LSM303D 3D Compass and Accelerometer Carrier with Voltage Regulator
The LSM303D 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 ±16 g and ±2 to ±12 gauss, are available through I²C and SPI interfaces. This LSM303 carrier board includes a 3.3 V voltage regulator and integrated level shifters that allows operation from 2.5 to 5.5 V, and the 0.1″ pin spacing makes it easy to use with standard solderless breadboards and 0.1″ perfboards.
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- Why are the accelerometer readings from my LSM303D stuck at an incorrect value?
We have noticed that the accelerometer in the LSM303D is particularly sensitive to brown-out conditions. If power is removed and the voltage on the 3.3 V power supply line falls significantly, but is not allowed to drop completely to 0 V, the accelerometer can be put into a bad state. When power is reapplied to the LSM303D, the accelerometer then returns readings on some or all axes that are large values and do not change much or at all. (We have often seen readings like -32760 and 24539.)
To prevent this problem from occurring, the voltage on the 3.3 V line must be allowed to fall to about 0 V when power is removed from the LSM303D. Depending on other loads and the amount of capacitance on the 3.3 V line, it can take up to several seconds for this to happen, meaning that you should avoid interrupting power to the LSM303D for any shorter period, and if such a short interruption does occur, you should remove power again for a longer period to allow the accelerometer to reset properly.
If the voltage takes too long to fall, you can add a resistor between 3.3 V and ground (a “bleeder resistor”) to discharge the 3.3 V line more quickly when power is removed. We suggest trying a resistor in the 1 kΩ to 10 kΩ range. (Note that a stronger bleeder resistor will cause the voltage to fall more quickly when power is removed, but it will also waste more power when the supply is present.)
The Zumo 32U4 includes a bleeder resistor on the 3.3 V line.