This board is a compact (0.4″ × 0.9″) breakout board for ST’s LSM303D e-compass module, a single IC featuring a 3-axis digital linear acceleration sensor and 3-axis digital magnetic sensor; we therefore recommend careful reading of the LSM303D datasheet (1MB pdf) before using this product. The LSM303D is a great IC, but its small package makes it difficult for the typical student or hobbyist to use. It also operates at voltages below 3.6 V, which can make interfacing difficult for microcontrollers operating at 5 V. This carrier board addresses these issues by incorporating additional electronics, including a 3.3 V voltage regulator and level-shifting circuits, while keeping the overall size as compact as possible. The board ships fully populated with its SMD components, including the LSM303D, as shown in the product picture.
Compared to its predecessors, including the LSM303DLM and LSM303DLHC used on our earlier LSM303 compass and accelerometer carrier boards, the LSM303D features a number of improvements, such as a wider maximum magnetic sensing range (up to ±12 gauss). Instead of appearing as two separate devices with distinct addresses like previous sensors, the LSM303D appears as a single unified I²C device, and it also offers an SPI interface for additional flexibility.
This LSM303D carrier is not pin-compatible with our earlier LSM303 compass and accelerometer carriers (the pinout and the orientation of the sensor axes are different). It should still be usable as a replacement with the appropriate wiring changes, but changes in I²C addresses and configuration registers mean that code written to interface with a different chip will need to be modified to work with an LSM303D.
The LSM303D 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. The six independent magnetic and acceleration readings (sometimes called 6DOF) are available through a digital interface, which can be configured to operate in either I²C (TWI) or SPI mode; this data 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 (1MB pdf) that explains the details of making one, and an Arduino library containing an example application can be found in the Sample Code section below.)
The carrier board includes a low-dropout linear voltage regulator that provides the 3.3 V required by the LSM303D, which allows the sensor to be powered from a 2.5–5.5 V supply. The regulator output is available on the VDD pin and can supply almost 150 mA 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 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 v3 and AltIMU-10 v4 inertial measurement units combine this LSM303D with an L3GD20H 3-axis gyro on a single board, providing nine independent readings that can be used to calculate an absolute orientation. The AltIMU-10 v4 also includes an LPS25H pressure sensor that can be used to calculate altitude.
- Dimensions: 0.4″ × 0.9″ × 0.1″ (10 × 23 × 3 mm)
- Weight without header pins: 0.6 g (0.02 oz)
- Operating voltage: 2.5 V to 5.5 V
- Supply current: 5 mA
- Output format (I²C/SPI):
- Accelerometer: one 16-bit reading per axis
- Magnetometer: one 16-bit reading per axis
- Sensitivity range (configurable):
- Accelerometer: ±2, ±4, ±6, ±8, or ±16 g
- Magnetometer: ±2, ±4, ±8, or ±12 gauss
A 1×9 strip of 0.1″ header pins and a 1×9 strip of 0.1″ right-angle header pins are included, as shown in the picture below. You can solder the header strip of your choice to the board for use with custom cables or solderless breadboards, or you can solder wires directly to the board itself for more compact installations.
The board has one mounting hole that works with #2 and M2 screws (not included).
Using the LSM303D
Regardless of the interface being used to communicate with the LSM303D, its VIN pin should be connected to a 2.5 V to 5.5 V source, and GND should be connected to 0 volts. (Alternatively, if you are using the board with a 3.3 V system, you can leave VIN disconnected and bypass the built-in regulator by connecting 3.3 V directly to VDD.)
A minimum of two logic connections are necessary to use the LSM303D in I²C mode (this is the default mode): SCL and SDA. These pins are connected to built-in level-shifters that make them safe to use at voltages over 3.3 V; they should be connected to an I²C bus operating at the same logic level as VIN. The remaining pins are connected to level-shifters on the board and are 5V-tolerant, but our 4-channel bidirectional logic level shifter can be used externally with those pins to achieve the same effect.
To use the LSM303D in SPI mode, four logic connections are typically used: SPC, SDI, SDO, and CS. These should be connected to an SPI bus operating at the same logic level as VIN. The SPI interface operates in 4-wire mode by default, with SDI and SDO on separate pins, but it can be configured to use 3-wire mode so that SDO shares a pin with SDI.
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