Has anyone ever experience an opposite temperature change readout from a thermistor connected to Ramps 1.4 running current Marlin?
Marlin 1.1.8
Arduino Mega 2560 R3
Ramps 1.4
12864 LCD w/SD Card Support
100K Thermistor - generic thermistor included with the Ramps/Driver/Heated Plate/LCD combo package I purchased from ebay.
I verified the thermistor is working properly by checking the resistance with my DMM - at 25ºC the resistance is around 101kohm. I also checked and verified that the resistance measured decreases as the temperature of the thermistor increases.
The readout on the LCD with the thermistor connected to the ramps T0 slot shows 25ºC at the room temp of 25ºC, but when I place the sensor between my fingers(increasing the temperature), the temp readout on the LCD decreases gradually down to around 20ºC). Both the LCD readout and sensor are changing values in response to a temperature change, but the direction of temperature change is backwards.
I’m pretty sure there is no polarity on a thermistor, but have tried reversing the connection on the board anyway with no change. I have also tried various options for #define TEMP_SENSOR_0 (1,11,13) with a re-upload to the board after each change, as well as tried the different physical slots on the ramps board(T0,T1,T2) and ended up with the same results.
I’m guessing the solution is something simple like commenting out a line in the firmware or selecting a specific sensor/table. I’ve searched the web for a solution from others having this problem, but I couldn't find any mention of a similar experience.
Does this sound like something obvious to anyone more familiar with 100k thermistors or Marlin?
I can perform further tests and report the results if you need more information.
Any help is greatly appreciated!
~Walter~
Marlin 1.1.8
Arduino Mega 2560 R3
Ramps 1.4
12864 LCD w/SD Card Support
100K Thermistor - generic thermistor included with the Ramps/Driver/Heated Plate/LCD combo package I purchased from ebay.
I verified the thermistor is working properly by checking the resistance with my DMM - at 25ºC the resistance is around 101kohm. I also checked and verified that the resistance measured decreases as the temperature of the thermistor increases.
The readout on the LCD with the thermistor connected to the ramps T0 slot shows 25ºC at the room temp of 25ºC, but when I place the sensor between my fingers(increasing the temperature), the temp readout on the LCD decreases gradually down to around 20ºC). Both the LCD readout and sensor are changing values in response to a temperature change, but the direction of temperature change is backwards.
I’m pretty sure there is no polarity on a thermistor, but have tried reversing the connection on the board anyway with no change. I have also tried various options for #define TEMP_SENSOR_0 (1,11,13) with a re-upload to the board after each change, as well as tried the different physical slots on the ramps board(T0,T1,T2) and ended up with the same results.
I’m guessing the solution is something simple like commenting out a line in the firmware or selecting a specific sensor/table. I’ve searched the web for a solution from others having this problem, but I couldn't find any mention of a similar experience.
Does this sound like something obvious to anyone more familiar with 100k thermistors or Marlin?
I can perform further tests and report the results if you need more information.
Any help is greatly appreciated!
~Walter~