Cheap Sensors : BMP085 - Pressure and Temperature

Introduction

For this post in my series on  'cheap sensors' I am looking at BMP085 sensors.  This is an extremely common pressure and temperature sensor available from many suppliers and on various break-out boards.

The Boards

The three boards I tested are:
  1. 10 Degree Of Freedom board
    • Unbranded (GY-80?) - £6.70 ebay China
      10 DOF (GY-80?)
      • L3G4200D - Digital gyro
      • ADXL345 - Digital accelerometer
      • HMV5883L - Digital compass
      • BMP085 - Barometric pressure
  2. Sparkfun BMP085 breakout - £13 from Proto-pic.co.uk
    Sparkfun BMP085
    • BMP085
  3. CJ-M32 - £2.65 from ebay China
    CJ-M32
    • BMP085

The Setup

All of the boards use 3.3 so some conversion is necessary when using a 5v Arduino.  The example on the Sparkfun website uses the 3.3v output to power the board, but then uses the 5v SDL and SCL lines directly from the Arduino ?

The two ebay boards both have 3.3v or 5v power inputs with an associated regulator; it should be noted that the data (SCL/SDL lines are not regulated so should (I assume) be leveled to 3.3v.  To ensure the best conditions I used a Sparkfun level convertor to drop the data lines to 3.3v.

BMP085 Test setup
If you have eagle eyes you might notice a DHL11 temperature sensor on the breadboard as I tested a few of these at the same time.

The Test

All of the sensors are I2C and worked with the same Arduino library so switching between them was easy.

I wired up each sensor and left it running for ~10 minutes and took averages of the temperature and pressure readings.  I compared the three sensor boards against a commercial weather station (cheap acctim) to see if they were at least comparable.

The Result

All three gave very similar pressure readings; which interestingly were about 6hPa below the commercial weather station.  I'm beginning to doubt my weather station.

The temperature readings of the two ebay sensors were within 0.2 degrees centigrade of the acctim station; the Sparkfun was slightly higher at ~0.7 degrees centigrade above the acctim station.

The Sparkfun website contains lots of help and libraries to support the developer and the board looks of a higher quality.

Ironically I used an Adafruit library to test the sensors (despite not having an Adafruit board - sorry Adafruit but difficult to get in the UK).  The Adafruit website and git repository has lots of great tutorials and libraries.

So in conclusion all performed within the published specs and would do the job required.  I tend to alternate between known suppliers (Sparkfun, Adafruit, etc) and cheap alternatives.

Hope this helps...

Comments

  1. The difference is constant between your pressure mesured and the commercial weather station???
    This difference may comes from the facts you don't live at the sea level. Do you live at 6*28=168 ft ? The weather station is probably calibrated.

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