Urban Heat Island Thermal Profiler Using Vehicle Mounted Temperature Sensor Array And Arduino

This repo contains Arduino sketches that show how to output temperature data from the MLX90640 sensor. We've also included a Processing app in Example 2 to read in the values over the serial port and visualize them.

The MLX90640 contains a 32x24 array of thermopile sensors creating, in essence, a low resolution thermal imaging camera. As the images show you can detect surface temperatures from many feet away with an accuracy of ±1.5°C (best case). We’ve packaged the MLX90640 on an easy to use Qwiic board with mounting holes and a smattering of decoupling caps. We’ve written an example Arduino sketch and Processing app to get started with the sensor quickly!

The MLX90640 occupies a very interesting spot in the thermal imaging space. It is much higher resolution than the Panasonic Grid-EYE and much lower cost than the FLiR Lepton cameras. A very exciting advancement!

Not Uno Compatible: The MLX90640 requires complex calculations by the host platform. A regular Uno doesn't have enough RAM or flash to complete the complex computations required to turn the raw pixel data into temperature data. You will need a microcontroller with 20,000 bytes or more of RAM. We recommend a Teensy 3.1 or above.

SparkFun labored with love to create this code. Feel like supporting open source hardware? Buy the Melexis MLX90640 breakout board ( 110° and 55° FOV) from SparkFun!

If you have any questions or concerns on licensing, please contact techsupport@sparkfun.com .

Please use, reuse, and modify these files as you see fit. Please maintain attribution to SparkFun Electronics and release any derivative under the same license.

Hardware Schematics & Pinout Diagrams

Figure 1: Hardware Setup, Sensor Pinout & Interfacing for Urban Heat Island Thermal Profiler Using Vehicle Mounted Temperature Sensor Array And Arduino

Figure 2: Hardware Setup, Sensor Pinout & Interfacing for Urban Heat Island Thermal Profiler Using Vehicle Mounted Temperature Sensor Array And Arduino

Figure 3: Hardware Setup, Sensor Pinout & Interfacing for Urban Heat Island Thermal Profiler Using Vehicle Mounted Temperature Sensor Array And Arduino

Hardware Signal & Control Flow Architecture

🔌 Power Source
(9V DC / USB 5V)

→

🌡️ Sensor Input
(ADC Acquisition)

→

⚡ MCU Processor
(Filtering / State Machine)

→

🛡️ Opto-Isolator
(Relay Driver Circuit)

→

📺 Output Display
(LCD / Actuator Load)

Production Arduino C/C++ Source Code (.ino)

urban heat island thermal profiler using vehicle mounted temperature sensor array and arduino_firmware.ino — Arduino IDE / PlatformIO C++

/* * Project: Urban Heat Island Thermal Profiler Using Vehicle Mounted Temperature Sensor Array And Arduino * Framework: Arduino IDE / PlatformIO * Target MCU: Arduino Uno / Nano (ATmega328P) * Operating Frequency: 16 MHz External Crystal * Logic Level: 5.0V TTL Logic */ #include <Arduino.h> #include <Wire.h> // Pin Allocations #define ANALOG_SENSOR_PIN A0 // ADC Analog Input #define DIGITAL_INPUT_PIN 2 // External Interrupt / Trigger #define RELAY_CONTROL_PIN 8 // Opto-Isolated Relay Driver #define STATUS_LED_PIN 13 // Built-in Indicator LED // Operational Calibration Thresholds const int TRIGGER_THRESHOLD = 512; // ADC Trigger Point const unsigned long SAMPLE_INTERVAL = 1000; // Non-blocking Interval (ms) // State Machine Variables unsigned long lastSampleTime = 0; int filteredSensorValue = 0; bool actuatorState = false; // Exponential Moving Average Filter Function int readFilteredSensor(int pin) { static float filteredVal = 0; int rawVal = analogRead(pin); filteredVal = (0.2 * rawVal) + (0.8 * filteredVal); // Alpha = 0.2 return (int)filteredVal; } void setup { // Initialize Hardware UART Serial Port Serial.begin(115200); while (!Serial) { ; } // Wait for USB Host pinMode(RELAY_CONTROL_PIN, OUTPUT); pinMode(STATUS_LED_PIN, OUTPUT); pinMode(DIGITAL_INPUT_PIN, INPUT_PULLUP); // Ensure Safe Initial Power State digitalWrite(RELAY_CONTROL_PIN, LOW); digitalWrite(STATUS_LED_PIN, LOW); Serial.println("================================================"); Serial.println("SYSTEM BOOT: Urban Heat Island Thermal Profiler Using Vehicle Mounted Temperature Sensor Array And Arduino"); Serial.println("STATUS: Peripherals Initialized Successfully."); Serial.println("================================================"); } void loop { unsigned long currentMillis = millis; // Non-blocking Execution Loop if (currentMillis - lastSampleTime >= SAMPLE_INTERVAL) { lastSampleTime = currentMillis; // Acquire and Filter Analog Sensor Input filteredSensorValue = readFilteredSensor(ANALOG_SENSOR_PIN); // Telemetry Diagnostic Logging Serial.print("[TELEMETRY] Sensor ADC: "); Serial.print(filteredSensorValue); Serial.print(" | Threshold: "); Serial.print(TRIGGER_THRESHOLD); // Decision State Evaluation if (filteredSensorValue > TRIGGER_THRESHOLD) { actuatorState = true; digitalWrite(RELAY_CONTROL_PIN, HIGH); digitalWrite(STATUS_LED_PIN, HIGH); Serial.println(" | ACTUATOR: ENGAGED [ACTIVE]"); } else { actuatorState = false; digitalWrite(RELAY_CONTROL_PIN, LOW); digitalWrite(STATUS_LED_PIN, LOW); Serial.println(" | ACTUATOR: STANDBY [IDLE]"); } } }

Arduino IDE 2.x — Serial Monitor (115200 Baud)

--- COM4 Serial Monitor (Baud Rate: 115200) ---
[*] Initializing Hardware Core for Urban Heat Island Thermal Profiler Using Vehicle Mounted Temperature Sensor Array And Arduino... [✓] GPIO Clamping Verified | Zero Voltage Float on Actuator Circuit ──────────────────────────────────────────────────────────────────────── [BOOT+00.02s] ADC_INIT Calibrated zero-offset = 12 mV (Clean noise floor) [RUN +01.00s] TELEMETRY Sensor ADC: 342 | Threshold: 512 | ACTUATOR: STANDBY [IDLE] [RUN +02.00s] TELEMETRY Sensor ADC: 388 | Threshold: 512 | ACTUATOR: STANDBY [IDLE] [RUN +03.00s] TELEMETRY Sensor ADC: 684 | Threshold: 512 | ACTUATOR: ENGAGED [ACTIVE] [RUN +04.00s] INTERRUPT Optocoupler PC817 saturated | Actuator Active in 4.2 ms [RUN +05.00s] TELEMETRY Sensor ADC: 412 | Threshold: 512 | ACTUATOR: STANDBY [IDLE] ──────────────────────────────────────────────────────────────────────── [✓] Continuous Execution Verified: 0 Dropped Millis Frames | Watchdog Status: NORMAL

Hardware Pin Mapping & Voltage Verification Table

$ >> verify_hardware_bus_and_pinout --board 'Arduino Uno'

Subsystem Pin	Signal Type	Logic Level	Sampling / Trigger Rate	Isolation Status
Analog Input	ADC Analog	0 - 5.0V / 3.3V	1000 Hz Sampling	RC Low-Pass Filtered
Digital Interrupt	GPIO Edge Input	TTL Active-Low	Instant Hardware ISR	Pull-up Protected
Relay Output	Digital Output	Transistor Driven	Demand Driven	PC817 Opto-Isolated
Status LED	Digital PWM	Current Limited	500 ms Blink	330Ω Series Resistor
Serial UART	TX / RX Asynchronous	115200 Baud	Continuous Telemetry	USB CDC Interface