It’s so simple a problem that it’s a giant pain in the neck! To further automate the microscope, I need a way for the program to find a “home” position — a starting point. Something that won’t strip gears, crack slides, or otherwise cause mayhem.

Most X/Y/Z devices (3D printers, laser cutters, CNC routers, etc) use limit switches. The trouble is the way the microscope stage moves.

X – Moves just the slide left/right
Y – Moves the stage forward/back
Z – Moves the entire stage up/down

So, you either start attaching switches in weird places (on the stage, on the body) or come up with something else. Added fun? The top limit of Z should change depending on the objective lens. And, by the way, not the entire stage moves for Y — just the very top of it. But, Z does move everything. You start to see my problem.

How to cleanly find home, inexpensively, with as little modification to the microscope as possible?

I’ve looks at more sensors than I wish to admit:

Time of Flight (Laser) — Good for finding a single direction of movement, but I’d need three at $15 each. I tried some ideas of using just one for X and Y, but that didn’t pan out.

RGB Sensor Through Eyepiece — Find the “dark” / black and you determine the edges of the sample. Works fine, in a controlled (dark) environment, but reflected light (from the room light, bouncing off the top of the slide) messes with the readings.

Hall Effect Sensors — Like switches, but triggered by magnets. Most promising, but when Z is moved, their point of triggering changes. I pretty much need a constant/known distance between magnet and sensor.

Accelerometer / Magnetometer — AKA Gyroscope and Compass — Good for finding Yaw/Pitch/Roll, but since the microscope doesn’t Yaw/Pitch/Roll, not helpful for me. The stage movements are too small to accurately tell if its moving in a particular direction. Perhaps this is a solution, but I’ve not figured out how to tease out good data.

I was also thinking of a proximity sensor, like the one found on our Prusa 3D printer. Kinda like a Hall Effect without the magnets. But, the sensors aren’t cheap ($15-$30 each), pretty big, and I’d need three. And the whole range of motion problems and where to mount them.

So, for now, I’ve admitted defeat and gone back to micro switches. I’m hoping to get them working “good enough” so that I can write code. For now, the focus (ha-ha) is on X and Y. I’ll add Z later. (Z is less important, as the focus really needs a human eye, or smart AI.)