MMU2s IR Sensor Status Indicator

It is useful to be able to see at a glance if the IR filament sensor detects filament. You can get this information by scrolling through the LCD menus, but this mod gives instant visual feedback. Their are some other similar mods published, but this one

1. Doesn't alter the stock IR Sensor board eg no parts to solder on to it.
2. Plugs in series to the existing board and is easy to install and remove. It simply goes in series between the existing board and cable.
3. Uses easily obtainable non-SMD parts.

BOM:

• A 3 pin pass through (stacking) female header (like on an Arduino shield)
• 13mm x 7.5mm stripboard
• 100ohm ¼ watt resistor
• 1200ohm ¼ watt resistor (560ohm if a low efficiency LED is used)
• 5mm green TTH LED (I used a high efficiency one)
• 2N7000 N channel MOSFET

Wiring is as per the circuit diagram. The female header plugs into the IR sensor board, and the cable from the Einsy board plugs into the male end of the passthrough.

The LED is driven by the MOSFET, which also acts a NOT gate. The middle pin from the sensor goes logic high when there is no filament, and logic low when filament pushes on the idler. Because the MOSFET gate draws almost no current, it avoids potentially interfering with the signal from the sensor to the ADC pin on the Einsy processor. This has been tested only on the most recent version of the IR board.

The conductor strip needs to be drilled away between the ends of each of the resistors. This is shown in the photographs. Correct polarity and orientation are important for the LED and the MOSFET.

The printed cover is a replacement for the MMU2s “chimney” cover. It needs to be printed with the down-side on the print bed, which means supports are necessary. I printed the part in Prusament Jet Black PETG, with the support interface layers in PLA, which peels off the PETG nicely, but standard supports with PETG should also work.

Disclaimer: If you decide to implement this modification, it is solely at your own risk. Incorrect wiring can damage your printer, and potentially cause other serious consequences like electrocution or fire. You should not attempt to do any electrical work without  appropriate knowledge, training or experience.