I want to read data from PT1000 thermistor. After succeeding in communicating with the TouchGFX model and displaying the content I wanted, I now want to be able to read real time temp. For this job I have PT1000 sensor. I have made the ADC to work, but the problem I'm experiencing, is, that the values I get are very inaccurate. I'm getting every second different values in the range from 17 to 24 degrees, which is pretty bad. I aim for accuracy of +- 1 degree or even 0.1. Now it is quite miserable. I have placed 10uF capacitor to filter out noise, coded to get average of 10 convertions (excluding the lowest and highest values), but nothing helped, I mean, they have improoved the amplitudes, but not with the margin I expected. Before it was worse than 17-25. I really don't know what the reason could be. I have read a lot and watched and everyone has steady reading (for example 1723-1727 (12bit value straight from ADC)), I get fluctuations like 1723-2023. Maybe there is something wrong with my code, maybe there is problem with my channel, maybe it is EMI, but God this is one pretty big amplitude.
Please, help me with this problem, any suggestions are highly appreciated. This is my first contact with MCUs.
Here is my code. It is pretty dirty, in the end I was just hard trying stuff... :D
#define ADCx ADC1
#define ADCx_CLK_ENABLE() __HAL_RCC_ADC1_CLK_ENABLE()
#define ADCx_CHANNEL_GPIO_CLK_ENABLE() __HAL_RCC_GPIOA_CLK_ENABLE()
#define ADCx_FORCE_RESET() __HAL_RCC_ADC_FORCE_RESET()
#define ADCx_RELEASE_RESET() __HAL_RCC_ADC_RELEASE_RESET()
/* Definition for ADCx Channel Pin */
#define ADCx_CHANNEL_PIN GPIO_PIN_6
#define ADCx_CHANNEL_GPIO_PORT GPIOA
/* Definition for ADCx's Channel */
#define ADCx_CHANNEL ADC_CHANNEL_6
#define SAMPLINGTIME ADC_SAMPLETIME_480CYCLES
xQueueHandle msgQueueUI;
static void ADCTask(void* params)
{
ADC_HandleTypeDef AdcHandle;
/*
* Initialize ADC
*/
AdcHandle.Instance = ADCx;
if (HAL_ADC_DeInit(&AdcHandle) != HAL_OK)
{
/* ADC de-initialization Error */
while (1) {};
}
AdcHandle.Init.ClockPrescaler = ADC_CLOCKPRESCALER_PCLK_DIV4;
AdcHandle.Init.Resolution = ADC_RESOLUTION_12B;
AdcHandle.Init.DataAlign = ADC_DATAALIGN_RIGHT;
AdcHandle.Init.ScanConvMode = DISABLE;
AdcHandle.Init.EOCSelection = DISABLE;
AdcHandle.Init.ContinuousConvMode = DISABLE;
AdcHandle.Init.NbrOfConversion = 1;
AdcHandle.Init.DiscontinuousConvMode = DISABLE;
AdcHandle.Init.NbrOfDiscConversion = 0;
AdcHandle.Init.ExternalTrigConv = ADC_EXTERNALTRIGCONV_T1_CC1;
AdcHandle.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_NONE;
AdcHandle.Init.DMAContinuousRequests = DISABLE;
if (HAL_ADC_Init(&AdcHandle) != HAL_OK)
{
/* ADC initialization Error */
while (1) {};
}
GPIO_InitTypeDef GPIO_InitStruct;
/*##-1- Enable peripherals and GPIO Clocks #################################*/
/* ADC Periph clock enable */
ADCx_CLK_ENABLE();
/* Enable GPIO clock ****************************************/
ADCx_CHANNEL_GPIO_CLK_ENABLE();
/*##-2- Configure peripheral GPIO ##########################################*/
/* ADC Channel GPIO pin configuration */
GPIO_InitStruct.Pin = ADCx_CHANNEL_PIN;
GPIO_InitStruct.Mode = GPIO_MODE_ANALOG;
GPIO_InitStruct.Pull = GPIO_NOPULL;
HAL_GPIO_Init(ADCx_CHANNEL_GPIO_PORT, &GPIO_InitStruct);
ADC_ChannelConfTypeDef sConfig;
sConfig.Channel = ADCx_CHANNEL; /* Sampled channel number */
sConfig.Rank = 1; /* Rank of sampled channel number ADCx_CHANNEL */
sConfig.SamplingTime = SAMPLINGTIME; /* Sampling time (number of clock cycles unit) */
sConfig.Offset = 0; /* Parameter discarded because offset correction is disabled */
if (HAL_ADC_ConfigChannel(&AdcHandle, &sConfig) != HAL_OK)
{
/* Channel Configuration Error */
while (1) {};
}
float A=3.9083E-3; /* PT1000 consts */
float B=-5.775E-7; /* PT1000 consts */
float R = 1000; /* PT1000 consts */
float averageRead[10]; /* hard trying to improve accuracy */
while (1)
{
vTaskDelay(1000); //Approx 10 Hz
// Start Conversation Error
HAL_ADC_Start(&AdcHandle);
for(int i =0; i<10; i++){
HAL_ADC_PollForConversion(&AdcHandle, 10);
averageRead[i] = HAL_ADC_GetValue(&AdcHandle);
}
float maxValue = averageRead[0];
for(int i=1;i < 10;i++){
if(averageRead[i] > maxValue){
maxValue = averageRead[i];
}
}
float minValue = averageRead[0];
for(int i=1;i < 10;i++){
if(averageRead[i] > minValue){
minValue = averageRead[i];
}
}
float sum = 0;
for (int i=0;i<10;i++){
sum += averageRead[i];
}
float adcValue = (sum - minValue - maxValue)/8;
// Get the converted value of regular channel
float adcVoltage = adcValue*(3.3/4096);
float adcResistance = ((3.3*2200)-(adcVoltage * 2200)) / adcVoltage;
float adcTemp = ((R * A * (-1)) + sqrt((R * R * A * A) - (4 * R * B * (R - adcResistance))))/(2 * R * B); /* PT1000 formula */
xQueueSendToBack(msgQueueUI, &adcTemp, 0); /* sending value to model in TouchGFX */
}
}
P.s my question was posted empty at first, so I had to rewrite it, sorry
P.s. Degrees are in Celsius 🙂
P.s. Sorry for bad English
