This is the recently-concluded story of my printrbot's trip to manual bed leveling land and back again.

Above is a picture of the custom printer hot-plate I made while pursuing serialized printing. Before this my print bed had been aluminum, and worked with my printrbot's stock inductive leveling probe. Now the z-probe couldn't "see" any metal through that plate of borosilicate glass. What was I to do?

Well, first I put some copper tape on the glass (shown above) where common points for using the inductive probe were. That didn't give very good results though, so I decided to try and find a way to increase the operating distance of my sensor.. And how do you do that? By increasing the voltage to the sensor! It safely accepts 6-36V input, and I just assumed that it stepped down the signal output line to some 3-5V logic.

I assumed wrong. Highlighted in the image above is the fried mosfet which was used to step the z-probe signal line down to 5V logic for the microcontroller. When I ramped up the sensor's power voltage, the signal line followed, and blew out that component.

But I was in luck! I had just taken an EE course on transistors. With my newfound ability to sketch out an NPN circuit, I wired in a 5V tolerant replacement.

And I wound up just buying a beefier sensor to detect metal through the glass print bed:

This would have been a success, except the replacement sensor wasn't all that precise and I eventually gave up on it. I then removed the sensor entirely and put the print bed up on springs, leaving me to manually level the bed. This worked great, because I could really finely control the adjustment and get the first layer height really tuned in.

Fast forward to this summer. I realize that I've started having to re-level the bed between every print. The z-axis loses some steps somewhere after every print, and always returns to ~0.5mm instead of 0.0mm. It's starting to get old, so I decide the time is neigh for reinstalling a z-probe and returning the printer to auto leveling.

Guess what I did? Yup, I forgot about the delicate replacement transistor and I threw on the old high-voltage sensor which promptly fried the transistor. Crap, now what?

After more time than I care to admit, it dawned on me that as I went back to using a 5V sensor, scrounging up a replacement transistor shouldn't be necessary. The ATmega runs at 5V. The sensor runs at 5V now. They should be able to interface directly.

So that's what I did: just bridged the sensor line over to the microcontroller and pray the board schematic I found online was accurate.

It worked! The printer is back to printing, and I didn't have to go order a transistor online!

That's all, folks!