LSM303D 3D Compass and Accelerometer Carrier with Voltage Regulator
The LSM303DLM combines a digital 3-axis accelerometer and 3-axis magnetometer into a single package that is ideal for making a tilt-compensated compass. The six independent readings, whose sensitivities can be set in the ranges of ±2 to ±8 g and ±1.3 to ±8.1 gauss, are available through an I²C interface. This LSM303 carrier board includes voltage regulators and a level-shifting circuit that allows operation from 2.6 to 5.5 V, and the 0.1" pin spacing makes it easy to use with standard solderless breadboards and 0.1" perfboards.
This board is a compact (0.5" × 0.9") breakout board for ST’s LSM303DLM 3-axis accelerometer and 3-axis magnetometer; we therefore recommend careful reading of the LSM303DLM datasheet (519k pdf) before using this product. The LSM303DLM is a great IC, but its small package makes it difficult for the typical student or hobbyist to use. The device also requires multiple voltage supplies not typically available when interfacing with 3.3 or 5 V systems. This carrier board addresses these issues by incorporating additional electronics, including two voltage regulators and a level-shifting circuit, while keeping the overall size as compact as possible. The board ships fully populated with its SMD components, including the LSM303.
The LSM303 has many configurable options, including dynamically selectable sensitivities for the accelerometer and magnetometer, a choice of output data rates, and two independently-programmable external inertial interrupt pins. The magnetometer and accelerometer can be individually turned on and off to save power, and a special sleep-to-wakeup function allows the accelerometer to sleep until an inertial interrupt is triggered. The six independent magnetic and acceleration readings (sometimes called 6DOF) are available through an I²C/TWI interface and can be used for many applications, including making a tilt-compensated compass that can be used to determine headings regardless of how the board is inclined (ST provides an application note (Find link below) that explains the details of making one).
The carrier board includes two voltage regulators that provide the 1.8 V and 3 V required by the LSM303, which allows the sensor to be powered from a single 2.6 – 5.5 V supply. The regulator outputs are available on the 1V8 and 3V pins and can supply almost 150 mA and 300 mA, respectively, to external devices. The breakout board also includes a circuit that shifts the I²C clock and data lines to the same logic voltage level as the supplied VIN, making it simple to interface the board with 3.3 V or 5 V systems, and the board’s 0.1" pin spacing makes it easy to use with standard solderless breadboards and 0.1" perfboards.
For sensor fusion applications, our MinIMU-9 inertial measurement unit combines the LSM303DLM with an L3G4200D 3-axis gyro on a board barely bigger than this LSM303DLM carrier alone, providing nine independent readings that can be used to calculate an absolute orientation.
- Dimensions: 0.5" × 0.9" × 0.1" (13 × 23 × 3 mm)
- Weight without header pins: 0.84 g (0.03 oz)
- Operating voltage: 2.6 to 5.5 V
- Supply current: 10 mA
- Output format (I2C):
- Accelerometer: one 12-bit reading (left-justified) per axis
- Magnetometer: one 12-bit reading (right-justified) per axis
- Sensitivity range (configurable):
- Accelerometer: ±2, ±4, or ±8 g
- Magnetometer: ±1.3, ±1.9, ±2.5, ±4.0, ±4.7, ±5.6, or ±8.1 gauss
The LSM303DLM readings can be queried and the device can be configured through the I²C bus. The module acts as two chained I²C slave devices, with the accelerometer and magnetometer clock and data lines tied together to the same I²C bus to ease communication. Additionally, level shifters on the I²C clock (SCL) and data lines (SDA) enable I²C communication with microcontrollers operating at the same voltage as VIN (2.6 – 5.5V). A detailed explanation of the protocol can be found in the LSM303DLM datasheet (Find link below).
The accelerometer and the magnetometer have separate 7-bit slave addresses on the I²C bus. The magnetometer’s slave address is 0011110b and cannot be changed. The accelerometer’s slave address has its least significant bit (LSb) determined by the voltage on the slave address selector pad (SA0_A). The carrier board pulls SA0_A to ground through a 4.7kΩ resistor, setting the accelerometer’s slave address to 0011000b by default. If the accelerometer’s selected slave address happens to conflict with some other device on your I²C bus, it is possible to access SA0_A through the untented via on the bottom of the board and pull it up.
In our tests of the board, we were able to communicate with the chip at clock frequencies up to 400 kHz; higher frequencies might work but were not tested. The chip itself and carrier board do not meet of some requirements to make the device compliant with I²C fast-mode. It is missing 50ns spike suppression on the clock and data lines, and additional pull-ups on the clock and data lines might also be necessary to achieve compliant signal timing characteristics.
The datasheet provides all the information you need to use this sensor, but picking out the important details can take some time. Here are some pointers for communicating with and configuring the LSM303DLM that we hope will get you up and running a little bit faster:
- The magnetometer and accelerometer are off by default. You have to turn them on by setting the correct configuration registers.
- The magnetometer will not update its data until all 6 data bytes have been read during a single I²C transfer.
- All the bytes can be read in the same transfer using the the magnetometer’s automatic subaddress updating feature (this feature is enabled by default). The accelerometer also has an automatic subaddress updating feature, if you assert the most significant bit of the subaddress.
- The accelerometer does not require you to read all of the output bytes before updating by default.
- The accelerometer and magnetometer combined in this IC are made by separate manufacturers, so there are fairly significant differences in their features, functionality, and interfaces.
- Inertial Interrupts The inertial interrupts (INT1 and INT2) are highly configurable 1.8V-level outputs that can change due to accelerations (the magnetometer has no effect on INT1 or INT2). If the sleep-to-wakeup feature of the accelerometer is enabled, when an interrupt is triggered, the accelerometer wakes up.