Main components : the 6-axis inertial module LSM6DSL or LSM6DSM, and the eCompass LSM303AH. These MEMS (Micro Electro-Mechanical Systems) are very popular with manufacturers of mobile devices, because of their precise sensors.

1. Pedometer or Step Count
Sensor
Presented by,
Abin Varghese
S3 VAES
Roll No - 1

2. Introduction
 At CES 2017 (CES is a global consumer electronics and consumer technology tradeshow
that takes place every January in Las Vegas, Nevada.), ST announced that several
smartphones were compatible with the WeRun feature found in the WeChat
messaging app.
 Main components : the 6-axis inertial module LSM6DSL or LSM6DSM, and the
eCompass LSM303AH. These MEMS (Micro Electro-Mechanical Systems) are very
popular with manufacturers of mobile devices, because of their precise sensors.
 They can also offload some computations from the main MCU, and they consume very
little energy (only 0.4 µA in low-power mode). What makes them special is that both
can also act as a pedometer, which means a device can track its user’s run or walk steps
with little impact on performance or battery life.
 To better understand how ST is able to offer such a powerful capability in the tiniest of
packages, let’s understand how the pedometer works.

3. An Step Count Sensor by ST
Source – www.st.com

4. Working
 Both LSM6DSL/M, and the LSM303AH use an accelerometer that senses movement
by measuring the changes in electrical potential.
 When a user takes a step, a free element made of silicon, and attached to an
anchor, moves in the direction sensed.
 As it is displaced, it gets closer to or further from the base structure, which impacts
their capacitance.
 This is enough to measure speed change, but also absolute wrist tilt, and relative
tilt. The data is output in digital form on a standard SPI or I2C serial bus to the
host MCU.

5. Customizing the Pedometer
 ST’s components are special because they not only sense movement, but include
special hardware units to process the data gathered by the accelerometer.
 For instance, pedometer functions have their own specific IP block. Hence, as the
MEMS detect movement, the unit processes the information using a proprietary
algorithm to determine whether it corresponds to a step or not, without ever
needing to use the resources of the host MCU.
 IP – Internal Processor not Internet Protocol

6. Source – www.st.com

7. Optimization
 The debounce steps is the minimum number of consecutive steps that must be
detected before the counter starts increasing. Without this feature, it would be
impossible to distinguish between genuine and false steps.
 For example, if a person has to stop at a crosswalk while on a run, it would be
pointless to count the movements made while waiting for the signal to change. The
debounce steps can ensure that the counter only increments when the user
resumes its pace. Engineers can also customize the minimum threshold, meaning
the minimum force that can qualify as a step. Hence, developers can create
different profiles with specific settings adjusting for various activities, to more
accurately measure steps and produce meaningful results.

8. System Optimizations
 With each detected step, the pedometer unit sends an interrupt to the step
counter. An interrupt is a signal transmitted to a specific component, usually a
host, indicating that an event requires its attention.
 In this system, the pedometer sends an interrupt using its INT1 pin (LSM6DSL
and LSM6DSM) to a particular pin on the host. As a result, the rest of the host
can be in sleep mode, or perform other tasks, while only a small part of the
architecture detects the presence of an interrupt, processes it, and decides if
waking the rest of the MCU is necessary.
 This system also ensures the synchronization of the data acquisition process to
avoid any loss of information.

9.  For instance, it is possible to send an interrupt only after exceeding the debounce
steps to ensure that the system doesn’t waste energy on trivial movements.
 As more and more users sleep with their fitness band on, it would be pointless to
waste battery life trying to measure the small and sporadic gestures that occur
while asleep. By correctly setting the system’s debounce steps and minimum
threshold, engineers ensure no interrupts wake the system up, even if the user
moves during sleep.

10. Modular Efficiency
 Including both the 6-axis inertial module, and the compass, in one mobile device, is
very common. Therefore, why did ST choose to include an accelerometer and a
specific pedometer unit in both ? The reason is that they are modular, meaning it is
possible to use them both for greater accuracy, or disable one accelerometer to
save energy, while still benefitting from a powerful step counter. This design also
allows for greater flexibility. For instance, if one of the components is already off,
the system can still count steps by relying on the pedometer IP of the
component that’s awake, no matter which one it is.

11.  In addition to supporting main OS requirements, these modules offer real, virtual
and batch sensors with up to 4 Kbytes for dynamic data batching for advanced
pedometer, timestamp, wrist tilt and many other smart functions. Specifically
designed for OIS applications, the LSM6DSM comes with a new low-noise
gyroscope and configurable filter as well as a dedicated additional processing and
and serial port that together improve camera-OIS performance. Both devices are
available in 14-lead LGA modules (2.5 x 3 x 0.83 mm) that are pin-and-
footprint compatible with LSM6DS3/H devices.

12. Reference
 http://www.leafhealthcare.com/
 http://blog.st.com/pedometer-mems-step-count/
 http://st.com/
 http://ieeexplore.ieee.org/