max31855.cpp

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#include "max31855.h"
 
#include "esphome/core/helpers.h"
#include "esphome/core/log.h"
 
namespace esphome::max31855 {
 
static const char *const TAG = "max31855";
 
void MAX31855Sensor::update() {
  this->enable();
  delay(1);
  // conversion initiated by rising edge
  this->disable();
 
  // Conversion time typ: 170ms, max: 220ms
  this->set_timeout("value", 220, [this]() { this->read_data_(); });
}
 
void MAX31855Sensor::setup() { this->spi_setup(); }
void MAX31855Sensor::dump_config() {
  ESP_LOGCONFIG(TAG, "MAX31855:");
  LOG_PIN("  CS Pin: ", this->cs_);
  LOG_UPDATE_INTERVAL(this);
  LOG_SENSOR("  ", "Thermocouple", this);
  if (this->temperature_reference_) {
    LOG_SENSOR("  ", "Reference", this->temperature_reference_);
  } else {
    ESP_LOGCONFIG(TAG, "  Reference temperature disabled.");
  }
}
void MAX31855Sensor::read_data_() {
  this->enable();
  delay(1);
  uint8_t data[4];
  this->read_array(data, 4);
  this->disable();
 
  const uint32_t mem = encode_uint32(data[0], data[1], data[2], data[3]);
 
  // Verify we got data
  if (mem != 0xFFFFFFFF) {
    this->status_clear_error();
  } else {
    ESP_LOGE(TAG, "No data received from MAX31855 (0x%08" PRIX32 "). Check wiring!", mem);
    this->publish_state(NAN);
    if (this->temperature_reference_) {
      this->temperature_reference_->publish_state(NAN);
    }
    this->status_set_error();
    return;
  }
 
  // Internal reference temperature always works
  if (this->temperature_reference_) {
    int16_t val = (mem & 0x0000FFF0) >> 4;
    if (val & 0x0800) {
      val |= 0xF000;  // Pad out 2's complement
    }
    const float t_ref = float(val) * 0.0625f;
    ESP_LOGD(TAG, "Got reference temperature: %.4f°C", t_ref);
    this->temperature_reference_->publish_state(t_ref);
  }
 
  // Check thermocouple faults
  if (mem & 0x00000001) {
    ESP_LOGW(TAG, "Thermocouple open circuit (not connected) fault from MAX31855 (0x%08" PRIX32 ")", mem);
    this->publish_state(NAN);
    this->status_set_warning();
    return;
  }
  if (mem & 0x00000002) {
    ESP_LOGW(TAG, "Thermocouple short circuit to ground fault from MAX31855 (0x%08" PRIX32 ")", mem);
    this->publish_state(NAN);
    this->status_set_warning();
    return;
  }
  if (mem & 0x00000004) {
    ESP_LOGW(TAG, "Thermocouple short circuit to VCC fault from MAX31855 (0x%08" PRIX32 ")", mem);
    this->publish_state(NAN);
    this->status_set_warning();
    return;
  }
  if (mem & 0x00010000) {
    ESP_LOGW(TAG, "Got faulty reading from MAX31855 (0x%08" PRIX32 ")", mem);
    this->publish_state(NAN);
    this->status_set_warning();
    return;
  }
 
  // Decode thermocouple temperature
  int16_t val = (mem & 0xFFFC0000) >> 18;
  if (val & 0x2000) {
    val |= 0xC000;  // Pad out 2's complement
  }
  const float t_sense = float(val) * 0.25f;
  ESP_LOGD(TAG, "Got thermocouple temperature: %.2f°C", t_sense);
  this->publish_state(t_sense);
  this->status_clear_warning();
}
 
}  // namespace esphome::max31855