The BMA250E is a triaxial, low-g acceleration sensor with digital output for consumer applications.
It allows measurements of acceleration in three perpendicular axes. An evaluation circuitry (ASIC) converts the output of a micromechanical acceleration-sensing structure (MEMS) that works according to the differential capacitance principle.Package and interfaces of the BMA250E have been defined to match a multitude of hardware requirements.
Since the sensor features an ultra-small footprint and a flat package it is ingeniously suited for mobile applications.
The BMA250E offers a variable VDDIO voltage range from 1.2V to 3.6V and can be programmed to optimize functionality, performance and power consumption in customer specific applications.
A typical module
technical Information
| Parameter | Technical data |
|---|---|
| Digital resolution | 10 bit |
| Resolution (in ±2g range) |
3.9 mg |
| Measurement ranges (programmable) |
±2 g, ±4 g, ±8 g, ±16 g |
| Sensitivity (calibrated) | ±2 g: 256 LSB/g ±4 g: 128 LSB/g ±8 g: 64 LSB/g ±16 g: 32 LSB/g |
| Zero-g offset (typ., over life-time) | ±80 mg |
| Noise density (typ.) | 400 μg/√Hz |
| Bandwidths (programmable) | 1000 Hz … 8 Hz |
| Digital inputs/outputs | SPI & I²C, 2x digital interrupt pins |
| Supply voltage (VDD) | 1.62 V … 3.6 V |
| I/0 supply voltage (VDDIO) | 1.2 V … 3.6 V |
| Temperature range | -40 … +85°C |
| Current consumption – full operation – low-power mode |
130 μA (@ 2 kHz data rate) 6.5 μA (@ 40 Hz data rate) |
| LGA package | 2 x 2 x 0.95 mm³ |
| Interrupts | – Data-ready (e. g. for processor synchronization) – Any-motion (slope) detection (e. g. for wake-up) – Tap sensing (e. g. for tap-sensitive UI control) – Orientation change recognition (e. g. for portrait/landscape switching) – Flat detection (e. g. for position sensitive switching) – Low-g / high-g detection (e. g. for shock and free-fall detection) – No-motion (e.g. for power saving) |
Parts Required
Connection
| Beaglebone | Module |
| 3.3v – P9.3 | Vcc |
| Gnd – P9.1 | Gnd |
| SDA – P9.20 | SDA |
| SCL – P9.19 | SCL |
Code
[codesyntax lang=”python”]
import smbus import time # Get I2C bus bus = smbus.SMBus(2) # BMA250 address, 0x18(24) # Select range selection register, 0x0F(15) # 0x03(03) Set range = +/-2g bus.write_byte_data(0x19, 0x0F, 0x03) # BMA250 address, 0x18(24) # Select bandwidth register, 0x10(16) # 0x08(08) Bandwidth = 7.81 Hz bus.write_byte_data(0x19, 0x10, 0x08) time.sleep(0.5) # BMA250 address, 0x18(24) # Read data back from 0x02(02), 6 bytes # X-Axis LSB, X-Axis MSB, Y-Axis LSB, Y-Axis MSB, Z-Axis LSB, Z-Axis MSB data = bus.read_i2c_block_data(0x19, 0x02, 6) # Convert the data to 10 bits xAccl = (data[1] * 256 + (data[0] & 0xC0)) / 64 if xAccl > 511 : xAccl -= 1024 yAccl = (data[3] * 256 + (data[2] & 0xC0)) / 64 if yAccl > 511 : yAccl -= 1024 zAccl = (data[5] * 256 + (data[4] & 0xC0)) / 64 if zAccl > 511 : zAccl -= 1024 # Output data to screen print "Acceleration in X-Axis : %d" % xAccl print "Acceleration in Y-Axis : %d" % yAccl print "Acceleration in Z-Axis : %d" % zAccl
[/codesyntax]
Output
You can see a few runs, moving the sensor below
debian@beaglebone:/var/lib/cloud9/$ python bma250.py
Acceleration in X-Axis : 143
Acceleration in Y-Axis : 192
Acceleration in Z-Axis : 99
debian@beaglebone:/var/lib/cloud9/$ python bma250.py
Acceleration in X-Axis : 143
Acceleration in Y-Axis : 188
Acceleration in Z-Axis : 105
debian@beaglebone:/var/lib/cloud9/$ python bma250.py
Acceleration in X-Axis : 158
Acceleration in Y-Axis : 176
Acceleration in Z-Axis : 39
debian@beaglebone:/var/lib/cloud9/$ python bma250.py
Acceleration in X-Axis : 152
Acceleration in Y-Axis : 199
Acceleration in Z-Axis : -41
