How to connect the 2nd thermistor?

Since the above question came up several times, here some more details on this:

To connect a thermistor to one of the free analog pins of the extruder controller v2.2’s Arduino chip, besides the thermistor itself, two additional electronic parts are needed:

  • 100k Thermistor (e.g. from here)
  • 4.7kΩ Resistor
  • 10µF Capacitor

Here’s the schematic:

Schaltplan 2nd Thermistor

I soldered the resistor and capacitor directly onto a connector:

IMG_4424 IMG_4425

This “adapter” is then connected to the -then- unused analog pin 6 on the extruder board:

[Update 03/21/10: Just to clarify: YES, the red labels in the diagram below are correct! The labels in the board’s silk screen are wrong!]



That’s it for the hardware side.

To handle the new input on the software side, the firmware of the extruder controller needs an update.

See my last post for more information on this. There’s a patch for the board firmware itself and one for ReplicatorG (for visual feedback and to enter a target temperature).

All these changes are also part of the next firmware/Replicator G release. All the sources are available through MakerBot’s public GIT repositories at

Schematics based on


  1. Hey,
    please help me short. I want to build the heated platform like you.
    Ok, but I have the following problem: You get two wires form the heated platform, don’t you? And two extra wires for the thermistor, as seen too. But why you are writing about four wires for the heated platform on A-A+?

    • When heating at full power, there are about 2A current on these lines. Since the wires I use are quite thin, I connected two of them in parallel for each line on A+/A-. Not sure if this is necessary, but I wanted to avoid melted insulations on that cable…

  2. Zaggo, are the GND and A6 pin labels switched in the extruder board diagram above? I think I see a different pinout described in the RepRap wiki.

  3. renerage, the silk screen on the board contains an error. The pins marked as “+” are really “A6” resp. “A7”, the pins marked as “-” are “VCC” and the pins marked as “A6″/”A7” are connected to GND. That’s why I drew the diagram with the red markers above :)
    I guess it’d be a good idea to clarify this above…

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