Cant read bed temperature

Hello all,

im in the progress to update my repetier software (host + firmware) and i cant read the bed temperature.
I used the online-firmware-configurator, worked like a charm.

My Hardware:
-Megatronics V3.1 Board
-Smartcontroller (RepRapDiscount)
-Raspberry Pi 2b with Repetier-Server 1.0.4 Pro (will update this the next days)
-uploading firmware with the repetier-server fw-upload function

My Problem is i cant get any temperature for the heated bed, no matter what pin i assign.

// Extruder 1 - Thermistor 1
#define TEMP_0_PIN 15
// Extruder 2 - Thermistor 2
#define TEMP_2_PIN 14
// Extruder 3 - Thermistor 3
#define TEMP_3_PIN 13
// Heated bed - Thermistor 4
#define TEMP_1_PIN 12

the pins are correct according to the megatronics-datasheet.

Heres the strange part:
i can only read the temperatures for extruder 1+2, heated bed is always 0°C.
I can change the pin in the code so extruder 1 reads the heated bed sensor, this works with all thermistor inputs correctly.

It seems like the code for the heated bed variable does no read anything. Usually a open pin shows -20°C.

Is this a known problem?



  • Normally our numbering is TEMP_1_PIN for bed, but all what matters is where you connected it. If you read docs megatronicsv3.pdf
    page 13 you see thermistors are analog pins 12-15 so if you have connected it to one of them, that should give the correct reading. Since it is working with one of the extruder pins the reading function it self is correct.
    On same page you also see pins are also digital pins D66-D69 - so to work correctly none of the functions is allowed to these pin number or they would interfere and last one setting function wins.

    Do you have set a correct thermistor type for the bed? Only input pin and sensor type have influence on the value you see. Or do you have not activated bed at all? What does M105 return in console? Do you see the bed there?
  • I have a BQ Hephestos and I have the same problem with Repetier firmware.
    With Marlin 1.3.1 I read the bed temp.
    Any help, please?
  • If you have no output for bed with M105 you have not enabled bed support.
  • The bed is enabled, but temperature gives always -15º
  • Ok, then bed is configured wrong. -15 is the minimum tempertature for the selected thermistor I think, so you are not reading the analog value from the sensor, but from an unconnected pin. Note that TEMP_1_PIN is normally the pin for bed. Try to put sensor into the other slots and see for which it reports a normal temperature, then you know which pins it is reading with current settings.
  • I change the thermistor and change pin (14 to 15)
    Now the min temp is +/- 112º
    How can I solve it?
  • Have you measured the thermistor resistance? At room temperature it should be around 100kOhm. Just to be sure it is a thermistor and not a thermo-couple. Thermocouple have nearly no resistance and require a different circuit for measuring.
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