The BMP180 device is a digital barometric pressure sensor. This is available on a small module which provides access to the sensor via the I2C interface. This allows us to easily connect it to the Raspberry Pi with a minimum of wiring.
My module is a small pcb measuring 15x13mm with a 5 pin header. The order of the pins may vary on other modules so keep an eye on the labels so you connect up the correct wires from the Pi.
The BMP180 is made by Bosch and the official BMP180 datasheet includes all the technical details.
Configure I2C Interface
In order to use this module you must enable the I2C interface on the Raspberry Pi as it is not enabled by default. This is a fairly easy process and is described in my Enabling The I2C Interface On The Raspberry Pi tutorial.
Connecting Hardware
The table below shows how the module is connected to the Raspberyr Pi’s GPIO header (P1). Please refer to my GPIO header guide for a diagram.
| Module PCB | Desc | GPIO Header Pins |
|---|---|---|
| VCC | 3.3V | P1-01 |
| GND | Ground | P1-06 |
| SCL | I2C SCL | P1-05 |
| SDA | I2C SDA | P1-03 |
| 3.3V | – | – |
Here is a diagram of a breadboard setup. If you are connecting the module’s four pins directly to the Pi you only need four female-female wires.
The breadboard diagram uses a custom part I defined in Fritzing. Other modules are available which have different pin arrangements so make sure you are connecting the correct pins to the Pi if yours is different to the one shown in this tutorial.
With the device connected and the Pi powered up the “i2cdetect” command should show the device with address 0x77.
Example Python Script
Here is an example Python script to read pressure and temperature data from the sensor :
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#!/usr/bin/pythonimport smbusimport timefrom ctypes import c_short DEVICE = 0x77 # Default device I2C address #bus = smbus.SMBus(0) # Rev 1 Pi uses 0bus = smbus.SMBus(1) # Rev 2 Pi uses 1 def convertToString(data): # Simple function to convert binary data into # a string return str((data[1] + (256 * data[0])) / 1.2)def getShort(data, index): # return two bytes from data as a signed 16-bit value return c_short((data[index]<< 8) + data[index + 1]).valuedef getUshort(data, index): # return two bytes from data as an unsigned 16-bit value return (data[index]<< 8) + data[index+1]def readBmp180Id(addr=DEVICE): # Register Address REG_ID = 0xD0 (chip_id, chip_version) = bus.read_i2c_block_data(addr, REG_ID, 2) return (chip_id, chip_version) def readBmp180(addr=DEVICE): # Register Addresses REG_CALIB = 0xAA REG_MEAS = 0xF4 REG_MSB = 0xF6 REG_LSB = 0xF7 # Control Register Address CRV_TEMP = 0x2E CRV_PRES = 0x34 # Oversample setting OVERSAMPLE = 3 # 0 - 3 # Read calibration data # Read calibration data from EEPROM cal = bus.read_i2c_block_data(addr, REG_CALIB, 22) # Convert byte data to word values AC1 = getShort(cal, 0) AC2 = getShort(cal, 2) AC3 = getShort(cal, 4) AC4 = getUshort(cal, 6) AC5 = getUshort(cal, 8) AC6 = getUshort(cal, 10) B1 = getShort(cal, 12) B2 = getShort(cal, 14) MB = getShort(cal, 16) MC = getShort(cal, 18) MD = getShort(cal, 20) # Read temperature bus.write_byte_data(addr, REG_MEAS, CRV_TEMP) time.sleep(0.005) (msb, lsb) = bus.read_i2c_block_data(addr, REG_MSB, 2) UT = (msb << 8) + lsb # Read pressure bus.write_byte_data(addr, REG_MEAS, CRV_PRES + (OVERSAMPLE << 6)) time.sleep(0.04) (msb, lsb, xsb) = bus.read_i2c_block_data(addr, REG_MSB, 3) UP = ((msb << 16) + (lsb << 8) + xsb) >> (8 - OVERSAMPLE) # Refine temperature X1 = ((UT - AC6) * AC5) >> 15 X2 = (MC << 11) / (X1 + MD) B5 = X1 + X2 temperature = (B5 + 8) >> 4 # Refine pressure B6 = B5 - 4000 B62 = B6 * B6 >> 12 X1 = (B2 * B62) >> 11 X2 = AC2 * B6 >> 11 X3 = X1 + X2 B3 = (((AC1 * 4 + X3) << OVERSAMPLE) + 2) >> 2 X1 = AC3 * B6 >> 13 X2 = (B1 * B62) >> 16 X3 = ((X1 + X2) + 2) >> 2 B4 = (AC4 * (X3 + 32768)) >> 15 B7 = (UP - B3) * (50000 >> OVERSAMPLE) P = (B7 * 2) / B4 X1 = (P >> 8) * (P >> 8) X1 = (X1 * 3038) >> 16 X2 = (-7357 * P) >> 16 pressure = P + ((X1 + X2 + 3791) >> 4) return (temperature/10.0,pressure/ 100.0)def main(): (chip_id, chip_version) = readBmp180Id() print "Chip ID :", chip_id print "Version :", chip_version print (temperature,pressure)=readBmp180() print "Temperature : ", temperature, "C" print "Pressure : ", pressure, "mbar" if __name__=="__main__": main() |
It is recommended that you download this script directly to your Pi using the following command :
wget http://ift.tt/1KfFbXk
or use this link in a browser.
In order to run it you can use the following command :
sudo python bmp180.py
The output looks something like this :
The module is available from eBay, Amazon and many other online electronics shops.
View more at: http://yoursmart.mobi
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