Temperature (ADC) Calibration

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DC42
1. I have added optional parameters L and H to the M301 (set hot end PID parameters) and M304 (set bed PID parameters) commands. These allow the offset and gain errors inherent in the SAM3X ADC to be corrected. The values you set are stored to flash memory, so they survive power down cycles and resets, but not re-flashing the firmware (which sets both values to zero). You can use positive or negative values, integer or fractional. The H parameter affects mostly the low-temperature readout, and the L parameter affects mostly the high-temperature readout. To determine the correct values for your Duet board:

(a) Simple method: with the hot end at room temperature and a thermometer to tell you the temperature, send command M301 Hnn for various values of nn until you discover the value of nn that gives the correct temperature readout. Do not set the L parameter.

(b) More accurate method: replace the hot end thermistor by a 100K 1% resistor and adjust the H parameter to get a reading as close to 25C as possible (you probably won't manage exactly 25.0C because the DAC quantum is about 0.6C at this temperature). Then substitute a 220 ohm 1% resistor and adjust the L parameter to get a reading of 260.1C. Then change the resistor back to 100K, check you are still getting a reading close to 25C, and fine-tune the H parameter if necessary.

The parameters you use for the hot end should also be correct for the bed, so when you have determined the correct hot end parameters, send an M304 command with the same H and L parameters. However, you can use different M301 and M304 parameters if you wish.

EDIT: the values you end up with should be between about -100 and +100. For my own Duet I am using H18.2 L-14.

EDIT 2: changed above to use a 100K resistor instead of 220K.

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DC
Hi John, yes that's all correct. The ADC calibration has nothing to do with what hot end or z probe board you are using. The parameters have been moved from the M301 command to M305 by agreement with RepRapPro. The same H and L parameters you used with the M301 command (if you were using any) should be the correct ones to use with the M305 command, assuming you are using the same Duet board.