Arduino Sensor Data Serial Communication

Problem

Required Tools

Solution Steps

// === Circuit Wiring Diagram (ASCII) ===
//
//  Arduino Uno          DHT22 Sensor
//  +-----------+       +--------+
//  |           |       | 1(VCC) |----+---- 5V
//  |     5V  --+-------+--------+    |
//  |           |       | 2(DATA)|----+---- 10K resistor ---- 5V
//  |     D2  --+-------+--------+
//  |           |       | 3(NC)  |
//  |           |       +--------+
//  |    GND  --+-------| 4(GND) |-------- GND
//  +-----------+       +--------+
//
// Note: 3-pin module DHT22 has built-in pull-up resistor -> resistor can be omitted

# Install libraries via Arduino CLI
arduino-cli lib install "DHT sensor library"
arduino-cli lib install "Adafruit Unified Sensor"

# Verify installed libraries
arduino-cli lib list | grep -i dht

#include <DHT.h>

#define DHTPIN 2        // DHT22 data pin
#define DHTTYPE DHT22   // DHT22 (AM2302) sensor type

DHT dht(DHTPIN, DHTTYPE);

void setup() {
  Serial.begin(9600);   // Start serial communication (9600 baud)
  dht.begin();          // Initialize DHT sensor

  // Print CSV header
  Serial.println("temperature,humidity");

  // Wait for sensor stabilization
  delay(2000);
}

void loop() {
  // Read humidity (%)
  float humidity = dht.readHumidity();
  // Read temperature (Celsius)
  float temperature = dht.readTemperature();

  // Check for read failure
  if (isnan(humidity) || isnan(temperature)) {
    Serial.println("ERROR,ERROR");
    delay(2000);
    return;
  }

  // Serial output in CSV format
  Serial.print(temperature, 1);  // 1 decimal place
  Serial.print(",");
  Serial.println(humidity, 1);

  // DHT22 minimum sampling interval: 2 seconds
  delay(2000);
}

# Check serial monitor via Arduino CLI
arduino-cli monitor -p /dev/ttyACM0 -b arduino:avr:uno

# Or use minicom on Linux
minicom -b 9600 -D /dev/ttyACM0

# Use screen on macOS
screen /dev/cu.usbmodem14201 9600

#!/usr/bin/env python3
"""Arduino DHT22 sensor data collection script"""

import serial
import csv
import time
from datetime import datetime

# === Configuration ===
SERIAL_PORT = '/dev/ttyACM0'  # Windows: 'COM3', macOS: '/dev/cu.usbmodem14201'
BAUD_RATE = 9600
OUTPUT_FILE = f'sensor_data_{datetime.now():%Y%m%d_%H%M%S}.csv'
TEMP_THRESHOLD = 30.0   # Temperature alert threshold (degrees)
HUMID_THRESHOLD = 70.0  # Humidity alert threshold (%)

def main():
    # Connect to serial port
    ser = serial.Serial(SERIAL_PORT, BAUD_RATE, timeout=5)
    time.sleep(2)  # Wait for Arduino reset

    # Skip first line (header)
    header = ser.readline().decode('utf-8').strip()
    print(f"Sensor header: {header}")

    print(f"Data collection started... (output file: {OUTPUT_FILE})")
    print(f"Temp alert: > {TEMP_THRESHOLD} degrees, Humidity alert: > {HUMID_THRESHOLD}%")
    print("-" * 50)

    with open(OUTPUT_FILE, 'w', newline='') as csvfile:
        writer = csv.writer(csvfile)
        writer.writerow(['timestamp', 'temperature', 'humidity'])

        try:
            while True:
                line = ser.readline().decode('utf-8').strip()
                if not line or line.startswith('ERROR'):
                    print(f"[{datetime.now():%H:%M:%S}] Sensor read error")
                    continue

                parts = line.split(',')
                if len(parts) != 2:
                    continue

                temp, humid = float(parts[0]), float(parts[1])
                timestamp = datetime.now().isoformat()

                # Write to CSV file
                writer.writerow([timestamp, temp, humid])
                csvfile.flush()  # Write immediately

                # Console output
                alert = ""
                if temp > TEMP_THRESHOLD:
                    alert += " [HIGH TEMP WARNING!]"
                if humid > HUMID_THRESHOLD:
                    alert += " [HIGH HUMIDITY WARNING!]"

                print(f"[{datetime.now():%H:%M:%S}] "
                      f"Temp: {temp:.1f} deg | Humidity: {humid:.1f}%{alert}")

        except KeyboardInterrupt:
            print(f"\nCollection stopped. Data saved to: {OUTPUT_FILE}")
        finally:
            ser.close()

if __name__ == '__main__':
    main()

Core Code

Core code for the Arduino sketch and Python serial collector. Transmits DHT22 sensor data in CSV format and saves it to a file with timestamps.

// ===== Arduino Sketch (Core Code) =====
#include <DHT.h>

#define DHTPIN 2
#define DHTTYPE DHT22
DHT dht(DHTPIN, DHTTYPE);

void setup() {
  Serial.begin(9600);
  dht.begin();
  Serial.println("temperature,humidity");
  delay(2000);
}

void loop() {
  float h = dht.readHumidity();
  float t = dht.readTemperature();
  if (isnan(h) || isnan(t)) {
    Serial.println("ERROR,ERROR");
  } else {
    Serial.print(t, 1);
    Serial.print(",");
    Serial.println(h, 1);
  }
  delay(2000);
}

// ===== Python Collector (Core Code) =====
// pip install pyserial
//
// import serial, csv
// from datetime import datetime
//
// ser = serial.Serial('/dev/ttyACM0', 9600, timeout=5)
// ser.readline()  # Skip header
//
// with open('data.csv', 'w', newline='') as f:
//     w = csv.writer(f)
//     w.writerow(['time', 'temp', 'humid'])
//     while True:
//         line = ser.readline().decode().strip()
//         if line and 'ERROR' not in line:
//             t, h = line.split(',')
//             w.writerow([datetime.now().isoformat(), t, h])
//             f.flush()

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