Just saw the schematic. It is indeed a bridge. Looks like 2 branches are made with I suppose, 3 tracks each, the other 10k ref R. Op amp direct to the ADC. All signal treatment done by software. Much more sophisticated and versatile than the Piezo system where it is done via OP amp and comparator. Really neat.
"You failed to maintain your weapon, son" (Harry Brown )
The firmware is also published now, see [duet3d.com] for the link.
The hardware is indeed a bridge. The 3 sensor areas on each side are connected in series. The electronics and firmware looks for changes in the bridge output in a limited speed range, so that slow changes due to e.g. the underside heating faster than the top side don't trigger it.
Delta printer calibration calculator, mini IR Z probe, and colour touch screen control panel: [escher3d.com]
Do you have any information how the Smart Effector would perform in a heated chamber (say 50-60C). I really like the idea and design, but I am not sure if it is allowed to be used in a heated environment...