AN1906

AN1906
Bluetooth® Low Energy Digital Pedometer Demo Design
Author:
Zhang Feng
Microchip Technology Inc.
Studies have shown that proper daily exercise can
reduce blood pressure and body mass index. Bracelettype activity trackers featuring step counting and
Bluetooth® Low Energy (BLE) are now becoming
popular as an everyday exercise measurement and
motivation tool for people wanting to improve their
physical activity and health.
The Microchip Pedometer Demo can be worn on the
wrist like a bracelet/watch. The on-board RN4020 BLE
module allows the pedometer demo to communicate
with a smartphone or tablet on which the user’s
exercise progress can be tracked. The pedometer
demo is powered by a single 3V coin lithium battery
(CR2032).
Figure 1 shows the block diagram of the pedometer
demo.
OVERVIEW
A digital pedometer is a portable electronic device that
counts each step a person takes by detecting the
motion of the person's body with an accelerometer.
This application note demonstrates the implementation
of a Bluetooth Low Energy Digital Pedometer using the
Microchip PIC16LF1718, a cost effective 8-bit
microcontroller with extreme low power (XLP), the
Microchip RN4020 Bluetooth 4.1 Low Energy Module,
and the Bosch Sensortec BMA250E digital triaxial
accelerometer.
FIGURE 1:
BLOCK DIAGRAM
8-Bit Microcontroller
PIC16LF1718
I2C
IOC
 2015 Microchip Technology Inc.
Accelerometer
Bosch BMA250E
CR2032
Lithium
Battery
VDD
Push Button
UART
RN4020 Bluetooth® 4.1
Low Energy Module
I/Os
Three digits 7-Segment
LED Display
DS00001906A-page 1
BLUETOOTH LOW ENERGY DIGITAL PEDOMETER DEMO DESIGN
THEORY OF OPERATION
Step Detection
The Microchip pedometer demo uses a Bosch 10-bit
triaxial digital accelerometer (BMA250E) to detect the
motion of the wearer. The Microchip pedometer demo
firmware running in the PIC16LF1718 microcontroller
contains a step detection algorithm library developed
by Bosch Sensortec.
A step detection function in this library is called
periodically by the user application. The microcontroller
will read the acceleration data of X/Y/Z axes from the
accelerometer via an I2C™ interface when the step
detection function is called. The step detection function
then analyzes the accumulated acceleration data and
determines the number of steps taken by using pattern
recognition.
The accumulated number of steps can be shown on the
three digit 7-Segment LED displays or a BLE
application running in a smartphone/tablet that is
paired with the RN4020 BLE module.
Bluetooth Low Energy (BLE)
Communication
The RN4020 BLE module complies with Bluetooth
Core Specification v4.1. The RN4020 supports 13
public profiles and 17 public services based on the
Generic Attribute Profile (GATT). Among supported
public profiles, four are health-device-related profiles:
heart rate monitor, health thermometer, glucose meter
and blood pressure monitor.
The RN4020 also supports a user-defined private
profile/service, which can precisely fit a user's
particular application. This demo defined a private
service for the pedometer application. All
configurations are saved in the on-board non-volatile
memory (NVM) of the RN4020, so users need to set up
the module only once.
The microcontroller activates the RN4020 when the
BLE communication is enabled by pressing the onboard push button. The RN4020 then becomes
pairable with a smartphone or tablet that supports BLE.
The microcontroller periodically sends the step number
to the RN4020 via UART interface after successful
pairing. The RN4020 then transmits the step number to
the paired smartphone or tablet, where a compatible
BLE application can be used to display the step
number.
DS00001906A-page 2
Because the Apple® HealthKit, a new feature for iOS 8,
adheres to the BLE GATT specifications, medical
devices like heart rate and blood pressure monitors,
thermometers, and glucose meters that are built with
RN4020 will be supported natively by HealthKit. That
means device manufacturers could potentially skip the
process of developing a companion application for their
product, and instead, allow HealthKit to automatically
control the device/accessory itself when it has been
paired with the RN4020 BLE module.
Human Interface
A single push button provides quick function control to
the pedometer demo via the Interrupt-On-Change
(IOC) interface.
To turn on/off the LED display, press the button and
quickly release it within 1 second.
To enable/disable BLE communication, press the
button and hold it down for more than 1 second but less
than 4 seconds.
To zero the step number, press the button and hold it
down for more than 4 seconds, then release it.
Power
The pedometer demo is powered by a single 3V coin
lithium battery (CR2032). The LED displays are
automatically turned off after 10 seconds to save
power.
The baud rate of the UART communication is set to
2400 Kbps so that the RN4020 BLE module can remain
in Deep Sleep mode when there is no UART data
communication.
If there is no motion for 16 seconds, the microcontroller
will get a no-motion interrupt from the accelerometer
via the IOC interface. When the no-motion interrupt
occurs, the microcontroller reconfigures the
accelerometer to high-g interrupt and then puts it into
Low Power Mode 1. The microcontroller next goes into
Sleep mode as well, putting the overall system into the
lowest power consumption mode.
In Low Power Mode 1, the accelerometer is periodically
switching between a sleep phase and a wake-up
phase. During the sleep phase the whole analog circuit
of the accelerometer is powered down. During the
wake-up phase, the accelerometer works normally and
the high-g interrupt function is running to determine
when to wake up from the Low Power Mode.
The accelerometer will generate a high-g interrupt to
wake up the microcontroller when the wearer's motion
is over the preset threshold for a high-acceleration
event, such as walking, picking up the pedometer, or
waving or rotating the pedometer in the air. The
pedometer then resumes normal operation after
waking up.
 2015 Microchip Technology Inc.
BLUETOOTH LOW ENERGY DIGITAL PEDOMETER DEMO DESIGN
PROGRAM FLOWCHART
Figure 2 shows the firmware process flow of the pedometer demo.
FIGURE 2:
BLOCK DIAGRAM
Start
System
Initialization
Main Loop
Sleep Routine
Step Detection Routine –
Read Accelerometer &
Calculate Step Number
Display Step Number on
Segments LED Display
 2015 Microchip Technology Inc.
Display Step Number thru
BLE Communication
DS00001906A-page 3
BLUETOOTH LOW ENERGY DIGITAL PEDOMETER DEMO DESIGN
APPENDIX A:
PEDOMETER DEMO BOARD
Figure 3 shows the front (top photo) and the back (lower photo) of the pedometer demo board.
FIGURE 3:
PEDOMETER DEMO BOARD
DS00001906A-page 4
 2015 Microchip Technology Inc.
BLUETOOTH LOW ENERGY DIGITAL PEDOMETER DEMO DESIGN
PEDOMETER DEMO BOARD SCHEMATICS
FIGURE 4:
SCHEMATICS
APPENDIX B:
BAT PW R
1 S1
3
CL-SB-12B-01T
C1
4.7uF
R15
DNP
R16
DNP
L1
DNP
6
3
R18
0R
3
2
1
GND
5
6
7
8
9
10
12
U2
5
4
R1
DNP
R2
DNP
RA0
RE3
RB4
RB5
RB6
RB7
GND
RA1
RB3
MCU
RA2
RB2
RB0
RB1
GND
VDD
RA4
RA7
RC7
GND
RC6
RA6
RC5
3
2
VDD
R9
R17
470R
470R
470R
SEG_F
SEG_G
SEG_DP
MCP1700T-3302E/TT
VSS
VI N VOUT
U3
Pow er Regulation
VDD
LDO_VI N
1
R8
GND
ICSPDAT
C2
10uF
GND
ICSPCLK
26
SEG_D
SEG_E
470R
470R
R6
25
24
470R
VDD
SEG_A
C4
16V
0.1μF
LD3
Blue
R14
330R
GND
SEG_B
SEG_C
R3
R13
330R
470R
470R
RN_TX
R4
R5
22
21
20
RN_RX
PI C_TX
18
16
SDA
17
19
15
R12
330R
23
R7
28
GND
27
GND
C7
4.7uF
RC0
RA5
RA3
U1
MCP1640T-I/CHY
DNP
VFB
VI N VOUT
EN
DIGI T_ONE
MCP1640_EN 11
INT1
INT2
W AKE_HW
W AKE_SW
DIGI T_THREE 4
PI O1
CMD/MLDP
MCLR
MCP1640_EN
GND
RC1
VDD
RC4
RC2
RC3
GND
PIC16LF1718-I/SS
23
24
GND
LD2
Red
C3
16V
0.1μF
VDD
GND
SEG_F
4
3
2
3
2
3
2
J1
DNP
RN_CTS
RN_RTS
RN_RX
LDO_VI N
PI Ck itSe rial
2
4
6
8
10
12
PI C_TX
J2
DNP
SEG G
SEG F
K
K
SEG DP
SEG C
SEG B
SEG A
Display
SEG E
SEG E
SEG G
SEG F
K
K
SEG DP
SEG C
SEG B
SEG A
SEG E
SEG G
SEG F
K
K
SEG DP
SEG C
SEG B
SEG A
LSHD-7503
SEG D
D3
LSHD-7503
SEG D
D2
LSHD-7503
SEG D
D1
1
3
5
7
9
11
PI Ck it3
MCLR
ICSPDAT
ICSPCLK
SEG_G
1
SEG_E
5
DIGI T_ONE
SEG_D
SEG_F
4
DIGI T_TW O 1
SEG_G
5
SEG_E
SEG_D
SEG_F
4
DIGI T_THREE 1
SEG_G
5
SEG_E
SEG_D
GND
RN_TX
10 SEG_A
9 SEG_B
8 SEG_C
7 SEG_DP
6 DIGI T_ONE
10 SEG_A
9 SEG_B
8 SEG_C
7 SEG_DP
GND
GND
4
3
2
1
Accelerometer
VDD
R11
10K
C5
16V
0.1μF
SCL
SDO
SDx
S C RE W
S C RE W
7
8
9
10
U5
BMA250E
CSB
GND
VDD
GNDI O
VDD
R10
10K
VDD
VDDI O
NC
S C RE W
S C RE W
SDA
VDD
GND
W ATC H BAS E
Mechanica l Ass embly P arts
S TANDO F F
S TANDO F F
S TANDO F F
10 SEG_A
S C RE W
S TANDO F F
SEG_B
9
S C RE W
SEG_DP
SEG_C
S C RE W
8
DIGI T_THREE
7
6
W R IS T S TRA P
S C RE W
6 DIGI T_TW O
11
V DD
12
SCx
IN T 2
IN T 1 5
IN T 1
IN T 2 6
2
GND
R20
470R
C8
16V
0.1μF
14
DIGI T_TW O 13
SCL
Bluetooth Module
GND
22
21
20
18 RN_RTS
19
LD1
Green
1
2
3
OFF
ON
VDD
R19
10K
GND
U4
GND
VDD
RSVD
RSVD
PI O7
RSVD
RTS/ PI O6
17
P IO 3
BT1
CR2032
3V
S2
1
2
AIO2
AIO1
AIO0
UART_TX
UART_RX
W AKE_SW
SPI /PI
/ IO
/P
GND
P IO 2
1
SW
G ND
2
VDD
GND
GND
C6
16V
0.1μF
DS00001906A-page 5
 2015 Microchip Technology Inc.
3
4
5
6
CMD/MLDP
RN4020-V/RM
GND
P IO 1
GND
GND
GND
RN_TX
RN_RX
W AKE_SW 7
CMD/MLDP 8
GND
G ND
16
G ND
9
P IO 1/S C K
ML DP _E V /PIO 2/CS
W S /PIO 3/MO S I
P IO 4/MIS O
C T S /PIO 5
W AK E _HW
10
11
12
13
R N_C T S 14
W AK E _HW15
P IO 1
P IO 2
P IO 3
BLUETOOTH LOW ENERGY DIGITAL PEDOMETER DEMO DESIGN
APPENDIX C:
WARNINGS,
RESTRICTIONS AND
DISCLAIMER
This demo is intended solely for evaluation and
development purposes. It is NOT intended for medical,
diagnostic or treatment use. Use of Microchip devices
in life support and/or safety applications is entirely at
the buyer's risk, and the buyer agrees to defend,
indemnify and hold harmless Microchip from any and
all damages, claims, suits, or expenses resulting from
such use.
DS00001906A-page 6
APPENDIX D:
REFERENCES
PIC16(L)F1717/8/9 Cost Effective 8-Bit Intelligent
Analog Flash MCU Data Sheet (DS40001740).
RN4020 Bluetooth Low Energy Module Data Sheet
(DS50002279).
RN4020 Bluetooth Low Energy Module Command
Reference User's Guide (DS70005191).
Data sheet BMA250E Digital, triaxial acceleration
sensor (BST-BMA250E-DS004-05).
 2015 Microchip Technology Inc.
Note the following details of the code protection feature on Microchip devices:
•
Microchip products meet the specification contained in their particular Microchip Data Sheet.
•
Microchip believes that its family of products is one of the most secure families of its kind on the market today, when used in the
intended manner and under normal conditions.
•
There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our
knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip’s Data
Sheets. Most likely, the person doing so is engaged in theft of intellectual property.
•
Microchip is willing to work with the customer who is concerned about the integrity of their code.
•
Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not
mean that we are guaranteeing the product as “unbreakable.”
Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our
products. Attempts to break Microchip’s code protection feature may be a violation of the Digital Millennium Copyright Act. If such acts
allow unauthorized access to your software or other copyrighted work, you may have a right to sue for relief under that Act.
Information contained in this publication regarding device
applications and the like is provided only for your convenience
and may be superseded by updates. It is your responsibility to
ensure that your application meets with your specifications.
MICROCHIP MAKES NO REPRESENTATIONS OR
WARRANTIES OF ANY KIND WHETHER EXPRESS OR
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OTHERWISE, RELATED TO THE INFORMATION,
INCLUDING BUT NOT LIMITED TO ITS CONDITION,
QUALITY, PERFORMANCE, MERCHANTABILITY OR
FITNESS FOR PURPOSE. Microchip disclaims all liability
arising from this information and its use. Use of Microchip
devices in life support and/or safety applications is entirely at
the buyer’s risk, and the buyer agrees to defend, indemnify and
hold harmless Microchip from any and all damages, claims,
suits, or expenses resulting from such use. No licenses are
conveyed, implicitly or otherwise, under any Microchip
intellectual property rights.
Trademarks
The Microchip name and logo, the Microchip logo, dsPIC,
FlashFlex, flexPWR, JukeBlox, KEELOQ, KEELOQ logo, Kleer,
LANCheck, MediaLB, MOST, MOST logo, MPLAB,
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trademarks of Microchip Technology Incorporated in the
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The Embedded Control Solutions Company and mTouch are
registered trademarks of Microchip Technology Incorporated
in the U.S.A.
Analog-for-the-Digital Age, BodyCom, chipKIT, chipKIT logo,
CodeGuard, dsPICDEM, dsPICDEM.net, ECAN, In-Circuit
Serial Programming, ICSP, Inter-Chip Connectivity, KleerNet,
KleerNet logo, MiWi, MPASM, MPF, MPLAB Certified logo,
MPLIB, MPLINK, MultiTRAK, NetDetach, Omniscient Code
Generation, PICDEM, PICDEM.net, PICkit, PICtail,
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SQTP is a service mark of Microchip Technology Incorporated
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Silicon Storage Technology is a registered trademark of
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GestIC is a registered trademarks of Microchip Technology
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All other trademarks mentioned herein are property of their
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© 2015, Microchip Technology Incorporated, Printed in the
U.S.A., All Rights Reserved.
ISBN: 978-1-63277-172-8
QUALITY MANAGEMENT SYSTEM
CERTIFIED BY DNV
== ISO/TS 16949 ==
 2015 Microchip Technology Inc.
Microchip received ISO/TS-16949:2009 certification for its worldwide
headquarters, design and wafer fabrication facilities in Chandler and
Tempe, Arizona; Gresham, Oregon and design centers in California
and India. The Company’s quality system processes and procedures
are for its PIC® MCUs and dsPIC® DSCs, KEELOQ® code hopping
devices, Serial EEPROMs, microperipherals, nonvolatile memory and
analog products. In addition, Microchip’s quality system for the design
and manufacture of development systems is ISO 9001:2000 certified.
DS00001906A-page 7
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DS00001906A-page 8
 2015 Microchip Technology Inc.
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