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Cover image for LM35 vs BMP180: Comparing two budget temperature sensors
Payam Hoseini
Payam Hoseini

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LM35 vs BMP180: Comparing two budget temperature sensors

#iot #esp8266 #arduino #programming

A project comparing temperature accuracy between an LM35 analog sensor and a BMP180 barometric sensor, with pressure/altitude measurements.

Early Conclusion:

  • LM35 is more accurate for temperature.
  • BMP180 is not accurate as LM35 is, but provides pressure/altitude measurements. I've also tested DHT11 sensor previously and i can tell you that LM35 is so better and more accurate than DHT11, but if you want humidity beside temperature and price is not matter for your project, DHT22 is a better choice.

👉 You can find the full source code here:

GitHub Repo: payamhsn/Iot-LM35-vs-BMP180-Temp

🚀 Project Overview

This project compares:

  • LM35 (analog temperature sensor)
  • BMP180 (digital barometric sensor for temperature, pressure, and altitude)

Key Findings:

  • The LM35 is more accurate for temperature (~24.44°C vs room thermometer: 24°C).
  • The BMP180 reads slightly higher (~26.10°C) due to internal heat but provides useful pressure/altitude data.

🔍 How the Sensors Work

LM35 Temperature Sensor

  • Principle: Linear analog output (10mV/°C).
  • Accuracy: ±0.5°C at 25°C.
  • No calibration needed – directly outputs Celsius.
  • Formula: Temp (°C) = (ADC Reading × 500) / 1023
  • Pros: Simple, low-cost, reliable.
  • Cons: Only measures temperature.

BMP180 Barometric Sensor

  • Measures:
  • Temperature (°C)
  • Pressure (hPa)
  • Altitude (meters, derived from pressure)
  • Interface: I²C (SDA: A4, SCL: A5 on Arduino Uno).
  • How it calculates altitude: Altitude = 44330 × (1 − (P/P₀)^(1/5.255)) Where:
  • P = Measured pressure
  • P₀ = Sea-level pressure (1013.25 hPa default)
  • Pros: Multi-functional (pressure/altitude).
  • Cons: Temperature may drift due to internal heat.

🔧 Hardware Setup

BMP180 Pinout
BMP180 Pinout

LM35 Pinout
LM35 Pinout

Wiring Diagram

Sensor Arduino Uno Pin
LM35 A0 (Analog)
BMP180 I²C (SDA:A4, SCL:A5)

Circuit Setup:

  • LM35:
  • VCC → 5V
  • GND → GND
  • OUT → A0
  • BMP180:
  • VCC → 3.3V or 5V
  • GND → GND
  • SCL → A5
  • SDA → A4

Wiring Diagram connecting LM35 and BMP180 to Arduino Uno

My Wiring

My Wiring for connecting LM35 and BMP180 to Arduino Uno

💻 Code Explanation

The Arduino code:

  1. Reads LM35 (analog voltage → temperature).
  2. Reads BMP180 (temperature, pressure, altitude).
  3. Calculates the difference between the two sensors.
  4. Prints data to Serial Monitor every 10 seconds.

Key Libraries:

  • Wire.h (I²C communication)
  • Adafruit_BMP085.h (BMP180 sensor driver)

📊 Serial Monitor Output

Sensor Data:
LM35 Temperature: 24.44 °C
BMP180 Temperature: 26.10 °C
Temperature Difference (BMP-LM35): 1.66 °C
BMP180 Pressure: 879.85 hPa
BMP180 Altitude: 1174.28 meters

🔎 Observations & Analysis

  1. Temperature Difference (1.66°C):
    • BMP180 tends to read higher due to internal heat from pressure sensing.
    • LM35 is more reliable for ambient temperature.
  2. Pressure & Altitude:
    • Lower pressure (879.85 hPa) indicates higher altitude (1174m).
    • Useful for weather tracking or elevation-based projects.

After hours of running LM35, i found that its get more and more accurate comparing to my other pro sensor.

I wrote most of this blog by myself and a little help of AI. Thanks!

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