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FRDM-KE06 Thermistor value never changes

Question asked by Sean Beatty on Apr 13, 2016
Latest reply on Apr 19, 2016 by Kerry Zhou

I have set-up the A2D on a FRDM-KE06Z board to monitor the Thermistor on channels 12 and 13, and also channel 15. The voltage I read on channels 12 and 13 never changes. Even though I put the board in the freezer for a couple hours, or touch a hot soldering iron to the Thermistor, I never see any change in the voltage. Any idea what's wrong?


Following is what I get for a channels 12, 13, 15, and some internal channels 22, 23, 29, and 30

     Thermistor High Volts: 2.474

     Thermistor Low Volts: 0.823

          Thermistor Temperature is: 25.0 degrees

     ADC Channel 15 Volts: 1.105

     Internal Temp sensor Volts: 1.461

          Internal Temperature is: 22.1 degrees

     Bandgap Volts: 1.067

     VREFH Volts: 3.301

     VREFL Volts: 0.000


I'm confident my A2D set-up is correct, since I get good readings on these other channels. That said, here's the A2D initialization code:

SIM_SCGC |= SIM_SCGC_ADC_MASK;    //Enable the clock to the ADC
//Clock must always be < 8MHz; must be < 4MHz in Low Pwr mode
ADC_SelectClockDivide(ADC_BASE_PTR, ADC_ADIV_DIVIDE_4); //20MHz / 4 = 5 MHz




//Setup the pins assoc with the following channels to ADC only - no GPIO functionality
ADC_APCTL1 = ((uint16_t)1<<ADC_CHANNEL_AD12)|((uint16_t)1<<ADC_CHANNEL_AD13)|((uint16_t)1<<ADC_CHANNEL_AD15);


ADC_SetLongSample(ADC_BASE_PTR); // Longer Sample time - higher accuracy!


    NVIC_EnableIRQ(INT_ADC);    //enable the ADC interrupt in NVIC.
   //Interrupt enable bit in ADC_SC1 is enabled later


Reading the ADC is simple:

    uint32_t u32temp;   

    u32temp = ADC_SC1;

    u32temp &= ~ADC_SC1_ADCH_MASK;

    ADC_SC1 = u32temp | 0xC; //This initiates the A2D conversion

  while( !ADC_IsCOCOFlag(pADC) ); //Wait for the conversion to complete

  return ADC_ReadResultReg(pADC);


Any idea why the Thermistor voltage doesn't change with temperature?


Thanks for your help!