turns off. If not, check your
wiring and configuration again. Next issue a `BLTOUCH_DEBUG
COMMAND=pin_up`, verify that the pin moves up, and that the red light
turns on again. If it's flashing then there's some problem.

Now, it's time to test homing with a twist. Instead of letting the
probe pin touch the print bed, let it touch the nail on your
finger. So issue a `G28`, wait until it starts to move down, and stop
the movement by very gently touching the pin with your nail. You
probably have to do it twice, since the default configuration makes it
probe twice. But be prepared to turn off the printer, to avoid damage,
if it doesn't stop when you touch the pin.

If that was successful, do another `G28` but this time let it touch
the bed as it should.

Calibrating the BL-Touch offsets
================================

Follow the directions in the [Probe Calibrate](Probe_Calibrate.md)
guide to set the x_offset, y_offset, and z_offset config parameters.

It's a good idea to verify that the Z offset is close to 1mm. If not,
then you probably want to move the probe up or down to fix this. You
want it to trigger well before the nozzle hits the bed, so that
possible stuck filament or a warped bed doesn't affect any probing
action. But at the same time, you want the retracted position to be as
far above the nozzle as possible to avoid it touching printed parts.
If an adjustment is made to the probe position, then rerun the probe
calibration steps.

BL-Touch gone bad
=================

Once the BL-Touch is in inconsistent state, it starts blinking
red. You can force it to leave that state by issuing:

 BLTOUCH_DEBUG COMMAND=reset

This may happen if its calibration is interrupted by the probe being
blocked from being extracted.

However, the BL-Touch may also not be able to calibrate itself
anymore. This happens if the screw on its top is in the wrong position
or the magnetic core inside the probe pin has moved. If it has moved
up so that it sticks to the screw, it may not be able to lower its pin
anymore. With this behavior you need to open the screw and use a
ball-point pen to push it gently back into place. Re-Insert the pin
into the BL-Touch so that it falls into the extracted
position. Carefully readjust the headless screw into place. You need
to find the right position so it is able to lower and raise the pin
and the red light turns on and of. Use the `reset`, `pin_up` and
`pin_down` commands to achieve this.
