DIY Over-Temperature Alarm System using ESP32-S3 and LM35 in MicroPython

In this tutorial, we will build a smart Over-Temperature Alarm System using an ESP32-CAM microcontroller, an LM35 precision temperature sensor, and an audible speaker/buzzer. We will write the firmware in MicroPython and simulate the entire circuit in Proteus EDA.

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🛠️ Components Required

• ESP32-CAM Microcontroller Board
• LM35 Precision Analog Temperature Sensor
• Speaker or Piezo Buzzer
• 5V Power Supply & Ground

📐 Circuit Connections & Pin Mapping

Circuit Diagram 

Component	Pin	Connected To (ESP32-CAM)	Description
LM35 Sensor	Pin 1 (+VS)	+5V	Power Supply
LM35 Sensor	Pin 2 (VOUT)	GPIO 12 (GP12)	Analog Temperature Signal
LM35 Sensor	Pin 3 (-VS)	GND	Ground
Speaker/Buzzer	Pin 1	GPIO 16 (GP16)	PWM Audio Output
Speaker/Buzzer	Pin 2	GND	Ground

🐍 MicroPython Source Code (main.py)

from machine import Pin, ADC, PWM
import time

# 1. Configure ADC on GPIO 12 for the LM35 sensor
adc = ADC(Pin(12))

# 2. Configure PWM on GPIO 16 for the Speaker/Buzzer
buzzer = PWM(Pin(16))
buzzer.duty_u16(0)  # Start with buzzer turned OFF

# 3. Alarm Threshold in Celsius
ALARM_THRESHOLD = 50.0

print("=========================================")
print("  LM35 Temperature Alarm System Started  ")
print("  Threshold set to: 50.0 °C             ")
print("=========================================")

while True:
    # Read raw 16-bit ADC value (0 to 65535)
    raw_value = adc.read_u16()
    
    # Convert using calibrated 0.924V reference voltage
    voltage = (raw_value / 65535.0) * 0.924
    
    # Convert voltage to Celsius (LM35 = 10mV per degree C)
    temp_c = voltage * 100.0
    
    # Check if temperature exceeds 50 °C
    if temp_c > ALARM_THRESHOLD:
        # Sound the Alarm (1000 Hz tone at 50% duty cycle)
        buzzer.freq(1000)
        buzzer.duty_u16(32768)
        
        status = "ALARM! Temp exceeds 50C!"
    else:
        # Turn OFF the Alarm
        buzzer.duty_u16(0)
        status = "NORMAL"
    
    # Print real-time reading to the console
    print("Temp: {:5.1f} C | Status: {}".format(temp_c, status))
    
    time.sleep(0.5)

🔬 How the Circuit Works

1. Sensing: The LM35 outputs an analog voltage proportional to temperature (10mV per °C). For example, at 27°C, the output is 0.27V.
2. Digitization: The ESP32-CAM internal ADC reads this voltage on GPIO 12 and converts it into a 16-bit digital integer (0 to 65535).
3. Processing: The MicroPython code calculates the exact temperature:
   Voltage = (ADC Reading / 65535) * 0.924 V
Temp (°C) = Voltage * 100
4. Alarm Trigger: If the calculated temperature exceeds 50.0°C, the ESP32-CAM activates a 1000 Hz PWM square wave on GPIO 16, driving the speaker to sound a loud alert tone.