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The FINDA sensor, sometimes referred to as F.I.N.D.A. is essentially the MK2/S PINDA sensor (without thermistor), upcycled to be used as a filament sensor. It is triggered by the proximity of the stainless steel ball. When the filament is pushed through the selector, it raises the ball towards the FINDA. There is a small red LED light on the top of the sensor that turns OFF when the filament is detected. When the filament is removed, the stainless steel ball falls back down and the red light turns ON.

The FINDA is not the same as the P.I.N.D.A. or SuperPINDA used on the MK2.5S and MK3/S/+ extruder. These are not interchangeable with the FINDA and it is important to differentiate the different Original Prusa induction sensors.

The FINDA sensor must be distanced correctly from the steel ball (blue ruler - left picture) so it is triggered only when filament is present (green arrow - right picture), pushing the steel ball higher.

FINDA height setup

The FINDA sensor has to be properly inserted into its socket: not too low, not too high. Check out our assembly manual, specifically this step, to see how the FINDA fits in.

  1. Supposing the steel ball and the FINDA are still in the selector, loosen the M3x10 screw holding the FINDA in place. Do not remove the screw, you just need to be able to move the FINDA up and down.
  2. Open the LCD menu -> Support -> Sensor info and focus on the FINDA value.
  3. Insert any 1.75 mm filament into the selector. The FINDA value should turn from 0 to 1.
    • If it does not change from 0 to 1, push the FINDA down a little bit. Keep in mind you must be able to move with the filament freely!
    • If it does change reliably from 0 to 1 as long as the filament is inserted, the calibration is done.
The tip of the sensor does not need to press directly on the steel ball in order to detect it, it is triggered by the magnetic field. Thus, do not press the FINDA down during step 3.

Finally, tighten the M3x10 screw to prevent the FINDA from moving. The steel ball, however, has to move freely!

FINDA troubleshooting

Debris in the selector

As explained in the first paragraph, the steel ball has to move freely. Sometimes, however, filament debris, dust, or strings may amass in the hole or even in the FINDA/ball socket. Use compressed air to clean it.

You can also use an interdental brush to clean debris. The diameter should be around 1.5 mm (0.06”) and the length should be 10-15 mm (0.4-0.6”)

Faulty sensor

You can always check the proper functioning of the sensor by inserting a piece of filament and observing the red light on top of the sensor. You can also go to the LCD Menu -> Support -> Sensor info to see the FINDA status. It should be 0 when the filament is out (red LED on) and 1 when the filament is inserted into the selector (red LED off).

In some situations, the FINDA itself may be working but its cable might be damaged and fail to transfer the information to the logic board. In most cases, it can be damaged during the assembly while doing cable management. It can be also damaged by opening the Idler body all the way and having it hang on the cables.

The best way to check the cable is to insert a piece of filament into the selector and go to the Sensor info menu. The FINDA value should be 1. Then wiggle with the cable and see if the value flickers and changes to 0 at any point.

Wiring

In case the FINDA value in the Sensor info menu is N/A during manual testing, check the cable connection to the MMU logic board and the MMU cable connection into the RAMBo board (MK3S / MK2.5S). Pay attention to the order of the colors of the individual wires. However, during load and unload, the FINDA value in the Sensor info menu will be N/A.