BLTouch is a simple-to-use bed probe from the folks at ANTCLabs. It's simple because it senses and moves a probe-pin with an electromagnet, which gives it a very small footprint and makes it easy to mount onto different printers. You can find out more on the IndieGoGo page
BLTouch is a bit harder to set up in software because it pretends to be both an endstop and a servo. The servo interface is used to deploy and retract the pin, and the endstop interface conveys when the pin hits the bed. The endstop interface is also a bit tricky because it isn't persistent - the pin triggers, the endstop sends a 5ms pulse, then the device resets.
Use with Redeem
It is currently recommended to use the BLTouch with the develop branch of Redeem because the new PRU firmware therein is much more tolerant of the short pulse-time of the BLTouch. Either way, though, your BLTouch needs to be connected to an endstop input of your choice and the X2 or Y2 pins for the servo half. See Redeem#Servos to learn more about that.
On Replicape/Redeem, BLTouch is support for probing but not homing because it only sends pulses. Homing is theoretically possible but currently not implemented - feel free to file an issue at the issue tracker if this is something you could use.
Assuming you plug the servo input into X2 (being careful to match up the data/ground/5v pins according to Replicape_rev_B#Fritzing_example ), your servo config should look like this:
[Servos] servo_0_enable = True servo_0_channel = P9_14 servo_0_angle_init = 90 servo_0_angle_min = 0 servo_0_angle_max = 180 servo_0_pulse_min = 0.0006 servo_0_pulse_max = 0.0024
Make sure to also add an appropriate endstop config. On a delta where the BLTouch's endstop half is connected to Z2, that would look like this:
[Endstops] end_stop_z2_stops = x_neg, y_neg, z_neg
A cartesian only needs to block the Z axis like this:
[Endstops] end_stop_z2_stops = z_neg