Easytherm is a tool that helps making curves from a few calibration points for an NTC temperature sensor.

Virtually noone uses easytherm nowadays to generate these curves.

The rest of this page is for experts who want to download manually, or generate their own custom files.

To make the process easier:

How to update calibration - using hexpatch.exe

hexpatch.exe was developed to help updating the vems.hex with the calibration tables

(hexpatch binary is also available on linux, or in sourcecode, but linux users rarely have problem with copypasting 32 lines)


command will change the airdenfactor _and_ matfactor for 3000,287 parameters. The output is named accordingly (instead of the generic vems.hex) for distinguisment in your storage. You can copy to vems.hex before uploading with upload_firmware.bat (or change the .bat to use the long-descriptively-named file).

changes coolant temp calibration in the file previosly patched (with the airX 3000_287 airdenfactor and matfactor tables). So coolant (thermfactor) can be changed independently (or left alone, if you like default coolant temp readings).

How to choose tables

Currently appr 56 example-tables are provided (28 airX + 28 clt), picking the best will closely match to almost any curve normally found in real life.

PTC - special type sensor with reverse slope (positive temperature coefficient: resistance, thus input voltage => ADC reading increases with temperature)

Audi 5cyl PTC (is this measurement of one of our members or from literature?)


vems.hex is distributed

with historical NTC calibration data (see 3050,256 file, it usually reads a bit high), though most will find 2063,256 a better match, as it will read (appr 7..9C) lower than a factory vems.hex

The coolant and manifold air temperature sensors are (in 99.9% of cases) NTC type. The ExhaustGasTemp sensor can never be an NTC type. [ATP Inc] has some useful notes about [NTC] and [PTC] sensors.


files are located in the files section of the Megasquirt group at http://groups.yahoo.com/ or directly from [msefi.com]


Propertherm - only for developers, see /svn/firmware/utilities/propertherm/