obligatory obscure reference

self-deprecating yet still self-promotional witty comment


ThermistorTable for 1mm thermistors

Filed under: MakerBot — jet @ 13:23

Before you assemble your extruder, check to see how big the thermistor head is. If it’s around 1mm and not around 3mm, then you might want to use a different set of values in the thermistor lookup table, as the resistance is different at various temperatures.

The reason this matters is that it’s how the Cupcake monitors the temperature of the extruder. You want to be printing ABS at around 220C, but the smaller thermistor will “read low”, so the temperature reported back to the software is off. To get to the right temp, you have to fudge it and set it at 240, then make sure you change it to 240 anywhere in g code generated by software.

It’s easier, in my opinion, to just make/use a new ThermistorTable.cpp:

  1. if you have access to a temperature probe that’s good up to around 260C, use the reprap thermistor page as a guide to making your own table.
  2. follow the makerbot wiki instructions on upgrading your firmware to verify that the default software will build/install. If anything goes wrong, or this table doesn’t work for you, you need to be able to revert.
  3. make a backup of the ThermistorTable.cpp file
  4. copy the new table (found below) into ThermistorTable.cpp
  5. rebuild and install just like you did with the default software

This is the table I’m using with a 1mm thermistor, I’m able to set the temp to 220C and print quite nicely.

#include "ThermistorTable.h"
// Thermistor
 lookup table for RepRap Temperature Sensor Boards (http://make.rrrf.org/ts)
// Made with createTemperatureLookup.py (http://svn.reprap.org/trunk/reprap/firmware/Arduino/utilities/createTemperatureLookup.py)
// ./createTemperatureLookup.py --r0=93700 --t0=24 --r1=0 --r2=4700 --beta=4881 --max-adc=1023
// r0: 93700
// t0: 24
// r1: 0
// r2: 4700
// beta: 4881
// max adc: 1023
#define NUMTEMPS 20
short temptable[NUMTEMPS][2] = {
   {1, 477},
   {54, 189},
   {107, 159},
   {160, 142},
   {213, 130},
   {266, 120},
   {319, 112},
   {372, 106},
   {425, 99},
   {478, 93},
   {531, 88},
   {584, 82},
   {637, 77},
   {690, 71},
   {743, 65},
   {796, 59},
   {849, 51},
   {902, 43},
   {955, 30},
   {1008, 4}

1 Comment »

  1. Thanks for this, I was having the same issue and this lookup table is exactly what I needed.

    Comment by Jeff — 2010/06/09 @ 10:00

RSS feed for comments on this post.

Leave a comment

Powered by WordPress