LM35 vs BMP180: Comparing two budget temperature sensors

[Lomanu4]

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:

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? 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

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LM35 Pinout

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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

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My Wiring

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? 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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