Support Contact probe with bed scanner eddy sensor

[markniu]

How does it work

1. probe:

The BDsensor can read the distance of bed to nozzle all the time. if the nozzle touch on the bed and the value of distance will stop changing, so we can use it as the triggered signal to printer.

2. z_offset adjust:

after triggered we move slowly up and down until the nozzle just leave the bed--->setting this position as the 0 position of z axis.

Requirements

This works with the bed scanner sensor BD_sensor,How to install bdsensor in marlin

Benefits

1. Auto z_offset calibration.
2. Overcome the temperature drift.

Configurations

1. enable BD_SENSOR, and add #define BD_SENSOR_CONTACT_PROBE in the configuration.h
   should like this:

#define BD_SENSOR
#if ENABLED(BD_SENSOR)
  #define BD_SENSOR_PROBE_NO_STOP // Probe bed without stopping at each probe point
  #define BD_SENSOR_CONTACT_PROBE // it uses nozzle collision sensing to probe while homing
#endif

2. Increase the speed of probe in the configuration.h,
   The sensitivity depends on the speed, so you need to adjust the speed of Z axis, the homing_speed and second_homing_speed should be in the range of 3 ~ 10, here is the z probe feedrate speed.
   for example:

 #define Z_PROBE_FEEDRATE_FAST  (5*60)
 #define Z_PROBE_FEEDRATE_SLOW  (5*60)

3. increase homing bump of z axis to > 4mm in the Configuration_adv.h

#define HOMING_BUMP_MM { 5, 5, 5 }

[thisiskeithb]

add #define BD_SENSOR_CONTACT_PRBOE in the configuration.h
should like

I imagine you meant BD_SENSOR_CONTACT_PROBE instead of BD_SENSOR_CONTACT_PRBOE.

Some comments that will improve the user experience a bit:

Add the option & disable by default (with typo correction) so the features is not hidden:

//#define BD_SENSOR
#if ENABLED(BD_SENSOR)
  //#define BD_SENSOR_PROBE_NO_STOP // Probe bed without stopping at each probe point
  //#define BD_SENSOR_CONTACT_PROBE
#endif

Increase the speed of probe in the configuration.h
The sensitivity depends on the speed, so you need to adjust the speed of Z axis, the homing_speed and second_homing_speed should be in the range of 2 ~ 5, here is the z probe feedrate speed.

This can be asserted at compile time if BD_SENSOR_CONTACT_PROBE is enabled.