A very key aspect of the LIDAR compass is a live visual feedback system using a laser to point out all the positions where the structure is in-spec, so builders can make sure they lay bag in the right spot as they go. This visual feedback system requires a couple of key elements:

1. A (visible) laser to show where placement is correct
2. A means of turning that laser on and off while rotating it through the cross-section of the dome
3. Pursuant to (2), a means of measuring the LIDAR scan head position

(1, 2) are easy - lasers are cheap and low-power, so it should be no trouble to turn one on and off with just a microcontroller pin. Maybe a transistor, if that's not enough current. 

(3) is where the real fun lies: a reliable sensor to measure the scan head rotor position that we'll be piggybacking on, and code to handle that sensor appropriately. That's what this update is really about.

Putting the pieces together

The last LIDAR Compass update showed a proof-of-concept optical sensor that seemed to do a good job measuring a white dot on the edge of the rotor, and pulsing every time it went by. This update builds on that success, using that sensor and a physical assembly to build the entire chain, from figuring out where the scan head is in its rotation to pulsing the laser for set angular duration.