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Zumo Shield for Arduino, v1.2
This shield makes it easy to build an Arduino-controlled Zumo robot. The shield mounts onto an assembled Zumo chassis, connecting directly to the chassis’s battery terminals and motors, and the Arduino plugs into the shield, face down. This shield includes dual motor drivers, a buzzer for playing simple sounds and music, a user pushbutton, and a 3-axis accelerometer, compass, and gyroscope. The shield boosts the battery voltage to power the Arduino, and it breaks out the Arduino I/O lines, reset button, and user LED for convenient access and to accommodate additional sensors for things like obstacle and edge detection.
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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.