Cheap Sensors : BMP085 - Pressure and Temperature
IntroductionFor 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 BoardsThe three boards I tested are:
- 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
The SetupAll 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|
The TestAll 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 ResultAll 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...