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AN1906Bluetooth® Low Energy Digital Pedometer Demo Design
Studies have shown that proper daily exercise canreduce blood pressure and body mass index. Bracelet-type activity trackers featuring step counting andBluetooth® Low Energy (BLE) are now becomingpopular as an everyday exercise measurement andmotivation tool for people wanting to improve theirphysical activity and health.
OVERVIEWA digital pedometer is a portable electronic device thatcounts each step a person takes by detecting themotion of the person's body with an accelerometer.This application note demonstrates the implementationof a Bluetooth Low Energy Digital Pedometer using theMicrochip PIC16LF1718, a cost effective 8-bitmicrocontroller with extreme low power (XLP), theMicrochip RN4020 Bluetooth 4.1 Low Energy Module,and the Bosch Sensortec BMA250E digital triaxialaccelerometer.
The Microchip Pedometer Demo can be worn on thewrist like a bracelet/watch. The on-board RN4020 BLEmodule allows the pedometer demo to communicatewith a smartphone or tablet on which the user’sexercise progress can be tracked. The pedometerdemo is powered by a single 3V coin lithium battery(CR2032).
Figure 1 shows the block diagram of the pedometerdemo.
FIGURE 1: BLOCK DIAGRAM
Author: Zhang FengMicrochip Technology Inc.
8-Bit Microcontroller PIC16LF1718
I2C IOC UART I/Os
Accelerometer Bosch BMA250E
Push Button
RN4020 Bluetooth® 4.1 Low Energy Module
Three digits 7-Segment LED Display
CR2032 Lithium Battery
VDD
2015 Microchip Technology Inc. DS00001906A-page 1
BLUETOOTH LOW ENERGY DIGITAL PEDOMETER DEMO DESIGN
THEORY OF OPERATION
Step DetectionThe Microchip pedometer demo uses a Bosch 10-bittriaxial digital accelerometer (BMA250E) to detect themotion of the wearer. The Microchip pedometer demofirmware running in the PIC16LF1718 microcontrollercontains a step detection algorithm library developedby Bosch Sensortec.
A step detection function in this library is calledperiodically by the user application. The microcontrollerwill read the acceleration data of X/Y/Z axes from theaccelerometer via an I2C™ interface when the stepdetection function is called. The step detection functionthen analyzes the accumulated acceleration data anddetermines the number of steps taken by using patternrecognition.
The accumulated number of steps can be shown on thethree digit 7-Segment LED displays or a BLEapplication running in a smartphone/tablet that ispaired with the RN4020 BLE module.
Bluetooth Low Energy (BLE) CommunicationThe RN4020 BLE module complies with BluetoothCore Specification v4.1. The RN4020 supports 13public profiles and 17 public services based on theGeneric Attribute Profile (GATT). Among supportedpublic profiles, four are health-device-related profiles:heart rate monitor, health thermometer, glucose meterand blood pressure monitor.
The RN4020 also supports a user-defined privateprofile/service, which can precisely fit a user'sparticular application. This demo defined a privateservice for the pedometer application. Allconfigurations are saved in the on-board non-volatilememory (NVM) of the RN4020, so users need to set upthe module only once.
The microcontroller activates the RN4020 when theBLE communication is enabled by pressing the on-board push button. The RN4020 then becomespairable with a smartphone or tablet that supports BLE.The microcontroller periodically sends the step numberto the RN4020 via UART interface after successfulpairing. The RN4020 then transmits the step number tothe paired smartphone or tablet, where a compatibleBLE application can be used to display the stepnumber.
Because the Apple® HealthKit, a new feature for iOS 8,adheres to the BLE GATT specifications, medicaldevices like heart rate and blood pressure monitors,thermometers, and glucose meters that are built withRN4020 will be supported natively by HealthKit. Thatmeans device manufacturers could potentially skip theprocess of developing a companion application for theirproduct, and instead, allow HealthKit to automaticallycontrol the device/accessory itself when it has beenpaired with the RN4020 BLE module.
Human InterfaceA single push button provides quick function control tothe pedometer demo via the Interrupt-On-Change(IOC) interface.
To turn on/off the LED display, press the button andquickly release it within 1 second.
To enable/disable BLE communication, press thebutton and hold it down for more than 1 second but lessthan 4 seconds.
To zero the step number, press the button and hold itdown for more than 4 seconds, then release it.
PowerThe pedometer demo is powered by a single 3V coinlithium battery (CR2032). The LED displays areautomatically turned off after 10 seconds to savepower.
The baud rate of the UART communication is set to2400 Kbps so that the RN4020 BLE module can remainin Deep Sleep mode when there is no UART datacommunication.
If there is no motion for 16 seconds, the microcontrollerwill get a no-motion interrupt from the accelerometervia the IOC interface. When the no-motion interruptoccurs, the microcontroller reconfigures theaccelerometer to high-g interrupt and then puts it intoLow Power Mode 1. The microcontroller next goes intoSleep mode as well, putting the overall system into thelowest power consumption mode.
In Low Power Mode 1, the accelerometer is periodicallyswitching between a sleep phase and a wake-upphase. During the sleep phase the whole analog circuitof the accelerometer is powered down. During thewake-up phase, the accelerometer works normally andthe high-g interrupt function is running to determinewhen to wake up from the Low Power Mode.
The accelerometer will generate a high-g interrupt towake up the microcontroller when the wearer's motionis over the preset threshold for a high-accelerationevent, such as walking, picking up the pedometer, orwaving or rotating the pedometer in the air. Thepedometer then resumes normal operation afterwaking up.
DS00001906A-page 2 2015 Microchip Technology Inc.
BLUETOOTH LOW ENERGY DIGITAL PEDOMETER DEMO DESIGN
PROGRAM FLOWCHARTFigure 2 shows the firmware process flow of the pedometer demo.
FIGURE 2: BLOCK DIAGRAM
Start
System Initialization
Step Detection Routine – Read Accelerometer & Calculate Step Number
Display Step Number on Segments LED Display
Display Step Number thru BLE Communication
Main Loop
Sleep Routine
2015 Microchip Technology Inc. DS00001906A-page 3
BLUETOOTH LOW ENERGY DIGITAL PEDOMETER DEMO DESIGN
APPENDIX A: PEDOMETER DEMO BOARDFigure 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
APPENDIX B: SCHEMATICS
FIGURE 4: PEDOMETER DEMO BOARD SCHEMATICS
330RR12
330RR13
330RR14
BlueLD
3Green
LD1
RedLD
2
GN
D
VDD
GN
DCR2032BT1
MCP1640T-I/CHY
VIN6
S W 1
EN3
G ND2
VFB4
VOU
T5
U2
DNP
10uFC2
R15DNP
DNPR16
R1DNP
R2DNP
GN
DG
ND
GN
DG
ND
GN
D
3V
VDD
L1DNP
MCP1700T-3302E/TT
VIN3
VOU
T2
VSS1
U3
GN
D
VDD
GN
D
10KR10
10KR11
VDD
VDD
GN
D
GN
D
GN
D
GN
D
SDO
1
SDx
2
VDD
IO3
NC
4
IN T 15
IN T 26
VDD
7
GN
DIO
8
GN
D9
CSB10
V DD 11
S C x 12
SDO
SDx
VDD
IO
NC
IN T 1
IN T 2
VDD
GN
DIO
GN
D
CSB
V DD
S C x
BMA250E
U5
GN
DG
ND
GN
DG
ND
VDD
GN
D
K1
SEG F
2
SEG G
3
SEG E
4
SEG D
5K
6SEG
DP
7SEG
C8
SEG B
9SEG
A10
KSEGF
SEGG
SEGE
SEGD
K
SEGD
P
SEGC
SEGB
SEGA
LSHD-7503
D1K
1
SEG F
2
SEG G
3
SEG E
4
SEG D
5K
6SEG
DP
7SEG
C8
SEG B
9SEG
A10
KSEGF
SEGG
SEGE
SEGD
K
SEGD
P
SEGC
SEGB
SEGA
LSHD-7503
D2K
1
SEG F
2
SEG G
3
SEG E
4
SEG D
5K
6SEG
DP
7SEG
C8
SEG B
9SEG
A10
KSEGF
SEGG
SEGE
SEGD
K
SEGD
P
SEGC
SEGB
SEGA
LSHD-7503
D3
CL-SB-12B-01T
13
2
S1
GN
D
470RR3
470RR4
470RR5
470RR6
470RR7
470RR8
470RR9
470RR17
16V0.1μF
C4
VDD
GN
D
GN
D
GN
D
PICkit3
PICkitSe
rial
RE31
RA0
2
RA1
3
RA2
4
RA3
5
RA4
6
RA5
7
GN
D8
RA7
9
RA6
10
RC011
RC112
RC213
RC314
RC415
RC516
RC617
RC718
GN
D19
VDD
20RB0
21RB1
22RB2
23RB3
24RB4
25RB5
26RB6
27RB7
28RE3
RA0
RA1
RA2
RA3
RA4
RA5
GN
D
RA7
RA6
RC0
RC1
RC2
RC3RC4
RC5
RC6
RC7
GN
D
VDD
RB0
RB1
RB2
RB3
RB4
RB5
RB6
RB7
U1
PIC16LF1718-I/SS
ON
OFF
BAT PW
R
GN
D1
AIO2
2
AIO1
3
AIO0
4
UA
RT_TX5
UA
RT_RX6
WA
KE_SW7
CMD
/MLD
P8
G ND9
P IO 1/S C K10
ML DP _E V /PIO 2/CS11
W S /PIO 3/MO S I12
P IO 4/MIS O13
C T S /PIO 514
W AK E _HW15
G ND16
SPI/PIO17
RTS/PIO
618
PIO7
19RSVD
20RSVD
21RSVD
22VD
D23
GN
D24
GN
D
AIO2
AIO1
AIO0
UA
RT_TX
UA
RT_RX
WA
KE_SW
CMD
/MLD
P
G ND
P IO 1/S C KML DP _E V /PIO 2/CSW S /PIO 3/MO S IP IO 4/MIS OC T S /PIO 5W AK E _HW
G ND
SPI/P//IO
RTS/PIO
6
PIO7
RSVD
RSVD
RSVD
VDD
GN
D
RN4020-V/RM
U4
S2
VDD
VDD
VDD
MCP1640_EN
MCP1640_EN
MCLR
MCLR
PIO1
P IO 1P IO 2P IO 3
P IO 1
P IO 2
P IO 3
LDO
_VIN
LDO
_VIN
RN_RX
RN_RX
RN_RX
PIC_TX
PIC_TX
RN_TX
RN_TX
RN_TX
WA
KE_SW
W AK E _HW WA
KE_HW
WA
KE_SW
SDA
SCL
INT1
INT2
DIG
IT_ON
E
DIG
IT_TWO
DIG
IT_THREE
DIG
IT_THREE
DIG
IT_TWO
DIG
IT_ON
E
DIG
IT_ON
E
DIG
IT_TWO
DIG
IT_THREE
IN T 1
IN T 2
SDA
SCL
RN_CTS
ICSPDA
T
ICSPDA
TICSPCLK
ICSPCLK
SEG_A
SEG_A
SEG_A
SEG_A
SEG_B
SEG_B
SEG_B
SEG_B
SEG_C
SEG_C
SEG_C
SEG_C
SEG_D
SEG_D
SEG_D
SEG_D
SEG_E
SEG_E
SEG_E
SEG_E
SEG_F
SEG_F
SEG_F
SEG_F
SEG_G
SEG_G
SEG_G
SEG_G
SEG_D
P
SEG_D
P
SEG_D
P
SEG_D
P
0R R18
CMD
/MLD
P
CMD
/MLD
P
R N_C T S
RN_RTS
RN_RTS
16V0.1μF
C8
GN
D
470R
R20
10KR19
VDD
GN
D
4.7uFC1
4.7uFC7
16V0.1μF
C3
16V0.1μF
C5
16V0.1μF
C6
123
DNPJ2
12
34
56
78
910
1112
J1DN
P
MCU
Bluetooth Module
Power Regulation
Display
Accelerom
eter
GN
D
WR
IST S
TRAP
SC
REW
SC
REW
SC
REW
SC
REW
SC
REW
SC
REW
SC
REW
SC
REW
STA
ND
OFF
STA
ND
OFF
STA
ND
OFF
STA
ND
OFF
Mechanical Assem
bly Parts
WA
TCH
BAS
E
2015 Microchip Technology Inc. DS00001906A-page 5
BLUETOOTH LOW ENERGY DIGITAL PEDOMETER DEMO DESIGN
APPENDIX C: WARNINGS, RESTRICTIONS AND DISCLAIMER
This demo is intended solely for evaluation anddevelopment purposes. It is NOT intended for medical,diagnostic or treatment use. Use of Microchip devicesin life support and/or safety applications is entirely atthe buyer's risk, and the buyer agrees to defend,indemnify and hold harmless Microchip from any andall damages, claims, suits, or expenses resulting fromsuch use.
APPENDIX D: REFERENCESPIC16(L)F1717/8/9 Cost Effective 8-Bit IntelligentAnalog Flash MCU Data Sheet (DS40001740).
RN4020 Bluetooth Low Energy Module Data Sheet(DS50002279).
RN4020 Bluetooth Low Energy Module CommandReference User's Guide (DS70005191).
Data sheet BMA250E Digital, triaxial accelerationsensor (BST-BMA250E-DS004-05).
DS00001906A-page 6 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 ourproducts. Attempts to break Microchip’s code protection feature may be a violation of the Digital Millennium Copyright Act. If such actsallow 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 deviceapplications and the like is provided only for your convenienceand may be superseded by updates. It is your responsibility toensure that your application meets with your specifications.MICROCHIP MAKES NO REPRESENTATIONS ORWARRANTIES OF ANY KIND WHETHER EXPRESS ORIMPLIED, WRITTEN OR ORAL, STATUTORY OROTHERWISE, RELATED TO THE INFORMATION,INCLUDING BUT NOT LIMITED TO ITS CONDITION,QUALITY, PERFORMANCE, MERCHANTABILITY ORFITNESS FOR PURPOSE. Microchip disclaims all liabilityarising from this information and its use. Use of Microchipdevices in life support and/or safety applications is entirely atthe buyer’s risk, and the buyer agrees to defend, indemnify andhold harmless Microchip from any and all damages, claims,suits, or expenses resulting from such use. No licenses areconveyed, implicitly or otherwise, under any Microchipintellectual property rights.
2015 Microchip Technology Inc.
QUALITY MANAGEMENT SYSTEM CERTIFIED BY DNV
== ISO/TS 16949 ==
Trademarks
The Microchip name and logo, the Microchip logo, dsPIC, FlashFlex, flexPWR, JukeBlox, KEELOQ, KEELOQ logo, Kleer, LANCheck, MediaLB, MOST, MOST logo, MPLAB, OptoLyzer, PIC, PICSTART, PIC32 logo, RightTouch, SpyNIC, SST, SST Logo, SuperFlash and UNI/O are registered trademarks of Microchip Technology Incorporated in the U.S.A. and other countries.
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, RightTouch logo, REAL ICE, SQI, Serial Quad I/O, Total Endurance, TSHARC, USBCheck, VariSense, ViewSpan, WiperLock, Wireless DNA, and ZENA are trademarks of Microchip Technology Incorporated in the U.S.A. and other countries.
SQTP is a service mark of Microchip Technology Incorporated in the U.S.A.
Silicon Storage Technology is a registered trademark of Microchip Technology Inc. in other countries.
GestIC is a registered trademarks of Microchip Technology Germany II GmbH & Co. KG, a subsidiary of Microchip Technology Inc., in other countries.
All other trademarks mentioned herein are property of their respective companies.
© 2015, Microchip Technology Incorporated, Printed in the U.S.A., All Rights Reserved.
ISBN: 978-1-63277-172-8
Microchip received ISO/TS-16949:2009 certification for its worldwide
DS00001906A-page 7
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 8 2015 Microchip Technology Inc.
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