Hello,
I am using the SparkFun IR Thermometer Evaluation Board - MLX90614 paired with and ESP32 feather V2 to read the temperature of an object and display certain LED colours. My system seems to work fine for a bit but then will randomly get “nan” readings from the sensor and need to restart to get fixed. Does anyone have any input into what might cause this? I have tested an entire new circuit already so it is unlikely to be hardware related.
Thank you,
Tim
#include <Wire.h>
#include <Adafruit_MLX90614.h>
// Create an MLX90614 object
Adafruit_MLX90614 mlx = Adafruit_MLX90614();
// Define LED pins (adjusted for ESP32 Feather)
const int LED1 = 32; // Lowest threshold
const int LED2 = 15; // Medium-low threshold
const int LED3 = 33; // Medium-high threshold
const int LED4 = 27; // Highest threshold
// Define Switch Pin
const int SWITCH_PIN = 13; // GPIO connected to the switch
// Define Power Control Pin for the sensor
const int SENSOR_POWER_PIN = 14; // GPIO 14 to power the MLX90614 sensor
// Custom I²C pin definitions
#define SDA_PIN 22 // GPIO 22 for SDA
#define SCL_PIN 20 // GPIO 20 for SCL
// Error tracking variables
int nanCount = 0;
unsigned long lastGoodReading = 0;
unsigned long sensorStartTime = 0;
const unsigned long MIN_SENSOR_WARMUP = 1000; // Min 1 second warmup
const unsigned long POWER_CYCLE_TIMEOUT = 15000; // 15 seconds timeout
// Temperature thresholds
const float TEMP_THRESHOLD_1 = 25.0;
const float TEMP_THRESHOLD_2 = 29.0;
const float TEMP_THRESHOLD_3 = 33.0;
// Error handling constants
const int MAX_NAN_COUNT = 3;
// Function prototypes
bool initializeSensor();
float getValidTemperature();
void cycleSensorPower();
void updateLEDs(float temperature);
void turnOffAllLEDs();
void displayErrorPattern();
void showStartupSequence();
void setup() {
Serial.begin(115200);
Serial.println(“Squash Ball Temperature Monitor - Initializing…”);
// Set up LED pins
pinMode(LED1, OUTPUT);
pinMode(LED2, OUTPUT);
pinMode(LED3, OUTPUT);
pinMode(LED4, OUTPUT);
turnOffAllLEDs(); // Turn off all LEDs at startup
// Set up switch pin with pull-up
pinMode(SWITCH_PIN, INPUT);
// Set up power control
pinMode(SENSOR_POWER_PIN, OUTPUT);
digitalWrite(SENSOR_POWER_PIN, LOW); // Initially power off
// Initialize I²C with custom pins
Wire.begin(SDA_PIN, SCL_PIN);
Wire.setClock(100000); // Set to 100kHz for better stability
// Show startup sequence
showStartupSequence();
Serial.println(“System ready. Switch to ON position to start.”);
}
void showStartupSequence() {
// Run a LED sequence to indicate system is starting up
for (int i = 0; i < 2; i++) {
digitalWrite(LED1, HIGH);
delay(100);
digitalWrite(LED2, HIGH);
delay(100);
digitalWrite(LED3, HIGH);
delay(100);
digitalWrite(LED4, HIGH);
delay(100);
turnOffAllLEDs();
delay(200);
}
}
bool initializeSensor() {
byte retries = 0;
const byte MAX_RETRIES = 3;
Serial.println(“Initializing MLX90614 sensor…”);
while (retries < MAX_RETRIES) {
if (mlx.begin()) {
Serial.println(“MLX90614 initialized successfully.”);
return true;
}
Serial.print(“Initialization attempt “);
Serial.print(retries + 1);
Serial.println(” failed. Retrying…”);
retries++;
delay(500);
}
Serial.println(“ERROR: Failed to initialize MLX90614 after multiple attempts.”);
return false;
}
float getValidTemperature() {
// Check if minimum warmup time has passed since sensor was powered on
if (millis() - sensorStartTime < MIN_SENSOR_WARMUP) {
delay(MIN_SENSOR_WARMUP - (millis() - sensorStartTime));
}
const byte MAX_ATTEMPTS = 3;
for (byte attempt = 0; attempt < MAX_ATTEMPTS; attempt++) {
// Try to get object temperature
float objTemp = mlx.readObjectTempC();
// Check if reading is valid and in reasonable range for a squash ball (10-50°C)
if (!isnan(objTemp) && objTemp > 10.0 && objTemp < 50.0) {
return objTemp;
}
// If object temperature failed, try ambient temperature as a test
float ambTemp = mlx.readAmbientTempC();
if (!isnan(ambTemp)) {
Serial.print("Object temp read failed, but ambient temp valid: ");
Serial.println(ambTemp);
// If we can read ambient but not object, the sensor is working but may
// not be able to get a reliable object reading
}
// Brief delay between attempts
delay(100);
}
return NAN;
}
void cycleSensorPower() {
Serial.println(“Power cycling the sensor…”);
// Turn off all LEDs during power cycle
turnOffAllLEDs();
// Power off the sensor
digitalWrite(SENSOR_POWER_PIN, LOW);
delay(1000); // Wait for power to fully discharge
// Power on the sensor
digitalWrite(SENSOR_POWER_PIN, HIGH);
// Record the time sensor was powered on
sensorStartTime = millis();
// Wait for the sensor to stabilize - MLX90614 needs time after power up
delay(2000);
// Attempt to reinitialize the sensor
if (initializeSensor()) {
Serial.println(“Sensor restarted successfully.”);
} else {
Serial.println(“WARNING: Sensor failed to restart properly.”);
displayErrorPattern();
}
}
void updateLEDs(float temperature) {
// Turn all LEDs off first
turnOffAllLEDs();
// Set LEDs based on temperature thresholds
if (temperature < TEMP_THRESHOLD_1) {
digitalWrite(LED1, HIGH); // Lowest temperature range
} else if (temperature >= TEMP_THRESHOLD_1 && temperature < TEMP_THRESHOLD_2) {
digitalWrite(LED2, HIGH); // Medium-low temperature range
} else if (temperature >= TEMP_THRESHOLD_2 && temperature < TEMP_THRESHOLD_3) {
digitalWrite(LED3, HIGH); // Medium-high temperature range
} else if (temperature >= TEMP_THRESHOLD_3) {
digitalWrite(LED3, HIGH); // High temperature range
digitalWrite(LED4, HIGH); // Using two LEDs for highest range
}
}
void turnOffAllLEDs() {
digitalWrite(LED1, LOW);
digitalWrite(LED2, LOW);
digitalWrite(LED3, LOW);
digitalWrite(LED4, LOW);
}
void displayErrorPattern() {
// Flash LEDs in an alternating pattern to indicate error
turnOffAllLEDs();
for (int i = 0; i < 3; i++) {
digitalWrite(LED1, HIGH);
digitalWrite(LED3, HIGH);
delay(200);
digitalWrite(LED1, LOW);
digitalWrite(LED3, LOW);
digitalWrite(LED2, HIGH);
digitalWrite(LED4, HIGH);
delay(200);
digitalWrite(LED2, LOW);
digitalWrite(LED4, LOW);
}
}
void loop() {
// Check if the switch is ON (LOW because of pull-up resistor)
if (digitalRead(SWITCH_PIN) == HIGH) {
// If sensor is powered off, turn it on and initialize
if (digitalRead(SENSOR_POWER_PIN) == LOW) {
digitalWrite(SENSOR_POWER_PIN, HIGH);
sensorStartTime = millis();
delay(1000);
if (!initializeSensor()) {
displayErrorPattern();
cycleSensorPower();
}
lastGoodReading = millis();
}
// Read temperature
float temperature = getValidTemperature();
if (!isnan(temperature)) {
// Valid reading - reset NaN count and update last good reading time
nanCount = 0;
lastGoodReading = millis();
// Update LEDs based on temperature
updateLEDs(temperature);
// Print temperature
Serial.print("Temperature: ");
Serial.print(temperature, 1);
Serial.println(" °C");
} else {
// Invalid reading (NaN)
nanCount++;
Serial.print("NaN reading detected (");
Serial.print(nanCount);
Serial.print(" of ");
Serial.print(MAX_NAN_COUNT);
Serial.println(")");
// Try to read another value from the sensor to help diagnose
float ambTemp = mlx.readAmbientTempC();
if (!isnan(ambTemp)) {
Serial.print("Ambient temperature is valid: ");
Serial.println(ambTemp);
} else {
Serial.println("Both object and ambient readings are invalid");
}
// If we exceed the max NaN count, power cycle
if (nanCount >= MAX_NAN_COUNT) {
Serial.println("Multiple NaN readings detected!");
cycleSensorPower();
nanCount = 0;
}
// Check for timeout since last good reading
if ((millis() - lastGoodReading) > POWER_CYCLE_TIMEOUT) {
Serial.println("Timeout since last good reading. Power cycling sensor.");
cycleSensorPower();
lastGoodReading = millis();
}
}
} else {
// Switch is OFF
turnOffAllLEDs();
// Power off the sensor if it's currently on
if (digitalRead(SENSOR_POWER_PIN) == HIGH) {
digitalWrite(SENSOR_POWER_PIN, LOW);
Serial.println("System powered OFF.");
}
// Reset counters
nanCount = 0;
delay(500); // Check switch state every half second
}
// Short delay for system stability
delay(200);
}