BMP085 / BMP180
This precision sensor from Bosch is the best low-cost sensing solution for measuring barometric pressure and temperature. Because pressure changes with altitude you can also use it as an altimeter! The sensor is soldered onto a PCB with a 3.3V regulator, I2C level shifter and pull-up resistors on the I2C pins.
We now have a fully 5V compliant version of this board - a 3.3V regulator and a i2c level shifter circuit is included so you can use this sensor safely with 5V logic and power
Using the sensor is easy. For example, if you`re using an Arduino, simply connect the VIN pin to the 5V voltage pin, GND to ground, SCL to I2C Clock (Analog 5) and SDA to I2C Data (Analog 4).