The LSM303AGRTR is the tape-and-reel ordering code for STMicroelectronics’ LSM303AGR accelerometer and magnetometer. The acceleration channels support tilt and motion measurements; the magnetic channels support compass-related measurements. There is no gyroscope in this part. A design requiring measured angular velocity needs a different sensing arrangement rather than treating every six-channel sensor as the same type of IMU.
Device and interface reference
| Sensing functions | Three acceleration axes plus three magnetic-field axes |
|---|---|
| Acceleration ranges | ±2, ±4, ±8 and ±16 g |
| Magnetic dynamic range | ±50 gauss |
| Package / order suffix | 12-lead LGA, 2 × 2 × 1 mm; TR denotes tape and reel |
| VDD | 1.71–3.6 V |
| Operating temperature | −40 to +85 °C |
| I²C addresses, seven-bit | Accelerometer 0x19; magnetometer 0x1E |
| FIFO | 32 levels for acceleration data; not a shared six-channel history |
Reference: ST LSM303AGR datasheet, revision 11. The ST product documentation page is the starting point for the current device resources. The two sensing blocks require separate configuration and status handling even though they share a package.
Why a responding accelerometer does not prove the compass works
Treat bring-up as two tests. First confirm the acceleration identity and data path, then confirm the magnetic identity and data path. Each has its own output settings. A host can read believable acceleration while the magnetometer remains in a power-down mode, or repeatedly consume an old magnetic sample while acceleration continues to update.
In I²C firmware, distinguish a seven-bit address from the address byte that includes the read/write bit. Feeding an already shifted value into a driver that shifts it again can produce a failed transaction that looks like a hardware fault. For SPI, follow the separate chip-select and three-wire read requirements instead of assuming a conventional independent MISO pin. ST digital-interface reference.
Plan a timestamped compass data path
A useful log contains acquisition time, acceleration, magnetic field, validity flags and the relevant configuration. Do not assume that reading both blocks in one software function makes their measurements simultaneous. The FIFO stores acceleration history; magnetic samples need their own timestamp and freshness checks.
For example, consider an application selecting 100 acceleration samples/s and 20 magnetic samples/s. Those chosen rates correspond to 10 ms and 50 ms sampling intervals. In a uniformly scheduled system, several acceleration samples therefore share the interval between two magnetic updates. The fusion code must make an explicit interpolation, hold or rejection choice. This is a sampling example, not a claim that the sensor performs synchronization automatically.
Calibrate in the assembled product
A compass reads the magnetic environment around its installation. Moving the bare board away from a motor may change the result, but it does not validate the final enclosure with its screws, speaker, battery and power wiring. Record a baseline with the product fully assembled and repeat it under representative current loads.
Separate fixed magnetic offsets from directional distortion and temporary disturbances. Calibration data should be tied to an assembly and software revision. A calibration learned with the enclosure open can become invalid when magnetic material is added. A good acceptance exercise rotates the completed product through different orientations, checks repeatability and reports invalid conditions instead of presenting a precise-looking heading when the magnetic field is disturbed.
ST documents offset handling and high-current wiring effects in the magnetometer and application-hints sections. Tilt compensation also needs acceleration that reasonably represents gravity; strong translational motion makes that assumption less reliable. This is why a compass performance target should include the expected movement and magnetic environment rather than only the sensor’s full-scale range.
A power-budget worksheet
List the accelerometer mode and rate, magnetometer mode and rate, host wake interval and interface loading separately. Their currents must be evaluated under the matching datasheet conditions. Avoid assigning one “microamp” figure to the combined device without saying which blocks are operating.
As an illustrative system budget, if the combined sensor allocation is 250 µA and a host adds 1 mA for 5 ms every 100 ms, the host contributes another 50 µA on average. The subtotal is 300 µA before regulator loss and communications. This calculation uses chosen budget values, not measured LSM303AGR consumption. Its purpose is to show why host scheduling belongs in a sensor-power discussion.
Board review and replacement checks
- Check the complete pin table, including the capacitor connection and separate interrupt signals. A generic two-interrupt sensor symbol can omit the magnetic data-ready path.
- Verify logic-supply limits and pull-up connections as well as the main rail. A working main supply does not establish legal bus levels.
- Validate field conversion, axis orientation and freshness independently. A smooth heading trace can still use swapped axes or stale data.
- For any alternative, establish whether both acceleration and magnetic sensing are present. An accelerometer-only part cannot supply the missing magnetic measurement through firmware.
Frequently asked questions
Can this part measure angular velocity? It has no gyroscope. Angular-rate requirements need to be addressed in the system architecture.
Does the TR suffix add functions? It identifies the tape-and-reel ordering format in ST’s ordering table; the sensor function remains LSM303AGR.
Selection and purchasing
Compare a proposed replacement against the complete schematic, package drawing, interface protocol, driver and measurement requirements. A shared sensor category or package outline does not establish interchangeability. Record the candidate and the test evidence in the engineering change record before substitution.
For LSM303AGRTR, send the complete ordering code, quantity, required delivery date and any packaging or documentation requirements through the WWDParts RFQ list. Price, availability and delivery terms are confirmed in the written quotation.
Manufacturer references
Technical content reviewed October 12, 2026. Worked examples are design calculations, not measurements of a customer board. Consult the manufacturer documentation index for newer revisions and applicable errata before design release.