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

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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

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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.

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