Since it’s a wheatstone bridge with all four legs sensing (two resistors on top of PCB compressing, two resistors on bottom stretching) and what’s being measured is just a change in relative resistance, it should be very sensitive even if one of the resistors is misaligned.
@Ryan_Carlyle even still, if the same could be done using the pcb trace instead of a resistor, it could be preferable. I am willing to try both. It seems like a very inexpensive and potentially accurate system.
@Griffin_Paquette Duet3D is already doing this with their SmartEffector. The problem is that the meandering trace takes up a LOT of board space.
(btw, the Smart Effector is open source GPL3 if you want to use it. I will be!)
I understand how this thing works now at a theoretical level. I think I’m gonna use some large-package TFRs on a modification of the smart effector to make a half-bridge version that takes up less board space.
You could do 0.5oz copper or 4 layer.
@Stephanie_A SeeMeCNC has an end effector that I think they’re doing that on - they even state that it’s based on the Duet3D Smart Effector, but I have not been able to find the sources for their PCB anywhere.
By the way, there’s no intrinsic reason why this has to be on a special hot end mount. You could build this kind of force sensing into, say, a bed PCB heater. Say little tab-wings that stick off the side near the mounting points.
@ThantiK I had one and it was complete shit. We had to have ours replaced and it still didn’t work. I am just realizing now that it was this style.
I can look around for it if it would be of any use.
@Griffin_Paquette You don’t want yours? - lol, I’d love to take it off your hands if you have no use for it. I’d like to experiment with the wheatstone bridge for personal use.
Especially if you have the blue heatsink that goes with it, I’ve got a shitty setup on mine that I can probably make it work with if I put a larger excitation voltage on the bridge.
Fascinatingly innovative. I 
this thread. Stuff like this is what I’m going to miss most when G+ goes down.
this is really interesting
@ThantiK I messed with it before and couldn’t figure out what was wrong with it. Had some ground short somewhere. The replacement had the same issue
I wonder how much force is necessary to sense a touch. Maybe I should read the linked article… The main thing I don’t like about probing with the extruder is the nozzle needs to be clean, with zero frozen ooze. Or, if the nozzle is hot, you can’t probe a part of the bed with PEI, BuildTak, etc. on it. Still, a clever idea if you want to probe with the nozzle.
You guys should check these out 
https://www.ebay.com/p/5pcs-Bf350-3aa-Bf350-350-Ohm-High-precision-Pressure-Resistance-Strain-Gauge-Set/769200641?iid=323087798934&chn=ps
@Shai_Schechter I have. They’re difficult to install correctly. I was playing with them back in 2015 or so, but my boss wasn’t interested and I didn’t have the requisite knowledge to make them function.