Saturday, November 30, 2013

Enabling Dual Thermistor Support in Marlin

The J-Head Mk VI-B has two thermistor holes and can have redundant thermistors in in order to ensure that the failure of one thermistor does not result in the failure of the PEEK nozzle holder.

In order to enabling dual thermistor support, for one hot-end, the latest version of Marlin needs to be installed. In Marlin, the thermistors are referenced as "TEMP_SENSOR_x", where x is the number of the thermistor.

Starting on line 123, of Configuration.h, is the following code:

#define TEMP_SENSOR_0 -1
#define TEMP_SENSOR_1 -1
#define TEMP_SENSOR_2 0
#define TEMP_SENSOR_BED 0
// This makes temp sensor 1 a redundant sensor for sensor 0. If the temperatures difference between these sensors is to high the print will be aborted.
//#define TEMP_SENSOR_1_AS_REDUNDANT
#define MAX_REDUNDANT_TEMP_SENSOR_DIFF 10

This code will have to be changed so that it is similar to the following:

#define TEMP_SENSOR_0 5
#define TEMP_SENSOR_1 5
#define TEMP_SENSOR_2 0
#define TEMP_SENSOR_BED 0
// This makes temp sensor 1 a redundant sensor for sensor 0. If the temperatures difference between these sensors is to high the print will be aborted.
#define TEMP_SENSOR_1_AS_REDUNDANT
#define MAX_REDUNDANT_TEMP_SENSOR_DIFF 10

The above changes define two type 5 thermistors for the hot-end. (The thermistor type table is just before this code snippet.) In addition, thermistor number 1 is set to be redundant to thermistor number 0. (#define TEMP_SENSOR_1_AS_REDUNDANT turns on this feature.) The last line sets the maximum allowed temperature difference between the two thermistors before the firmware aborts the print.

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