Tunell 3D Printer Filament Monitor (Version 4)

$ 65.00 $ 72.00


3D Printer Filament Monitor

Find filament feeding faults before they ruin your print

We've all been there - a print job that ran out of filament just before the job finished; stuck filament because the spool was loaded incorrectly, a jammed hot-end due to accumulation in the nozzles - when these problems occur, we usually lose the job due to air-prints.

With the Tunell Filament Monitor, you can catch these filament feeding problems quickly so that you can fix the problem, instead of throwing the partial print away. For long-running prints, this indispensable upgrade will quickly pay for itself as it saves time and money lost to failed prints.

The Tunell Monitor uses a mechanical 24 PPR (positions-per-revolution) encoder to detect filament travel as you print.  If the filament has stopped moving for longer than the (adjustable) time-out period, a fault signal is sent to your printer.


  • Easy to use
  • Pauses your printer when filament feeding problem is detected
  • Easy connection to FlashForge Creator, Wanhao Duplicator 4, and MakerBot Replicator (original) using a 4-pin latching cable (included).
  • Successfully used with other machines: Ultimaker, Ultimaker 2, MakerBot Replicator 2, MakerBot Replicator 2X, RAMPS.
  • Supports dual-extruder systems (with the "Double monitor" option)
  • User-adjustable timeout for filament motion
  • Connection point for external pause button
  • Connection point for external alarm / relay / signaling LED
  • Current-limited output and reverse-voltage lockout circuit to guard against wiring mistakes.
  • Bypass mode operation to temporarily disable filament monitoring.
  • Ultra-Low Profile
  • Powered by Atmel mega168. Arduino programmable using a ISP hardware programmer (like  AVRISP mkII)
  • Version 4 - Latest version with design updates and improvements byToyBuilder Labs
  • Based on the original design by Aaron Tunell

About the Tunell Monitor, Version 4

ToyBuilder Labs manufactures and sells the latest Tunell Monitor (Version 4) in collaboration with the inventor of the original Tunell filament monitor, Aaron Tunell. (That's why it is called the Tunell Monitor, and not Tunnel Monitor!) The Tunell Monitor Version 4 electronics is a new design incorporating a number of updates over the original Tunell monitor, making this a hacker-friendly design for alternate uses:

1- Reverse polarity protection on the main power input.
2- Fault output pin can be configured as USART TX pin.
3- Secondary option signal can be configured as USART RX pin.
4- SPI lines on expansion port allow for easy hookup as SPI master or SPI slave in the future.  (For example, you can hook up a SPI LCD for adding a status display.)  The SPI lines also provides the 6-pin ISP connection for device programming.
5- I2C lines on expansion port allow for easy hookup as I2C master or I2C slave in the future.
6- Separate alarm drive pin that is an open-collector connection to ground. This allows hooking up a 12V buzzer or LED lamp, for example.
7- LED outputs tied to PWM output for hardware-dimmable R, G and B.
8- 4-pin Molex SL type G connector for easy attachment to Rep1 / FF / Wanhao Mightyboard and ToM-type Gen 4 electronics endstop receptacles.  Other end-stop and GPIO connections can be easily wired using common 0.100" pitch boxed jumpers.

Version 4 electronics

Tunell Monitor General Operations Guide

Click here for the Tunell Monitor V4 Operations Guide: Pdf



Printer-specific installation guide

Mounting Hardware
FlashForge Creator Pro Pdf No
FlashForge Creator Pro 2016 Pdf No

MakerBot Replicator (Original)
(Requires Sailfish Firmware)

Pdf D/L from Thingiverse No

Same basic steps as FlashForge Creator Pro

MakerBot Replicator 2
(Requires Sailfish Firmware)
Pdf   D/L from Thingiverse


MakerBot Replicator 2X
(Requires Sailfish Firmware)
Pdf   D/L from Thingiverse Yes
Ultimaker 2 (Marlin based)

Installation steps 


Required firmware [1]


See also Marlin and Others General Info

Fusion3 F306 (Marlin based) Pdf   D/L from Thingiverse No Contact manufacturer to ensure you have the right firmware for your specific printer. 
Marlin and Other General Info Pdf  

Preliminary implementation discussions. 


Github pull-reqeust (accepted) of bulge-sensor code changes to enable Tunell monitor.[2]

The bulge-sensor signal monitoring can be used with the Tunell monitor to detect filament outage.


[1]: Thanks to tinkergnome and gpb01 on the Ultimaker Forum

[2]: Thanks to Leon Grossman and Arthur Wolfman


Other Installation Information

  • For best results, securely mount the filament monitor to your printer.
  • Brackets for mounting the monitor to the MakerBot Replicator and Replicator 2, can be downloaded from Thingiverse
  • On some printers, you may need to solder a connection to use the monitor. See the connection documentation (below) on how to connect the monitor to your printer.
  • LATEST UPDATE: gpb01 on the Ultimaker forum, with help from tinkergnome, have successfully deployed the monitor on an Ultimaker 2.  See this post on the installation steps and this post on the enhanced firmware that made it possible to use the Tunell Monitor with the Ultimaker 2.


  • MakerBot Replicator 2, 2X, original Replicator, and Thing-O-Matics running the Sailfish firmware upgrade. (Sailfish Thingiverse Page.)
  • FlashForge Creator, Wanhao Duplicator, MBot, CTC, and other clones of the MakerBot Replicator with the Sailfish firmware.
  • Ultimaker 2 running the tinkergnome firmware for Ultimaker 2
  • Marlin-based printers with a available end-stop / expansion I/O-pin, running Marlin firmware with pause-support upgrade.
  • Other printer controllers that supports external pause signaling.


Important lead time notice

We are currently back-ordered on Tunell Monitors, as they are built and tested in small batches. Please allow a 1 to 6 week lead-time for your order to be filled.




Tunell 3D Printer Filament Monitor (Version 4) has a rating of 4.9 stars based on 11 reviews.

Are you ready to order? Or do you do you have a questions about our products? Maybe you are an educational institution and would like find out more about our discounts! What ever your concern, we are ready to listen and help! Here is how...


626 808 4010 M - F 9am - 7pm PST Lab Time:


ToyBuilder Labs Pasadena, CA


Need help right now? Take a look up there and click the Support tab!