[Idea/RFC] Automatic Sheet Detection for Legacy Printers (MK3S+/Mini) – NFC Tokens vs. Inductive Hacks  

[Idea/RFC] Automatic Sheet Detection for Legacy Printers (MK3S+/Mini) – NFC Tokens vs. Inductive Hacks

Hi everyone,

I’m sharing an idea born from frustration: I recently crashed my nozzle into the bed because I forgot to switch the sheet profile in the menu. I’m running legacy MK3S+ and Mini machines, so there is no loadcell/Nextruder magic here to save me.

While the MK4 and XL solve this automatically, there is a huge install base of older machines that could benefit from automation. I’ve been brainstorming two concepts to solve this: one involving new hardware (NFC), and one trying to exploit existing sensors (PINDA).

This isn't just about Z-offset; different sheets (like the new Cryo sheets) often require different bed temperatures or handling. Automating this would make switching materials much safer.

I’d love to hear your thoughts on the technical feasibility. Maybe this could be implemented in future updates or upgrade kits—if anyone from Prusa R&D is reading this: consider this a wishlist item from the community! 😉

Concept 1: The "Physical Key" (NFC / Open PrintTag)

The clean, robust solution.

With the development of NFC readers for the Prusa Mini (primarily for filament tracking / Open PrintTag), why not use this hardware for Sheet Management too?

The Problem with "Smart Sheets" (Tags on the Bed): Sticking an NFC tag directly onto a heated bed is difficult due to heat degradation (>60°C) and massive interference from the steel sheet itself. Furthermore, adding a sticker between the magnetic bed and the sheet adds local height, which could deform the bed or cause unevenness.

The Solution: "Swipe-to-Load" Tokens Instead of attaching the tag to the sheet, we use a generic Open PrintTag (keychain or card) configured as a "Sheet Token".

Setup: You assign a physical tag to your specific "Textured Sheet".

Workflow: Before inserting the sheet, you briefly swipe the tag past the printer’s NFC add-on (e.g., on the side of the display).

Action: The printer beeps, confirms the sheet ID, and instantly loads the correct HW-Profile.

The "Killer Feature": Portable Delta Z-Offsets We know that absolute Live-Z values are machine-specific (depending on how high the PINDA is mounted). However, we could store the Delta (Difference) on the tag.

The Logic: You calibrate your printer to a "Reference Standard" (e.g., Smooth PEI = 0).

The Tag Data: The tag for your Textured sheet stores: "I am 0.25mm thinner than reference."

The Result: Any printer reading this tag calculates: Current_Machine_Z + Tag_Delta. This would make sheet profiles truly portable between printers without recalibration!

Bonus: The printer could write "Print Hours" back to the tag, acting as a maintenance reminder for cleaning/refurbishing the PEI.

Concept 2: The "MacGyver Hack" (Inductive Coding)

The hardware-free solution using the existing PINDA/SuperPINDA.

If we don't want to add an NFC reader, could we modify the sheets so the PINDA sensor recognizes them?

The Physics Challenge: To create a readable binary code (like a crude EAN barcode) on the sheet handle, we need to modify the magnetic field.

Boosting the Signal: Adding Copper or Aluminum tape makes the sensor trigger earlier (higher).

Damping the Signal: Adding Ferrite foil or conductive polymers could shield the steel, making the sensor trigger later (lower) or not at all.

The Idea: We apply specific stickers to the handle area (outside the print zone). The printer probes 2-3 specific spots on the handle before printing.

Signal detected (High): "1"

Signal dampened/blocked (Low): "0"

Result: A binary code (01, 10, 11) distinguishing between Satin, Texture, and Smooth sheets.

The Obstacles:

Resolution: The PINDA sensor is quite large (8mm diameter). It acts as a trigger, not a high-res scanner. An actual "Barcode" is likely too fine, but 2-3 "Dots" could work.

Deformation: Even on the handle, thick stickers might prevent the sheet from sitting perfectly flat.

Flipping: Information is usually only on one side. If you flip the sheet to use the other side, the code is on the bottom and unreadable.

Discussion

I am curious about the community's and developers' take on this:

NFC: Would you use a "Physical Key" system to manage your sheets and prevent crashes? The idea of a "Portable Delta-Z" seems very powerful for print farms.

Inductive: Has anyone successfully used ferrite tape vs. copper tape to manipulate a PINDA sensor effectively?

Integration: Since the Open PrintTag hardware is already being explored for the Mini, could support for "Sheet Tags" be implemented in the firmware side-by-side with filament tags?

Let's bring some "Next-Gen" convenience to our trusty workhorses!

Happy printing!