docs: Bltouch documentation (#1073)

Add documentation on howto configure the BL-Touch device with
Klipper. A second paragraph addresses possible issues with BL-Touches

Signed-off-by: Wilfried Goesgens <dothebart@citadel.org>

1 files changed, 64 insertions, 0 deletions

diff --git a/docs/BLTouch.md b/docs/BLTouch.md
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+Connecting BL-Touch
+===================
+Once you've hooked up the BL-Touch servo connector to a `control_pin` according to the BL-Touch
+documentation or of your MCU. Using the original wiring, the yellow wire from the tripple is
+the `control_pin`, the white wire from the pair is the `sensor_pin`. You need to configure
+these pins according to your wiring with Klipper:
+
+    [bltouch]
+    sensor_pin: P1.24
+    #   Pin connected to the BL-Touch sensor pin. This parameter must be
+    #   provided.
+    control_pin: P1.26
+
+Calibrating the BL-Touch
+========================
+
+### Z Offset
+In order to make klipper work properly you need to tell it in which relation to the nozzle
+the probe is exactly located. Lets start with the `z_offset` - the height of the probe when
+its expanded:
+
+Make sure the probe is above the bed by moving the head into an appropriate x/y position:
+
+    g0 x0 y0
+
+Now make klipper aproach the bed until the probe triggers using:
+
+    PROBE
+
+This should deploy the BL-Touch probe, stop the run when it triggers by touching the bed.
+Now acquire the current position from the reached `z_offset` using:
+
+    GET_POSITION
+
+In the output lines the `toolhead` line with the `Z:` contains the required value.
+
+### X/Y Offset
+In order to find the propper vertical offset of the probe you need to know a certain point of
+your bed. X/Y = 0 may be a good point for this, any other will do as long as you know it.
+Find it by lowering the nozzle next to it using `g0 z0.5`. Create a removeable mark on your
+bed by i.e. using a non permanent marker.
+
+Now move the tip of the BL-Touch over that point by jogging there with the conrols in the `control` tab of
+OctoPrint. Once the BL-Touch is roughly over the point acquire it using the `GET_POSITION` command.
+The difference to your marked point is your `x_offset` and `y_offset` to configure in the `printer.cfg`.
+
+
+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 happenes if the
+screw on its top is in the wrong position, or the magnetic core inside the probe pin has moved.
+If its moved that way up that it sticks to the screw, it may not be able to lower its pin anymore.
+With this behaviour you need to open the screw, pick i.e. a ball-pen and push it gently back in place.
+Re-Insert the pin into the BL-Touch so that it falls into 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.