AN 016
Warranty Protection Using a Kionix MEMS Tri-Axis
Accelerometer
36 Thornwood Dr. - Ithaca, NY 14850
tel: 607-257-1080 — fax: 607-257-1146
www.kionix.com — info@kionix.com
© Kionix 2015
9 July 2015
Page 1 of 4
Introduction
This application note describes how to use a Kionix MEMS tri-axis accelerometer as
part of a warranty protection system. The system will record free-fall events or
high-g events which might void warranty agreements. It can be integrated into a
hand-held or portable electronic device or be used as an external module (in a
shipping container, for example).
Potential Warranty Protection System
Potentially, a warranty protection system can be created if the Kionix tri-axis
accelerometer is integrated into a device with a micro-controller, flash memory,
real time clock, and external serial communication (Figure 1).
Kionix
Tri-Axis
Accelerometer
MCU
Flash
Memory
X
Y
Z
Date/Time
External Serial
Communication
A/D
Clock
Acceleration
Figure 1: Warranty Protection System Block Diagram
In this application, a continuous 2-second buffer of the accelerometer outputs can
monitor the device, sampling at a low frequency to conserve power. If the
accelerometer senses that the total acceleration has changed from the normal static
1g of acceleration, the device must be moving. The accelerometer starts sampling
at a higher frequency and looks for preset event indicators such as accelerations
below a low acceleration (free-fall) threshold or above a high acceleration
threshold. Once an event or threshold crossing is detected, the previous 2 seconds
worth of buffered data, plus an additional amount of follow on data, perhaps 6-
seconds worth, can be permanently stored in memory with a date/time stamp.
Therefore, documenting the entire event. This documented data can then be
retrieved at a later date via serial communication and analyzed. After the event is
recorded, the acceleration is compared to the thresholds to verify that the event is
over. If it is, the accelerometer returns to sampling the acceleration. Please see
the flowchart in Figure 2 below.
AN 016
© Kionix 2015
9 July 2015
Page 2 of 4
Figure 2: Warranty protection flowchart
Now that an event history of the device has been created, if it is returned to the
manufacturer for repair, the stored event signatures can help determine if the
device was subjected to shock events that could potentially void the warranty.
As an example of such an event, Kionix performed drop tests and logged the total
acceleration data for the entire event. The acceleration was plotted over time in
order to observe the signature shown in Figure 3 below. For this calculation, the
total time in free-fall was considered to be the interval of time between the point at
which the object crossed .5g on the way to free-fall to the point at which the object
again crossed .5g upon impact.
Continuous 2 second buffer
of acceleration at low
sampling frequency
acceleration
been equal to
Continuous 2 second buffer
of acceleration at high
sampling frequency
Is the total
acceleration
above high-g
threshold or
below low-g
Store previous 2 seconds of
buffered data and 6 seconds
of follow on data to memory
No
No
Yes
Yes