LPC55S16-EVK - Temperature sensor reads

[embedded_eng_]

Hi all,

I'm using LPC55S16-EVK, and I'm trying to add temperature reads using the built in temperature sensor to my application.

I followed lpcxpresso55s16_lpadc_temperature_measurement example.

Here is my code:

ADC initialization

void init_adc_peripheral()
{
  const lpadc_config_t config = {
    .enableInDozeMode = true,
    .conversionAverageMode = kLPADC_ConversionAverage128,
    .enableAnalogPreliminary = true,
    .powerUpDelay = 0x80UL,
    .referenceVoltageSource = ADC_REF,
    .powerLevelMode = kLPADC_PowerLevelAlt1,
    .triggerPriorityPolicy = kLPADC_TriggerPriorityPreemptImmediately,
    .enableConvPause = false,
    .convPauseDelay = 0UL,
    .FIFO0Watermark = 0UL,
    .FIFO1Watermark = 0UL
  };

  POWER_DisablePD(kPDRUNCFG_PD_LDOGPADC);

  LPADC_Init(ADC_BASE, &config);

  LPADC_DoOffsetCalibration(ADC_BASE);

  LPADC_DoAutoCalibration(ADC_BASE);
}

Command initialization

void init_adc_command()
{
  const lpadc_conv_command_config_t config = {
    .sampleChannelMode = kLPADC_SampleChannelSingleEndSideA,
    .channelNumber = 26,
    .chainedNextCommandNumber = 0,
    .enableAutoChannelIncrement = false,
    .loopCount = 0UL,
    .hardwareAverageMode = kLPADC_HardwareAverageCount1,
    .sampleTimeMode = kLPADC_SampleTimeADCK3,
    .hardwareCompareMode = kLPADC_HardwareCompareDisabled,
    .hardwareCompareValueHigh = 0UL,
    .hardwareCompareValueLow = 0UL,
    .conversionResolutionMode = kLPADC_ConversionResolutionHigh,
    .enableWaitTrigger = false
  };

  LPADC_SetConvCommandConfig(ADC_BASE, 3, &config);
}

Trigger initialization

void init_adc_trigger()
{
  const lpadc_conv_trigger_config_t config = {
    .targetCommandId = 3,
    .delayPower = 0,
    .priority = 0,
    .channelAFIFOSelect = 0,
    .channelBFIFOSelect = 0,
    .enableHardwareTrigger = false
  };

  LPADC_SetConvTriggerConfig(ADC_BASE, 2, &config);
}

Function to read temperature sensor:

uint32_t read_adc()
{
  lpadc_conv_result_t config;

  /*trigger ADC read*/
  LPADC_DoSoftwareTrigger(ADC_BASE, 4);

  /*wait for result*/
  while (!LPADC_GetConvResult(ADC_BASE, &config, 0U)){};
  /*return data*/
  return (uint32_t) config.convValue;
}


float calculate_temperature()
{
  uint16_t Vbe1            = 0U;
  uint16_t Vbe8            = 0U;
  uint32_t convResultShift = 3U;
  float parameterSlope     = DEMO_LPADC_TEMP_PARAMETER_A;
  float parameterOffset    = DEMO_LPADC_TEMP_PARAMETER_B;
  float parameterAlpha     = DEMO_LPADC_TEMP_PARAMETER_ALPHA;
  float temperature        = -273.15f; /* Absolute zero degree as the incorrect return value. */

  /* If the temperature sensor need calibration, then read the calibration from the flash. */
  uint32_t temperatureSlopeSolidifyValue  = (*((volatile uint32_t *)(FSL_FEATURE_FLASH_NMPA_TEMP_SLOPE_ADDRS)));
  uint32_t temperatureOffsetSolidifyValue = (*((volatile uint32_t *)(FSL_FEATURE_FLASH_NMPA_TEMP_OFFSET_ADDRS)));

  if (((temperatureSlopeSolidifyValue & 0x1UL) != 0UL) && ((temperatureOffsetSolidifyValue & 0x1UL) != 0UL))
  {
      /* Rejustify slope value and Offset value based on the calibration value. */
      parameterSlope  = ((float)(uint32_t)(temperatureSlopeSolidifyValue >> 1UL) / 1024.0f);
      parameterOffset = ((float)(uint32_t)(temperatureOffsetSolidifyValue >> 1UL) / 1024.0f);
  }


      Vbe1 = read_adc() >> convResultShift;

      Vbe8 = read_adc() >> convResultShift;
          /* Final temperature = A*[alpha*(Vbe8-Vbe1)/(Vbe8 + alpha*(Vbe8-Vbe1))] - B. */
          temperature = parameterSlope * (parameterAlpha * ((float)Vbe8 - (float)Vbe1) /
                                          ((float)Vbe8 + parameterAlpha * ((float)Vbe8 - (float)Vbe1))) -
                        parameterOffset;

  return temperature;
}

The output I get is around the value: 582.

What I'm doing wrong? 

Thanks!

[embedded_eng_ · Accepted solution]

Hi @PabloAvalos, thanks for your reply.

I found the problem, I had to use different parameters for the ADC command

  const lpadc_conv_command_config_t config = {
    .sampleChannelMode = kLPADC_SampleChannelDiffBothSide,
    .channelNumber = 26,
    .chainedNextCommandNumber = 0,
    .enableAutoChannelIncrement = false,
    .loopCount = FSL_FEATURE_LPADC_TEMP_SENS_BUFFER_SIZE - 1U,
    .hardwareAverageMode = kLPADC_HardwareAverageCount128,
    .sampleTimeMode = kLPADC_SampleTimeADCK131,
    .hardwareCompareMode = kLPADC_HardwareCompareDisabled,
    .hardwareCompareValueHigh = 0UL,
    .hardwareCompareValueLow = 0UL,
    .conversionResolutionMode = kLPADC_ConversionResolutionHigh,
    .enableWaitTrigger = false
  };

And I had to reset the FIFOs after an ADC read.

[PabloAvalos]

Hi @embedded_eng_ 

Thank you so much for reaching us in our community.

Hope you are well, I would like to ask, what did you change on the SDK example? and which SDK version you are using for the lpadc_temperature_measurement ? Because the conversion for temperature has to be ok.

I will be here to help you, I really appreciate your reply. Please let me know if you have more concerns.

Best Regards.
Pablo Avalos.