Radio Frequency Identification Sport Wearable Development

12860 words (51 pages) Dissertation

13th Dec 2019 Dissertation Reference this

Tags: SportsTechnology

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Contents

List of Abbreviations

Summary

1. Introduction

2. Company and the Backgrounds

3. The Problem Description

3.1 Initial situation

3.1.1 What is the Problem in the Sports Wearable System?

3.2 Objective

3.3 Description of the Assignment

3.3.1 How to fix the Sports Wearable Reader?

3.3.2 How to Improve the Sport Wearable System?

4. The Research Phase

4.1 The Research Question

4.2 Sub Question

4.3 The Research

4.3.1 How the as3993 UHF module works?

4.3.2 What are the possible causes of the problem?

4.3.3 What are the test needed to conduct to find out the cause of the problem?

4.3.4 What is the Transmission protocol between system and the server?

4.3.5 What is the communication protocol between microcontroller and sub modules?

4.3.6 What are the requirements for the power module?

4.4 Hypothesis

4.4.1 Design Method

5. Trouble-shooting

6. Concept/module Selection

6.1 Transmission protocol

6.2 Accelerometer/compass module

6.3 RFID Reader

6.4 Communication protocol

6.5 Battery

6.6 Battery Charger

6.7 Buck-Boost

7. Technical Description

7.1 System Overview

7.2 Module Design Description

7.2.1 Microcontroller

7.2.2 Accelerometer/compass (LSM303D)

7.2.3 Wi-Fi module RN1810

7.2.4 RF reader module NUR-05WL2

7.2.5 Battery Charger

7.2.6 Buck-Boost Controller

7.2.7 PCB Design

8. Conclusion and Recommendation

9. Attachment

8.1 ASM diagram and Code for battery charging circuit

8.2 Test plan

8.3 Component list

List of Figures

References

List of Abbreviations

RFID   Radio Frequency Identification

RFIDSW  Radio Frequency Identification Sports Wearable

Wi-Fi    Wireless Fidelity

PCB   Printed Circuit Board

PSU   Power Supply Unit

Li-Ion   Lithium Ion

GPRS   General Packet Radio Service

GSM   Global System for Mobile

VIA    Vertical interconnect access

PCM   protection circuit module

TSN   The Surface Network

Summary

RFID sport wearable is a sport device developed by The Surface Network. This device will be use to observe players movement on the sports ground as a live stream. This device will be positioned in the shin of all the player in a team. This device will count the foot step, Air time especially during the jump, foot angle and foot position in the field. All this details will be live telecast in a screen for the coach.  Using all these details, the coach will be able to plan strategic movement for the players, identify the mistake of movement, identify a player’s best skill movement and can teach that to other.

The current RFID sport wearable prototype device develop by The Surface Network contain a eCompass module which include accelerometer and magnetometer, wireless ISM transceiver communication module, a self-developed UHF Rfid Reader using As3993 chip, UHF Antenna and UHF 2 to 1 analogue Multiplexer for the antenna.  The current RFID sport wearable prototype is not fully functional. There were issues founds on two modules which are the Communication module and RFID Reader.

The goal of this project is to realize the issues in the prototype developed by the surface network and develop better version of current RFID sport wearable which also need to be small in size of a matchbox. The problem in the communication module is, it doesn’t have anti-collision feature, so when two wearables sending the data packaging, only one is sent to the backhand and the other packing collide and dropped. This issue can be solved by changing the communication module that has an anti-collision feature. The second problem is The RFID reader only has carrier signal and the sidebands are went missing.

After several test on the RFID reader such as Schematic test, RFID PCB design rule checking, RF impedance calculation, short circuit testing and signal continuity test. The problem was found in the directional coupler component has missing one pin and that cause the issue in the system and also after so many soldering and de-soldering, the internal layer of 4 layer PCB board is damaged.  Once new board is soldered, everything started to work fine.

The newly designed RFIDSW device is a betterment of the previous device. This device contain the same eCompass module for read the footstep, angle of the footstep and calculate the air time. For the communication for transmitting the data to the backhand, Wi-Fi module is use because it is fast enough to transmit the data before the next data come to the queue and also multiple data from many devices can be sent at a time.

To identify the foot position, RFID Reading module NUR-05wl2 which contain the same AS3993 chip is used. This module is integrated reading RFID module which also very small in size that helped to achieve the goal of the assignment to make it as small as matchbox size. To power up the device, 3.7V Lithium Ion Battery is used. Batteries will never supply constant voltage, voltage will drop after some use. Buck-boost convertor circuit is included in this device to supply 3.5V to the device even battery voltage higher than that and also when the battery voltage drops below 3.5V as well. Fast charging circuit also implemented in this device to charge the battery by the time it goes low. Using fast charging circuit battery can be charged within 1.5 hours.

In the future the self-developed RFID reader designed by the surface network will be use in this system by replacing the NUR-05WL2. This report shows a detailed overview of the process of researching, simulating, designing and prototyping of Radio Frequency Identification Sport Wearable device.

1. Introduction

Does Sports needs strategic movement? Yes. Every sports need a strategic movement to create a successful player. With the help of technology we can easily find/form the successful movement. The RFID Sports Wearable of The Surface Network is the device that helps to find the successful movement.

The RFIDSW Device will be placed on the shin of the sports player and this device considered as a wireless sensor. Via an internet gateway the data is send to a central database and live streaming will happen to analyze the footstep, angle and position of the player’s foot movement. This device can be use by almost every sports from indoor to outdoor such as badminton, basketball, football and etc.


Figure 1: Wireless com – RFID Sports Wearable

The main goal of this project is to build a live monitoring system to help sport coaches to observe player’s foot movement during a player is jumping, running, kicking a ball, dribbling and etc. My objective for this project is to find out what’s the problem in the Existing RFID reader board for the RFIDSW device and develop all the required hardware such as Battery charger for the battery, RFID reader for reading the tags on the floor, Accelerometer and Wi-Fi module for the communication system of the device.

The company where I am performing the Internship is called Trifork [1] which is a leading full service supplier of high-quality custom-built applications and end-to-end solutions, and more specifically I am in the department of The Surface Network [2], which is the one developing the Connective Floor project.

Information about the company and the backgrounds of the project can be found in Chapter 2, followed by the description of the problem in Chapter 3. The Research phase and design method are explained in the 4th Chapter. Next chapter – 5 is about the technical description of the RFIDSW Device. Chapter 6 shows the system overview and explains in details the different modules in the system. The last Chapter is about the conclusions and the recommendations.

2. Company and the Backgrounds

Trifork is a leading full service supplier of high-quality custom-built applications (mainly software applications: Websites, Phone Applications, etc.) and end-to-end solutions. Providing a lean approach to support each phase of the project life-cycle from idea creation, development and to ongoing maintenance and support.

Trifork aims to empower their customers by providing expert advice on the optimization of business critical IT systems and cutting-edge technology. Also enabling their customers to seamlessly integrate and use these technologies, therefore bringing immediate value to their customers’ business and customers.

Trifork also delivers solutions for the educational, finance, public, healthcare, manufacturing and telecom industries. Trifork is distributed on several continents, with approx. 50 branches.

Figure 2 : Trifork World Branch Distribution

One of the domains / industries in which Trifork operates is the Healthcare, and an example of the products provided, is the custom solution provided to the client GeriMedia, who is also backed up by VU University Medical Center in Amsterdam and 3 large Dutch healthcare institutions; Aveant Utrecht, OsiraGroep Amsterdam and Evean Zaanstreek.

This custom solution is a website targeted at the care for the elderly with long-term chronic illnesses and focusing on three key areas of excellence covering solutions for Medical Practices, Electronic Health Record (Dutch: Elektronisch Patientendossier) and Training. This Company also make custom solutions to sports players’ improvement and strategic development in a game.

In addition to the domain of Healthcare & Sportscare, Trifork possess a “daughter company” called The Surface Network (TSN), which is the one charged of the developing of the Surface Network Architecture (a combination of hardware and software {both on an abstract and more “concrete” scales}) mentioned in the Introduction.

My internship is performed in the “daughter company” The Surface Network and my position in the company is as Hardware Designer, which makes me responsible of developing all the hardware used in the Sports Wearable Device, mentioned in the Introduction.

3. The Problem Description

3.1    Initial situation

The surface network already build a sports wearable which is called sports wearable Device, this Device divided into 2 separate boards,  the main board consist microcontroller, accelerometer and communication modules, debugging LED and the other one consist the AS3993 UHF RFID Module, this module will be plug into the main module in order to have the complete system .

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Figure 4 : Complete Sports Wearable

Figure 3 : Main Board

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Figure 6 : RFID Floor

Figure 5 : RFID Module

3.1.1        What is the Problem in the Sports Wearable Device?

The RFID Module should read the RFID TAG’s which placed on the floor but  the problem in this sports wearable Device is the RFID module is not reading the Tags. Although, this module made using open source Femto Reader [3] schematic provided by AMS. The cause of the reader not reading the tags is because the sidebands of the signals are missing which contain the data of the tags but still reason for the cause is still unknown.

The communication module used in the sports wearable Device is Si4432 [4]. This is the wireless ISM transceiver that can transmit and receive signal. This module is working but it’s not too helpful for the sports wearable. Due to the fact it doesn’t have anti-collision feature, when two wearables sending the data packaging, only one is sent to the backhand and the other packing will be dropped basically signal collide to each other.

3.2    Objective

The objective of this internship is to provide TSN our own hardware and software and also reduce the expenses as much as possible without reducing the quality of the final product.

To achieve this goal, the development of such a product will be divided into three major steps:

  • Troubleshoot and find out the cause of the problem of the sports wearable reader
  • To develop a new sports wearable which is “RFIDSW” device that’s fit with all the requirement which is basically improvisation of the existing product.
  • Make the RFIDSW device as small as possible that at least fit into a box size of 6c.m * 3.7c.m

These steps chosen and an agreement made between TSN and internship student. By doing these steps, we can build a prototype of the system by fixing the sports wearable and new separate RFIDSW device that can fulfill the requirements of the TSN. In future there will be a collaboration between sports wearable and the RFIDSW device.

3.3     Description of the Assignment

The assignment of this internship as mentioned above in the Objectives and Introduction, identify the problem in the current Device (Sports Wearable) and making a new complete Device which is divide into 2 sub assignments which is making RFIDSW and making it as small as possible.

3.3.1   How to fix the Sports Wearable Reader?

By using spectrum analyzer, they have realized there is no sideband appeared in the output of the reader (at the antenna session). But to narrow the problem, the measurement should be conducted all the way in the RF path. This measurement can only be done with a RF probe.

By doing so we can identify from which point the problem is starting but also there is differential RF circuit was built in this board. To measure at the differential circuit, we specifically need a RF differential probe otherwise we might burn the circuitry.

3.3.2   How to Improve the Sport Wearable Device?

One of the main module in this system is RFID Reading module, by choosing an Embedded RFID reader/writer module can easily build our own RFID Reading solution. An important issue to remark about the Sports Wearable Device is the communication system used in the device.

As mentioned in the Initial situation, too many packaging sent from multiple players sports wearable are sent at the same time are not properly transmit to the backhand. By choosing a fast transmission communication module will help to solve this issue. Which can handle multiple packaging at the same time.

By using  rechargeable batteries  can save some cost but still as we all know that batteries will go down after some usage, rechargeable batteries are not exception for it, and so we need a charger for the rechargeable batteries in this sports wearable Device.  By making as smallest as possible will make the wearable to be comfortable to be wear in the shin of the player but still making smallest as possible will only be theoretically designed and will not make it in PCB for the current moment during the internship period.

4.  The Research Phase

Three main types of research that are used during the internship: Exploratory, Explanatory and Improving. The exploratory research is used when the researcher has ascertained something and wants to understand more about it. [5][6] For this project, the exploratory type will be used to gain more knowledge about RFID, Battery Charging and programming the Arduino. The Improving research method is used to improve certain aspect of a studied phenomenon. This method used in this project for improving the size of the PCB Board. While the goal of the explanatory research is to elaborate the theory’s explanations and determine their accuracy. This method will be applied to writing the report for this project.

During the internship research is done for several reasons. The first one is to gain theoretical knowledge about Radio Frequency Identification, the Communication and power management system. All the knowledge gained from the research will help to find the best way to build a RFID Reader, communication system and power management system, based on the requirements. Massive research has to be done to be able to Read the Tags. After designing the prototype of the RFIDSW and verifying that it works, research needs to be done in order to have a proper working system. More detail of the components and price can be found in the Attachment 9.3.

The results from the research are used to design the working Device. However, component selection for the circuits are really important. These components must have good quality but also they have to be available to order them. Any delays with ordering components might cause problems with finishing the tasks on time.

Different methods will be used for the research to find relevant information. Reading books, IEEE articles, and data sheets are the most used activities during the research phase. The most common methods for finding information during the research are Fontys search engine (biep.nu), Google Scholar and the IEEE explorer.

4.1  The Research Question

How to make the RFID reader module working and How to make betterment of the Sports wearable Device into working RFIDSW Device?

From the question mentioned above, some doubts can be rise, which are:

  • Why the RFID reader module not working?
  • The signal on the RFID reader module doesn’t contain the sideband which contain the data.
  • What are the drawbacks in the Sports Wearable Device?
    • After some initial investigation on the Sports wearable device functionality, it could be observed the following problems:
    • Communication between the sports wearable and Gateway
    • Power management of the system
    • RFID reader module
    • Size of the PCB board

The previously mentioned drawbacks set the major criteria for the research although also TSN sets some specific requirements which can be used as criteria, therefore the Measurability of the research will be defined as following:

– Communication Protocols
– Power Management designs
– Reduction of cost without affecting quality
– Easy to use this product
– Environmentally friendly
– Size of the Whole system

Regarding the Attainability, in some of the previously mentioned criteria some initial ideas can be presented, like for example:

– Transmission protocol

  • GPRS 868Mhz
  • Wi-Fi

– Communication Protocols

  •      UART
  •      I2C
  •      SPI

– Power Management designs

  •  Rechargeable Battery
  • Environmentally friendly
  • Use of RoHS compliant components (ex: resistors, capacitors)

Last but not least, the Realistic and Timely part of the research. This two sections of the SMART way of research are of high importance due to fact that they will set the boundaries of the research, so for example to be able to fulfil the main research question and deliver this new product (RFIDSW) in 6 months, more reliable designs can be implemented because of the complexity in the development, debugging and testing, although taking into account that not always Complexity means expensive.

4.2  Sub Question

The formulation of the Sub-Question can be developed from previously mentioned Main Question and from the Criteria. As mentioned above, a sub-question could be:

  • How the as3993 UHF RFID module works?
  • What are the possible causes of the problem?
  • What are the test needed to conduct to find out the cause of the problem in the as3993 UHF RFID module?
  • What is the communication protocol between microcontroller and sub modules?
  • What are the requirements for the power module?
  • What is the requirements for the wireless communication module?
  • How small the device can be?

4.3  The Research

A starting point in achieving the Main Goal of this project, can be the research on the topics involved in the Sub-questions.

4.3.1   How the as3993 UHF module works?

The as3993 UHF RFID module is an integrated analog front end and protocol handling system. Two type of readers was build using as3993 chip, which is femto and fermi readers for the previous sports wearable. Femto reader use internal amplifier and fermi use external amplifier, that’s the only difference between those two readers. Now I am only focusing on how femto reader is working. Femto reader contain As3993 UHF RFID AS3993, Balun, and load line matching circuit, low pass filter, Directional coupler, antenna tuning circuit.

Radio frequency signal will be output from the as3993. For single ended signal it should be 50 ohm to deliver maximum power but output impedance from the internal amplifier will not be 50ohm, so we need a load line matching circuit. The RF path after the matching circuit still differential, therefore a 1:1 Balun is needed to transform the impedance to 50ohm single ended. The low pass filter in the design used to filter out higher order harmonic of the carrier frequency. Rf signal enter directional coupler after the low pass filter which should provide a directivity of ~22 dB. The direct port is connected to the antenna tuning circuit before the antenna itself. Digitally tunable capacitor also attached to tune the antenna from MCU via SPI interface. [3]

4.3.2   What are the possible causes of the problem?

There is few possibilities the cause the AS3993 to be not working. By listing all the possibilities for the cause of the problem will help to draw a path for the solutions. Due to the fact the Schematic is an open source material, we can skip on schematic of the device. First of all, designing PCB might look very basic but it’s not the case for the RF PCB, there is a lot of regulation need to follow for the RF PCB especially for the differential RF path. A small mistake in RF path can lead to simply not working system. Secondly choosing the proper PCB is very important even for making the RF path calculations. Last but not least, soldering component is one of the important process. In this process multiple mistakes can occur, such as short-circuit, components not soldered properly and component could be burn when solder a component for a long time.

4.3.3   What are the test needed to conduct to find out the cause of the problem?

The test need to be conduct will be determine by the possible causes that create the problem. First of all, PCB design checking is the important test should be conduct. To avoid differential problem such as impedance matching is depend on the length of the RF path, which supposed to be equal and thickness should be same. Using isolating VIAs for the RF path also important to avoid signal integration issue and also should conduct multiple more RF PCB design rule testing.

Second test need to conduct is to make sure the calculation and PCB material used is matching or not. Dielectric constant permittivity of each material is vary for every standard frequency. So by choosing correct value of permittivity for needed frequency important to calculate the impedance matching for the RF path.

Last thing to do in making PCB work is to hardware testing. Several hardware testing need to be conduct such short-circuit test, continuity test and component active test. There is few ways to do that, using multi-meter, short circuit test and continuity test can be done but using oscilloscope we can sort it down from which point to which point the data is disappearing.

4.3.4   What is the Transmission protocol between device and the server?

All the data read by the microcontroller need to be telecast live and also the data need to be stored in the database in order to have a look whenever needed. So the data need to be transmitted from the device to the server. In this part, all the transmission protocol that considered in this project will be discussed. The software engineer involved in this project and me choosing the transmission protocol for this device but they play a major role in choosing the transmission protocol, so I did research on several transmission protocol to have an idea about it.

  • GPRS[7][8][9][10][11]

The transmission protocol option take into consideration for this device is GSM/GPRS and WI-FI. GPRS is short form of General Packet Radio Service. This is basically mobile data packet oriented service on either 2G or 3G mobile communication system. GPRS can use (one or more) of the frequencies within one of the frequency bands the radio supports (850, 900, 1800, 1900 MHz) but only 900 and 1900 MHz are used in Europe. It is a non-voice wireless internet technology, which is very famous for its internet data transmission. GPRS use radio capacity to establish the data network to be used for the data transmission. GPRS is a packet based service where distribute the data packets from several different terminal in the system across multiple channels, that’s make this system much more efficient use of the bandwidth.

This have almost same access speed to a dial up modem but it allow you to connect from anywhere. As mentioned earlier, GPRS is a packet switched network whereby it only use the radio resources during sending or receiving data rather than dedicating the entire radio channel to a mobile data for a fixed period of time. Due to the fact this the shared network, phone calls and data roaming cannot happen at the same time. The figure below explained clearly how the shared network works.

Figure 7: Shared Network (Voice call vs GPRS data)

  • WI-FI [12][13][14]

Wi-Fi is known as Wireless networking or 802.11 networking whereby it cover the IEEE 802.11 technologies. The main benefit of Wi-Fi is, it is compatible with nearly all the operating systems. Wi-Fi is a popular technology that provides interconnectivity between devices by using digital communications protocol, through which gadgets can communicate with each other in a unicast or a broadcasting manner without using any wires. Wi-Fi is a technology that provide network connectivity by using radio waves. Wireless adapter is use to create hotspot – areas in the vicinity of a wireless router that are connected to the network and allow user to access internet services to establish Wi-Fi connection.

Wi-Fi communication has almost same radio as Walkie-talkie, cell phones and other devices. Based on the amount of the data on the network, Wi-Fi provide wireless connectivity to devices by emitting frequencies between 2.4 GHz to 5 GHz which is higher than the other radios. They transmit and receive radio waves, and digital bits 1s and 0s can convert into radio waves and back into 1s and 0s. Sent information is coded as pattern of electricity and magnetism, from transceiver to receiver or vice versa – both act like an antenna. The more powerful the transmitter and receiver, the further the signal can be reached.  In the figure 8, the basic of transmitting receiving signal was picturized.

Another way Wi-Fi is more sophisticated than terrestrial radio is that it uses the Internet Protocol to communicate. This language of the Internet makes Wi-Fi very resilient and very structured. Every single transmission that send and receive has that requirement for confirmation. Wi-Fi also has a number of security features.

To access the network, users must have a password for WPA2, also known as Wi-Fi Protected Access (the 2 represents the fact that this feature is in its second generation). This is where you put in your password to get onto the Wi-Fi network. There’s another security feature called Advanced Encryption Standard (better known as AES) that was developed by the U.S. government to keep data safe as it transmits from one device to the other. “Every instance of every communication that goes over Wi-Fi is exclusive in that it’s encrypted and only the two parties involved understand it

Figure 8: Transmitting and receiving of Wi-Fi

4.3.5   What is the communication protocol between microcontroller and sub modules?

Due to the fact multiple embedded modules used in the device makes multiple communication protocols to be use in the device. Programming and using multiple protocols in the system will be take care by the Software guys in the team but to have a basic knowledge on the software part of the device and to design the PCB for the device, I made some research on the communication protocols.

The communications protocols that were learned in Fontys where: USB (Universal Serial Bus), CAN (Controller Area Network), SPI (Serial Peripheral Interface), I²C (Inter-Integrated Circuit) and UART (Universal Asynchronous Receiver / Transmitter) and more particularly the ones implemented in the practical assignment / projects in Fontys are: SPI, I²C and UART. Moreover the communication protocol support by the controller which used in this device only supports SPI, I²C and UART only. Therefore the research narrows in those 3 major Communication Protocols.

  • SPI (Serial Peripheral Interface) [15][16][17][18]

The Serial Peripheral Interface (SPI) bus is a synchronous serial communication interface specification used for short distance communication, primarily in embedded systems. The full-duplex capability makes SPI very simple and efficient for single master/single slave applications. Some devices use the full-duplex mode to implement an efficient, swift data stream for applications such as digital audio, digital signal processing, or telecommunications channels, but most off-the-shelf chips stick to half-duplex request/response protocols.

SPI is used to talk to a variety of peripherals, such as:

  • Sensors: temperature, pressure, ADC, touchscreens, video game controllers
  • Control devices: audio codecs, digital potentiometers, DAC
  • Camera lenses: Canon EF lens mount
  • Communications: Ethernet, USB, USART, CAN, IEEE 802.15.4, IEEE 802.11, handheld video games
  • Memory: flash and EEPROM
  • Real-time clocks
  • LCD, sometimes even for managing image data
  • Any MMC or SD card

The SPI bus can operate with a single master device and with one or more slave devices. If a single slave device is used, the SS pin may be fixed to logic low if the slave permits it. Some slaves require a falling edge of the chip select signal to initiate an action. With multiple slave devices, an independent SS signal is required from the master for each slave device.

To begin communication, the bus master configures the clock, using a frequency supported by the slave device, typically up to a few MHz. The master then selects the slave device with a logic level 0 on the select line. If a waiting period is required, such as for analog-to-digital conversion, the master must wait for at least that period of time before issuing clock cycles.

During each SPI clock cycle, a full duplex data transmission occurs. The master sends a bit on the MOSI line and the slave reads it, while the slave sends a bit on the MISO line and the master reads it. This sequence is maintained even when only one-directional data transfer is intended.

Transmissions normally involve two shift registers of some given word size, normally consist of 8-bit words, one in the master and one in the slave; they are connected in a virtual ring topology. Data is usually shifted out with the most-significant bit first, while shifting a new least-significant bit into the same register. After that register has been shifted out, the master and slave have exchanged register values. If more data needs to be exchanged, the shift registers are reloaded and the process repeats. Transmission may continue for any number of clock cycles. When complete, the master stops toggling the clock signal, and typically deselects the slave.

Figure 9: Typical SPI bus: master and three independent slaves

Figure 10: Timing Diagram SPI full-duplex communication

I²C (Inter-Integrated Circuit) [15] [[17][18][19]

I²C (Inter-Integrated Circuit), pronounced I-squared-C, is a multi-master, multi-slave, single-ended, serial computer bus. It is typically used for attaching lower-speed peripheral ICs to processors and microcontrollers. I²C uses only two bidirectional open-drain lines, Serial Data Line (SDA) and Serial Clock Line (SCL), pulled up with resistors. Typical voltages used are +5 V or +3.3 V.

The I²C reference design has a 7-bit or a 10-bit (depending on the device used) address space. Common I²C bus speeds are the 100 kbit/s standard mode and the 10 kbit/s low-speed mode, but arbitrarily low clock frequencies are also allowed. Recent revisions of I²C can host more nodes and run at faster speeds (400 kbit/s Fast mode, 1 Mbit/s Fast mode plus or Fm+, and 3.4 Mbit/s High Speed mode). These speeds are more widely used on embedded systems than on PCs. There are also other features, such as 16-bit addressing.

Note the bit rates are quoted for the transactions between master and slave without clock stretching or other hardware overhead. Protocol overheads include a slave address and perhaps a register address within the slave device as well as per-byte ACK/NACK (acknowledge / not acknowledge) bits. Thus the actual transfer rate of user data is lower than those peak bit rates alone would imply. For example, if each interaction with a slave inefficiently allows only 1 byte of data to be transferred, the data rate will be less than half the peak bit rate.

The maximum number of nodes is limited by the address space, and also by the total bus capacitance of 400 pF, which restricts practical communication distances to a few meters.

Figure 11: Example I2C Application

The address and the data bytes are sent most significant bit first. The start bit is indicated by a high-to-low transition of SDA with SCL high; the stop bit is indicated by a low-to-high transition of SDA with SCL high. All other transitions of SDA take place with SCL low.

If the master wishes to write to the slave then it repeatedly sends a byte with the slave sending an ACK bit. (In this situation, the master is in master transmit mode and the slave is in slave receive mode.)

If the master wishes to read from the slave then it repeatedly receives a byte from the slave, the master sending an ACK bit after every byte but the last one. (In this situation, the master is in master receive mode and the slave is in slave transmit mode.)

The master then either ends transmission with a stop bit, or it may send another START bit if it wishes to retain control of the bus for another transfer (a “combined message”).

Figure 12 : Master Write Message / Master Read Message

Figure 13 : Combined Message

  • UART (Universal Asynchronous Receiver / Transmitter [15][20][21][22][23]

UART is a computer hardware device that translates data between parallel and serial forms. UARTs are commonly used in conjunction with communication standards such as TIA (formerly EIA) RS-232, RS-422 or RS-485. The universal designation indicates that the data format and transmission speeds are configurable. The electric signalling levels and methods (such as differential signalling etc.), are handled by a driver circuit external to the UART (for example: RS-485 Transceiver).

The UART takes bytes of data and transmits the individual bits in a sequential fashion. At the destination, a second UART re-assembles the bits into complete bytes. Each UART contains a shift register, which is the fundamental method of conversion between serial and parallel forms. Serial transmission of digital information (bits) through a single wire or other medium is less costly than parallel transmission through multiple wires.

Communication may be simplex (in one direction only, with no provision for the receiving device to send information back to the transmitting device), full duplex (both devices send and receive at the same time) or half duplex (devices take turns transmitting and receiving).

The idle, no data state is high-voltage, or powered. This is a historic legacy from telegraphy, in which the line is held high to show that the line and transmitter are not damaged. Each character is sent as a logic low start bit, a configurable number of data bits (usually 8, but users can choose 5 to 8 or 9 bits depending on which UART is in use), an optional parity bit if the number of bits per character chosen is not 9 bits, and one or more logic high stop bits. In most applications the least significant data bit is transmitted first, but there are exceptions. The start bit signals the receiver that a new character is coming. The next five to nine bits, depending on the code set employed, represent the character. If a parity bit is used, it would be placed after all of the data bits. The next one or two bits are always in the mark (logic high, i.e., ‘1’) condition and called the stop bit(s). They signal the receiver that the character is completed. Since the start bit is logic low (0) and the stop bit is logic high (1) there are always at least two guaranteed signal changes between characters.

Figure 14 : Data Framing UART

The transmission and reception of data occurs at the rising edge of a clock, this clock runs of data rate (also called baud rate), therefore ones a START bit is received completely, then the data will be received correctly and no data will be lost in the transmission.

Figure 15: Example of Data Rate vs. Clock Rate

4.3.6   What are the requirements for the power module?

This RFIDSW will be placed at the shin of the player. So this device cannot be powered by a power supply because too many wiring from many players can mess up the place and can tripped over and led them to fall down. Using battery to power up the device will be the wise idea. Non-rechargeable are used to power it up the previous design. In a long term, replacing non-rechargeable batteries will cost too much but this cost will be reduce if we use rechargeable battery even though initial price is higher  compare to the non-rechargeable battery.

The main advantage of using the rechargeable battery is that we can recharge the battery when it’s gets low for numerous times. To recharge the batteries we need a battery charging circuits to be include in the main device. So we can have all the necessary circuit in a same PCB. However the disadvantage for using the battery will not deliver constant output voltage depend on the charge inside the battery high or low.

When charge inside the battery reduce, the output voltage will drop as well. By the time the output voltage lower than the minimum voltage needed to run the modules, will create a massive problem which is the device will not work and higher than the needed voltage will burn the modules! To avoid this issue, I have to build a buck-boost convertor to maintain the output voltage to be consistence.

By doing research on Rechargeable battery, battery charging circuit and buck boost convertor will help to have a clear picture about fulfilling the requirements and what fits the best in the power module.

  • Rechargeable battery [24][25][26][27][28][29][30][31]

There is multiple rechargeable battery types available in the market. Several combination of electrode and electrolytes material are used, including  lead–acid, nickel Cadmium(NiCd), nickel metal hydride (NiMH), lithium ion (Li-ion), and lithium ion polymer (Li-ion polymer). Rechargeable battery comes in various sizes and shapes, ranging from as small as button cell to megawatt capacity batteries. But there is few rechargeable batteries comes as the same size and voltages as disposable batteries, which allow to interchange with them.

An electric battery is a device consisting of two or more electrochemical cells that convert stored chemical energy into electrical energy. Each cell has a positive terminal is the cathode and a negative terminal is the anode.

Rechargeable battery can be discharged and recharged multiple times; the original composition of the electrodes can be restored by reverse current, which is not true, the restoration will reach a point of almost the original state, a clear example are the batteries in mobile phones, which after a series of charging / discharging sequences the life cycle of the battery is drastically reduced.

The capacity of a battery is the amount of electric charge it can deliver at the rated voltage. The more electrode material contained in the cell the greater its capacity. A small cell has less capacity than a larger cell with the same chemistry, although they develop the same open-circuit voltage. Capacity is measured in units such as amp-hour (A·h). The rated capacity of a battery is usually expressed as the product of 20 hours multiplied by the current that a new battery can consistently supply for 20 hours at 68 °F (20 °C), while remaining above a specified terminal voltage per cell. For example, a battery rated at 100 A·h can deliver 5A over a 20-hour period at room temperature.

Using few variables we can describe the present condition of the battery. Those are State of Charge, Depth of Discharge, Terminal Voltage, Open circuit Voltage and internal resistance. State of charge usually calculated in percentage, current integration to identify the change in the battery capacity over time. Depth of Discharge also determine in percentage, a discharge to at least 80% is referred to as a deep discharge. Terminal Voltage is the voltage between battery terminal and the load. Open circuit voltage is voltage at the battery terminal when no load is connected. Finally, internal terminal is resistance in between the battery, it vary during discharge, charging process and dependent on the battery state of charge as well.

The higher the discharge rate, the lower the capacity. The relationship between current, discharge time and capacity for a lead acid battery is approximated (over a typical range of current values) by Peukert’s law:

t = frac {Q_P} {I^k}

Figure 16: Formula Peukert’s law

Q_P is the capacity when discharged at a rate of 1 amp.

I is the current drawn from battery (A).

t is the amount of time (in hours) that a battery can sustain.

k is a constant around 1.3.

Batteries that are stored for a long period or that are discharged at a small fraction of the capacity lose capacity due to the presence of generally irreversible side reactions that consume charge carriers without producing current. This phenomenon is known as internal self-discharge. Further, when batteries are recharged, additional side reactions can occur, reducing capacity for subsequent discharges. After enough recharges, in essence all capacity is lost and the battery stops producing power, thus in other words, rechargeable batteries will end being forced to be replaced after a certain amount of time. Also other conditions that directly affect the battery lifetime are: Environmental Conditions (temperature, humidity), Overcharging, Charge / Discharge speeds, Corrosion, etc.

DOD vs Life

Figure 17: Example Depth of Discharge vs Cycle Life

Figure 18: Example Cycle Life at Various Charge / Discharge Rate

The C-rate is a measure of the rate at which a battery is being discharged. It is defined as the discharge current divided by the theoretical current draw under which the battery would deliver its nominal rated capacity in one hour. A 1C discharge rate would deliver the battery’s rated capacity in 1 hour. A 2C discharge rate means it will discharge twice as fast (30 minutes). A 1C discharge rate on a 1.6 Ah battery means a discharge current of 1.6 A. A 2C rate would mean a discharge current of 3.2 A. Standards for rechargeable batteries generally rate the capacity over a 4 hour, 8 hour or longer discharge time. Because of internal resistance loss and the chemical processes inside the cells, a battery rarely delivers nameplate rated capacity in only one hour. Types intended for special purposes, such as in a computer uninterruptible power supply (UPS). May be rated by manufacturers for discharge periods much less than one hour.

Typical discharge curves of lead acid as a function of C-rate

Figure 19: Example Discharge Time vs. Cell Voltage at various C rate

  • Battery Charging Circuit [32][33][34][35][36][37][38]

The time for charging battery is greatly variable, it depend on the item being powered as well. There is two type charging rate method, one is called fast charging and the other one is slow charging. Slow charging will safely apply the current to the battery without a need of monitoring or charge termination technique but it take a long time to charge a battery. This method also sometimes called as trickle charging. But Li-Ion will not accept the trickle charging method once the battery fully charged. Trickle charging damage the cell if it continues charging after the battery is fully charged.

Fast charging method will let the user to charge their battery within an hour but it require complex circuit to build it. Accurate battery monitoring system is required such as temperate and voltage parameters. It also should contain temperature fault, timer fault for fail safe cutoff circuit for safety reasons. To do so, a small amount of coding is needed. All these factors are the one making fast charging method as a complex system. Choosing slow or fast charging method really depend on the application’s need. Figure 18 is a comparison table which placed below to show the typical charging time for both method and various battery type although it always vary depend on battery manufacturer.

First of all, charge termination is very important in a charging circuit, charging process should be stopped immediately after the battery is fully charged. Failed to do so will increase the battery temperature which will reduce the battery life. Predetermined upper voltage limit often called as termination voltage is the cut off point for the charger to stop charging the battery, this is especially very important to fast charging method.

During the battery charging, there is 2 process happening, one is constant voltage and the other one is constant current. In the first stage, constant current charging will happen, the current depend on fast charge or slow charge but during that time the charger will deliver constant current of 100% of the battery current to charge the battery. Simultaneously the battery voltage will increase as well. Once it reach maximum battery voltage, it will start constant voltage process whereby the voltage supply to the battery will be 100% of battery voltage but the current will be start dropping until a threshold level which set by percentage of charge current typically 10% of full current of the battery. By then the battery is fully charged.

Secondly, monitoring battery temperature also a good way to determine the fault in the charging and cut off the charging immediately can prevent dangerous situation during in any chance overcharging or internal fault condition happened.  Most of the current batteries have built in PCM which is Protection circuit module or we have to build this simple PCB to avoid safety issues. The purpose of the PCM is to disable charging if any battery voltage exceed the upper threshold voltage and the charging resume once all battery voltage are below the threshold voltage. It also stop discharging when the battery voltage below the lower threshold voltage. Same goes to the ambient temperature of the battery.

Figure 20: Recharge times

  • Buck Boost [39][40][41][42]

Basically there is 3 type of switch mode power supply topologies in common use are the buck, boost and buck-boost. Buck-boost convertor is the switch mode power supply that combine the buck convertor and boost convertor in a single circuit. Buck convertor give a DC output range just lower than the input voltage and boost convertor will produce higher output voltage range than the input voltage.

There is many application use buck-boost, especially battery powered system, where supply voltage for the system vary widely, in the beginning of the full charge battery can deliver more voltage and slowly the battery voltage will start to drop down. At the full charge, the battery voltage may be higher than the desired voltage of the circuit need to be powered, using a buck convertor in such a situation will supply steadily required voltage.

Image result for buck boost designHowever as the battery charge will start dropping over a period of time where it will go below the required voltage for the circuit, at this point using a boost convertor will boost up the voltage to required level of the circuit.  By combining both buck and boost switch mode power supply designs, can handle wide range of input voltage either higher or lower than the desired voltage by the circuit. In the figure 19 below, the common component of the buck boost circuit are combined.
 In the above figure shows that how buck and boost convertors works in a single circuit. During the Tr1 is how the buck convertor works to limit the voltage when the battery voltage is higher than needed and boost convertor works during the Tr2 on which help to boost the voltage when the battery voltage is lower than the required voltage. The control unit is the one determine which convertor should react during the Tr1 and Tr2 during ON/OFF.

Figure 22: Operation as Buck during Tr1 ‘off’

Figure 25: Operation as Buck during Tr1 ‘on’

Figure 21: Buck Boost convertor combined

Figure 23: Operation as Boost during Tr2 ‘off’

Figure 24: Operation as Boost during Tr2 ‘on’

4.4  Hypothesis

The Hypothesis for this project, after conducting sufficient research is the following; different communication protocol will be needed depend on the module choosing for the sub-systems but SPI and UARTs is highly preferable compared to I2C because it is quite slow compare to other protocol and also it only use one bus for input and output. For the transmission protocol using Wi-Fi can transmit data faster than GPRS 868MHz but GPRS will be cheaper than the WIFI. So it will be worth to build two separate prototype sub-system and test practically. Choosing polymer lithium rechargeable battery will have higher advantage than using any other kind of batteries for this device. Choosing the higher capacity battery will be the best choice for the device to run for long period of time.

4.4.1   Design Method

This project is following the V-model as a design method. The method is chosen because it consists of the development of the product and doing tests at the same time. It is suitable for this project because it establishes a connection between each design step and the required test for it. An example of the V-model is shown in Figure 26. Another reason to use it is because it’s recommended for use in projects with specified and fixed requirements. [43]

Figure 26: V-model

5. Trouble-shooting

The first assignment given by company is to fix the existing sports wearable device made The Surface Network.  After the research conducted on How As3993 work, what are the possible cause of the problem and test needed to conduct to find out the cause of the problem, steps to fix the Sports wearable device is attained.

The first test conducted to find the problem is PCB Design checking. Due to the fact it is the open source schematic, the comparison made between manufacturers provided schematic with the schematic of the Sports wearable. The schematic is looks identical, so that’s not the issue.

Then the PCB design of Sports wearable device is also checked regarding PCB design rule, specific component design recommendation such as RF differential path calculation, RF impedance calculation, also isolation vias for the RF path and many more testing was conducted regarding RF PCB design. The component selection for the PCB also checked to confirm that’s not causing the issue.

The testing of RF impedance is done using polar instrument “SI8000” software to calculate the RF path. But this calculation directly connected to material used to make PCB. In this project FR4 board is used and the calculation made for permittivity provided by the manufacturer for 868MHz. After the testing done on PCB designing, there is no issues found.

The last test conducted in this PCB is Hardware testing. There were several testing to be done regarding hardware. The first hardware testing conducted is Short circuit test. The sport wearable is working but it create a band pass filter which only allow the carrier and sidebands are filtered. Which means there is no short circuit in the VCC and ground. But it’s possible short circuit in passive components such as resistor, capacitor or inductor which creates the band pass filter.

This test is conducted using multimeter and realize there is no short circuit in the circuit. The very next test conducted to narrow the issue. Which is basically tract the signal to determine from which point it lost the sidebands. To do so, RF probe is used due to the fact the RF path is differential and using normal probe can cause damage to the circuitry.

By using RF probe, missing signal is identified from which point it is happening. From the Directional coupler to the antenna there is carrier with sidebands but it is missing in the return path to the reader. So this helps to conduct the continuity test and component active test to take place from which point to which point. When the continuity test conducted from directional coupler to antenna and to microcontroller, the continuity of the signal is there but still not working as it supposed to be. So the final testing which is component active test is conducted then the smallest problem discovered which caused the big issue in the circuit. The directional coupler used in the circuit missing a pin and that IC not working in full form.

Now directional coupler in this board is changed and completely new board also soldered. The old board still not performing well. The reason for it is after so many soldering and disordering, the internal layer of the board is burned and it creates a band pass filter. Newly soldered board is worked fine and manage to read the tags.

6. Concept/module Selection

6.1 Transmission protocol

  • GPRS/GSM [7][8][9][10][11]

For the transmission protocol both Wi-Fi and GPRS/GSM are needed to be tested to make sure which one give better result. So for the GPRS/GSM, several modules was compared such as SIMCOM 800C-DS/800F/800C/800/800H. In the figure 27, the comparison between all the modules is shown. Due to the fact only sim800 and 800h has the GPRS data transfer rate up to 14.4kbps, the option is between this two modules. SIM800H is smaller than the sim800 and the basic specification for the PCB board is need to be small as possible so SIM800H is chose. In fact making a GSM module testing purpose will be waste of time, so breakout board for sim800h which is FONA is ordered for the testing.

Figure 27: GPRS Modules Comparison

  • Wi-Fi [12][13][14][44][45]

For the Wi-Fi module, the software team suggested RN171. For the testing purpose, RN-XV WiFly Module which is a breakout board from sparkfun which contain the rn171. This module used by the software engineers to test their requirements. But from the hardware perspective, RN1810 is planned to use in the system to transmit data. RN1810 is better version of rn171, such as it has integrated antenna and even though it consume higher current than rn171, it also transmit data with standard power(18dbm),higher than rn171(0dbm) which help to have a stable connection.

Solution

For the transmission protocol, Wi-Fi module is chosen instead of GPRS/GSM module after encounter issue in transmitting data to server. Data transmission from GPRS module to Internet is fast enough to transmit data to have a live stream but the problem in GPRS module is not giving the acknowledgement fast enough is indicate in the figure 28, once µC sent the data to the GPRS module. This halt the whole process from performing well. For the Wi-Fi module is not required acknowledgement from the Wi-Fi module to the µC, so it has a much better performance than GPRS module.

Figure 28: GPRS module

Figure 29: Wi-Fi Module

6.2 Accelerometer/compass module

For the accelerometer/compass, sparksfun’s LSM303D breakout board is used to do all the testing in the previous device itself. So in this device LSM303D is used to design the subsystem. After the discussion with the software engineers, required communication protocol for the lsm303d is connected to the MCU right communication pin. [46] [47]

6.3 RFID Reader

In the Previous device, ams AS3993 UHF Reader Chip is used to build the complete RFID Reader. Due to some issue it didn’t worked in the previous device but it is planned to use in the device in the future after the issue been resolved. In the current device, NordicID embedded RFID module nur-05wl2 is used because this module contain the AS3993 UHF Reader. nur-05wl2 module used in the current device because the main aim for the device is to build as small as possible. By choosing this embedded RFID module the size can be dramatically reduced. Only the RF path from nur-05wl2 module to the antenna is need to be designed but the proper calculations need to be done to create 50 Ω impedance path. [48][3]

6.4 Communication protocol

For each sub-system different communication is used as per requirement from the sub-system modules. The Wi-Fi module RN1810 is using uarts interface to the host microcontroller which is 4 wires including RTS/CTS. NordicID which is the RF reader in the device is used to communicate with the microcontroller via uarts as well but only the RX and TX.  Last but not least the 3D digital linear acceleration sensor and a 3D digital magnetic sensor which is the LSM303D module has the option to use I2C and SPI. After the research as explained on the research phase, I2C has more disadvantage for this device compare to the SPI such as I2C is lower than SPI, it also draw more power even though I2C can use for greater distance, can transmit off the PCB but which not required for this device. Speed and power is very essential for this device so communication between microcontroller and lsm303d decided to be SPI communication protocol.

6.5 Battery

There is some basic requirement to choose the battery for the device. The nominal voltage needed for the device is 3.5V so minimum battery voltage should be at least 3.5V. The higher the battery capacity>2000mAH is highly recommended because it will help the device to run longer before it needs the recharge. It also need to be RoHS-Compliant due to the fact this device is a sports wearable and attached to player’s shin.  The size of the battery also shouldn’t exceed 65mm length × 40mm width. If the battery contain PCM circuit is an added advantage otherwise this circuit needed to be design as well.

After the research conduct about the rechargeable battery. There is few rechargeable battery type, nickel cadmium (NiCd), nickel metal hydride (NiMH), lithium ion (Li-ion), and lithium ion polymer (Li-ion polymer). The lithium ion polymer battery didn’t take into consideration for the device because it is only use polymer material for the electrolyte which doesn’t make much difference and 10-30% expensive than lithium ion. Lithium ion (103456A-1S-3M) is chosen for the device after the comparison made between nickel cadmium, nickel metal hydride and lithium ion because that’s the only battery type that fit all the requirement for the battery even though the battery capacity is less than the other models still it’s in the range. The comparison table is placed below to show what are the requirement is matched. [49] [50] [51]

TYPE nickel cadmium (NiCd) nickel metal hydride
(NiMH)
lithium ion (Li-ion)
Model 1 / 2D-2400 700DH 103456A-1S-3M
NOMINAL VOLTAGE >3.5V 1.2V 1.2V 3.7V
BATTERY CAPACITY 2400mAH 7000mAh 2050mAH
ROHS-COMPLIANT NO NO YES
SIZE ∅ = 33mm H= 34.50 ∅ = 33.0mm H = 60.0mm 56mm × 37mm
PCM NO NO YES

Table 1: Battery Type

6.6  Battery Charger

The battery charging modules take into consideration to charge the lithium ion polymer battery after the research done for the power modules. The two module that take into consideration is MCP73837-8 and the other one is MCP73841-3. A small comparison table is made to show clearly which module have more advantage than other one. The comparison table can be found below. After the comparison MCP73837-8 is chose for the device.  Very important keys to choose this module is written in “bold” in the Table 2. [52]

TYPE MCP73837-8 MCP73841-3
Charge type AC-DC adapter and USB port charge AC-DC adapter
Maximum Charge Current 1A (AC-DC adapter), 0.5A (USB port) 0.5A
Temperature monitor Sent info to microcontroller LED flash
Safety Timer Sent info to microcontroller LED Flash
Standby mode Sent info to microcontroller No option
System test mode Sent info to microcontroller No option
Charge complete Sent info to microcontroller Indication LED OFF

Table 2: Battery Charger modules

6.7  Buck-Boost

After the research done for the buck boost convertor, two different company’s product take into consideration. The first one is Linear Technology’s “LTC3536” and Texas Instruments “TPS63020”. The criteria’s for choosing a buck convertor is Efficiency, Output Voltage, and Output Current. TPS63020 is giving higher efficiency than the LTC3536, this is one of the important factor in a Switch mode power supply and especially battery powered device The output current also very important to consider because the device need minimum of 2A to perform well but the LTC356 only deliver 1A during battery’s minimum output voltage. TPS63020 is wise choice to be choose for the device due to the fact it has higher advantage than the other one. This clearly indicate in the table below. [53] [54]

Model LTC3536 TPS63020
Efficiency 95% 96%
Output Voltage Variable 1.8V to 5.5V Fixed 3.3V or variable 1.2V to 5.5V
Boost mode output current 500mA at 2.7V at Vin 2A at 2.7V at Vin
Buck mode output current 1A 3A

Table 3: Buck-Boost Comparison

7.    Technical Description

7.1  System Overview

5.2V

Figure 30: System Overview

7.2  Module Design Description

This section of the report is meant for describing the individual modules that compose the RFIDSW’s main PCB design.

7.2.1   Microcontroller

– Low power consumption

  • A µC for processing power and data transmission, optimized for low power consumption

The µC selected for the implementation of the RFIDSW’s is the PIC32MX120F064H [55], which fulfils the requirements for our design:

– Low Power consumption + 5V tolerant pins
– 5 UART modules + 4 SPI modules
– Up to 48 ADC inputs
– 32 bit µC
– Highly PCB friendly component (pins can be programed to perform the function that is required,              where its most comfortable + no external oscillator is required)
– High number of I/O pins (all the pins that are not used to perform the functions specified above, can be used as general I/O)

The minimum required for this µC so be able to power up and perform properly, according to the data sheet is the following:

Figure 31 : Recommended Minimum Connection

To be able to program the µC, the datasheet recommends the following layout:

Figure 32: Recommended debugging Layout

7.2.2   Accelerometer/compass (LSM303D)


220nF and 4.7uF with 200mΩ is recommended used as reservoir capacitor in this circuit to smooth the DC Voltage during the change in the direction of the current. It require low ESR value, even though it recommended 200mΩ but in this circuit the closest range is used which is 220mΩ. For the decoupling capacitor 100nF and 10uF is recommended, this used to separate one part of electric network from another for reduce the noise in the circuit. [46] [47]

Figure 33: Accelerometer/compass recommended setting

7.2.3   Wi-Fi module RN1810


The capacitor and Resistor values are followed as per module provider’s recommendation. Capacitor in this circuit used as Decoupling between powerline and ground. The resistors used to limit the current to the particular pin.  [45]

Figure 34: Recommended component configuration

7.2.4   RF reader module NUR-05WL2

Decoupling capacitors is recommended for VCC and module_En pin as an input filter but module_En pin is not connected to input filter because it was controlled by the microcontroller in our design therefore it’s not needed. Matching and filtering circuit is also used for the antenna.

Figure 35: Reader recommended setting [46]

7.2.5   Battery Charger

The recommended value for the decoupling capacitor in part 1 is 4.7uF but I used two 2.2uF capacitors which is close to 4.7uF and by placing it in parallel, ESR rate can be reduced. The capacitor placed at the Vbat pin is to ensure the loop stability when the battery disconnected. The resistors is used to control the current flow in stat1, stat2 and PG pins.

In the part 2, resistor configuration made in such a way to choose slow charging which is 0.5A or fast charging mode which is 1A. The formula provided by the manufacture is used to calculate the resistor values,

[49]

“Single Cell, Nickel Cadmium,” [Online]. Available: http://au.element14.com/dantona-industries/1-2d-2400/battery-technology-nickel-cadmium/dp/1702651.

[50]

“Nickel Metal Hydride cell,” [Online]. Available: http://uk.farnell.com/energizer/625996/battery-nimh-aaa-power-700mah/dp/8804168.

[51]

“Lithium Ion cell,” [Online]. Available: http://uk.farnell.com/bak/103456a-1s-3m/battery-lithium-ion-3-7v-2050mah/dp/2401856.

[52]

“MCP73841-3,” [Online]. Available: http://ww1.microchip.com/downloads/en/DeviceDoc/21823D.pdf.

[53]

“LTC3536,” [Online]. Available: http://cds.linear.com/docs/en/datasheet/3536fa.pdf.

[54]

“TPS63020,” [Online]. Available: http://www.ti.com/general/docs/lit/getliterature.tsp?genericPartNumber=tps63020-q1&fileType=pdf.

[55]

“PIC32,” [Online]. Available: http://ww1.microchip.com/downloads/en/DeviceDoc/60001290C.pdf. .

[56]

“MCP73831,” [Online]. Available: http://ww1.microchip.com/downloads/en/DeviceDoc/20001984g.pdf.

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