Introduction

An accelerometer is a device that measures acceleration. Acceleration is itself a measure of how an object’s velocity changes. Velocity describes an object’s current speed in a particular direction. For example, you could describe the velocity of a car as “headed north at 50 mph”.

Acceleration is a measure of the rate at which the car’s speed and/or direction changes. In all these cases an acceleration occurs:

• Direction change: The car speed continues at 50 mph, yet the car turns to travel in a northeast direction
• Speed change: The car speed changes to 45 mph and the car continues heading north
• Speed and direction change: The car speed changes to 65 mph and the car turns to travel in a northeast direction

Acceleration is a measure of the rate of these changes over time.

Note that whether the car speeds up or slows down, an acceleration occurs. Acceleration doesn’t only happen when something speeds up!

You measure acceleration with the milli-g, which is 1/1000 of a g. A g is as much acceleration as you get from Earth’s gravity.

The micro:bit measures the acceleration value (milli g-force) in one of three dimensions or the combined force in all directions (x, y, and z).

When the micro:bit is flat on a table with the screen pointing up, the gravity force is aligned with the Z axis of the micro:bit.

If you tilt it up and down, the force will align with the Y axis; this is how we can detect tilting! As the force along Y grows, the micro:bit is tilting more and more vertically.

Parameters

• dimension: The direction you are checking for acceleration or the total strength of force
• x: Acceleration in the left and right direction
• y: Acceleration in the forward and backward direction
• z: Acceleration in the up and down direction
• strength: the resulting strength of acceleration from all three dimensions (directions)

The micro:bit’s accelerometer also measures how fast the micro:bit is speeding up or slowing down as it moves through space.

Output

The accelerometer feature returns a number that represents the amount of acceleration.

For example: When the micro:bit is lying flat on a surface with the screen pointing up:

x is 0 y is 0 z is -1023 strength is 1023

On the back of the micro:bit, look closely in the lower left corner for the accelerometer.