Accelerometers

What is an accelerometer?

An accelerometer is an electromechanical device that measures acceleration forces such as movement or vibration.  The Actigraph accelerometers we use in PEAR Project count the number of movements you make every 10 seconds and stores these as numbers.  The numbers can tell us how much you were moving about during each 10 seconds that you were wearing the monitor.

How do accelerometers work?

The accelerometers use the piezoelectric effect – ‘piezo’ comes from the Greek word for ‘squeeze’ and this describes how they work.  Each accelerometer contains a crystal that produces a very small electrical charge when it is flexed or squeezed.  The crystal is attached to a weight and when you move, the weight wants to stay still (inertia – ask your Science teacher!).  This pulls, pushes or squeezes the crystal and it produces a charge.  The accelerometer also contains a chip and this records the movements so that we can download them later.

What data do you download?

Similar to the GPS data, the data we download from the accelerometers consists of tables of numbers.  We can put this through complicated statistics to answer some of the questions above.  It is possible to turn some of the data into graphs and we sometimes do this for posters and presentations, but we don’t do it with everybody’s data. 

Accelerometer facts

• The Nintendo Wii and Sony Playstation 3 gaming systems use accelerometers in their controllers.
• Most smart phones have accelerometers in them for gaming and for compass functions.
• IBM and Apple have recently started using accelerometers in their laptops to protect the hard drives from damage.  If you accidentally drop the laptop, the accelerometer detects the fall and switches the hard drive off.
• Accelerometers are used to activate airbags at just the right time in car crashes.