Advanced Sports Timer

Transcription

1 Advanced Sports Timer ECE 445 Final Paper Patrick Tchassem Noukimi Cristian Velazquez Santiago Gutierrez Group 63 TA: Yuchen He May 3, 2017

2 Abstract This document discusses the design and implementation of a multipurpose sports timer and the problem associated with monitoring the time of multiple track athletes. It demonstrates how we took different technical approaches in the aim of solving the problem while being cost effective. In an attempt of solving the problem, we designed a system that would record athlete s time and pulse, then transmit wirelessly to the coach phone. This paper also includes the requirements and verification necessary to successfully detect any discrepancy in our results. In the road of successfully accomplishing our objectives, we learned about the difficulties in implementation due to differences in theoretical calculations and error in parts from tolerances as well as difficulties in tying the different modules together. Lastly, this paper discusses the ethical and safety concerns that were taken into account during the entire process of completing this project and future work. 2

3 Contents 1 Introduction Objectives Problem Features Design Overall Block Description Power Module Charging Unit Battery Voltage Regulator Control Module Interface Module LCD Display Heartbeat Sensor Buttons Wireless Module Design Verification Power Module Control Interface Wireless Software Cost 17 5 Conclusion Accomplishment Future Work and Uncertainties

4 1 Introduction 1.1 Objectives The objective of this project is to allow a track coach to monitor the performances of different athletes in a team at the same time. The problem came from the current process of monitoring athletes performances, which requires sprinters and runners break form to pause and look at their times, and have to orally or manually write down their times for the coach to evaluate and consider. We proposed a solution that could annihilate the different problems encountered in the current process by using a design similar to a stopwatch that can be easily and discreetly worn on the multiple fingers, without impeding their form when running. The device will be able to accurately record athletes time and heartbeat as they run around a track, logging and saving their data on the device s memory each time the lap button is pressed. The device will be able to, wirelessly transmit the results to a phone, using near-field communication (NFC). 1.2 Problem The idea for the project came from a track coach from Rhode Island who was not satisfied with the current stopwatch timers on the market. The coach proposed the idea of being able to view multiple athletes times as they run around the track. He thought about a device that will be comfortable in the athlete s hand, as well as allowing them to conveniently track their times without a change in gait, and more importantly, to be able to record data without interrupting practice. Those data will be saved onto the device s memory and then sent through Near-Field communication to the coach s phone. There are many stopwatches currently on the market, most of them do not have the number of modes that we are looking to implement (such as lap interval timer, countdown timer, interval exercise timer, just to name the few.), and none of them allow the transmission of the data wirelessly to a phone where the data are viewed neatly in graphical form or table form which simplifies the training analysis. 4

5 1.3 Features Record athlete time on the a button pressed. Display athlete pulse on the LCD screen Store collected data on the micro-controller internal memory. Send data wirelessly from device to phone using NFC transmission. 2 Design Our whole system includes four mains modules: The power module, the interface module, the control module and the wireless module. They were interconnected as shown in Figure 1, which is representative of the overall system design. Figure 1: Design Block Diagram 5

6 2.1 Overall Block Description In our design, the power module is the block that processes power accordingly to every other module in the circuit. Equipped with a charging circuit, that has for purpose to charge the lithium-ion battery whenever needed, It also supplies three different voltages needed by the other modules of the system. The wireless module is the block responsible for transmitting the data stored in the microprocessor internal memory to the phone via NFC transmission. The control module, made up of just the microprocessor (STM32F030K6T6), is the block responsible for running the different instructions and computations using the internal real time clock (RTC). The interface module is the block made up of buttons, heartbeat sensor and a LCD screen. The buttons are used for different purposes and modes, while the screen is the main peripheral that displays all information needed to be read. The heartbeat sensor on the other hand, is the device responsible of recording the athlete pulse. 2.2 Power Module The power module is made up of three main sub-modules: the charging circuit, Li-ion battery, and the voltage regulator. The charger circuit is used to charge the li-ion battery once the device is connected to a USB port. The voltage regulator sub-module is made up of two DC-DC Buck converters and a DC-DC Boost converter, responsible, respectively to output from the steady 3.7 V battery voltage,1.8 ± 5%V, 3.3 ± 5%V, and 5 ± 5%V with respective maximum current of 100mA, 100mA, and 200mA. Figure 2 shows the circuit schematic of the power module, while Figure 3 shows the actual hardware product of the power module. 6

7 Figure 2: Power Module Schematic Figure 3: Power Module Board 7

8 2.2.1 Charging Unit The li-ion charger circuit utilizes the micro-usb port in order to charge the li-ion battery when it no longer contains charge. The charging circuit incorporates the integrated circuit MAX1555EZK- T from Maxim Integrated that can also allow, when charging the battery to power the device [1]. In our design, we added an LED that light up as soon as the device is connected to a USB port and go off as soon as the battery is fully charged. The mains purpose of the LED are the logic to give the battery level charge and the protection against excess charge of the battery Battery For our design, we used a 3.7V, 2000mAh li-ion battery. The battery provides power only when the on-switch is turned on. Once discharged, the battery is be charged using a micro-usb cable for another cycle of usage. The battery used in our device is rated to last more than 400 cycles of charge [2]. We ensured the protection of the battery against short circuit damages by providing a good and safe soldering on the PCB. The maximum over charge voltage of the battery is 4.2V [2] Voltage Regulator As mentioned earlier, the voltage regulator module is made of one Boost converter NCP1402, from ON Semiconductor, with internal switching frequency. It purpose is to step up the nominal 3.7V from the battery to 5V, which is the voltage required by the LCD screen display. The module is also constituted of two Buck converters MAX and MAX , also with internal switching frequencies, both from Maxim integrated, that respectively regulate the input voltage from the battery to 3.3V, needed by the micro-controller and the wireless module, and to 1.8V needed by the heartbeat sensor in the interface module. The different data-sheet helped us determinate the values of different components needed in the typical schematic application. For instance, the NCP1402 data-sheet provided us formula to calculates the components value depending of the minimum input voltage and the output voltage needed. Equation (1) allowed us to have the value of the maximum inductance needed, knowing that the maximum output current is 200mA and M equivalent to [3]. Equation (2) helped us find the value of the output capacitor when the input capacitor is set at 10µF and K1 is equivalent to [3]. 8

9 V 2 in-min L = M( ) L = ( ) = 48µH (1) V out I out-max C out = K 1 ( C in V 2 out ) C out = ( ) = 68µF (2) V in-min 3.2 We followed the same process in finding the externals parameters values for the two bucks converters used. As mentioned earlier we followed the data-sheet, used the given formula as well as their typical operating circuit, depending of the input- output power we wanted. 2.3 Control Module The control module is solely governed by the micro-controller STM32F030K6T6 from ST Electronics. It takes care of all the communication going on between the interface module and the wireless module. The control module is also the responsible for all the calculations and data storage in our design. The micro-controller is incorporated with 4kB of Random Access Memory (RAM), and 32kB of flash memory that were supposed to be used to store the data to be transmitted. Figure 4 below shows the schematic connection between the remaining modules of our design. The micro-controller used in the control module runs at 48MHz as seen in its data-sheet [4]. It sends the logged data to the NFC chip RF430CL330HCPWR from Texas Instruments, for wireless transmission using NFC to a phone. The protocol used to communicate between the control module and the wireless module is the serial peripheral interface bus commonly called SP I. The micro-controller also takes inputs from the buttons and performs the appropriate operations, such as stopping the timer when the stop button is pressed, or recording a lap time just to name the few. The LCD screen display communicates with the microprocessor in order to display the time, heartbeat, and the mode of the device. The LCD screen uses its own simple 4-bit protocol to communicate back and forth with the micro-controller [5]. The later also communicates with the heartbeat sensor in the interface module using I 2 C protocol. The heartbeat sensor is convenient in offering feedback to the athlete. 9

10 Figure 4: Control Module, Wireless Module and Interface Module Schematic 2.4 Interface Module The interface module serves as the communication canal between the user and the device. It contains the buttons, which are the mains user input, the LCD display, which serves as tool or a mean to obtain feedback from the device. It also contains the heartbeat sensor, which is mainly needed to obtain the athlete pulse. The different sub-modules of the interface module can be seen on the Figure 4 above. However, we did not include the buttons in the dotted area of the interface module because they were all over the place in our schematic LCD Display The LCD display is a simple 16x2 character display with SP I communication protocol as previously mentioned earlier. The display is responsible for exhibiting the time, mode, and the heartbeat of the user wearing the device. The LCD had to only be able to display text easily and fast. In order to make sure that it was working correctly we printed out several different tests, all passed easily. 10

11 2.4.2 Heartbeat Sensor The heartbeat sensor we used is MAX30100EFD from Maxim Integrated. The sensor has a resolution between 50 sample per second and 1000 sample per second, so this was more than sufficient to measure our users heart rate in real time. It operates at a voltages between 2.2V and 3.3V and draws at typical operation 20mA of current. Its total power dissipation is 44 mw h [8]. The interfacing with the processor will involve reading and writing to a FIFO on the sensor. The FIFO in the sensor contains raw analog data that was sampled, in order to extract the beats per minute, one would need to pass the data first through a low-pass filter, then through another filter that accentuates the peaks. Once the filtering is done, there must be an algorithm made to count the peaks within a certain time slice, and extrapolate the beats per minute from there Buttons The six buttons on our board were responsible for interacting with the athlete or user. The buttons controlled the stop start of the timer, reset for the whole board, mode selection, and other buttons for different mode interaction. For example, mode two was a countdown timer. We incorporated two extra buttons in order to increment or decrement the timer by 30 second intervals. The buttons were debounced in order to mitigate any glitches caused by the mechanical buttons. This is vital since we don t want to press a button to start the clock and then immediately stop due to a mechanical bounce. Once we added the debouncer circuit, shown in Figure 5, the interrupts to the microprocessor worked perfectly and efficiently without any errors. The simple debouncer circuit uses a 68.3kΩ resistor in series with a 100nF capacitor. 11

12 Figure 5: Debouncer Circuit 2.5 Wireless Module The wireless module consisted of the RF430CL330H Texas Instruments chip. The chip uses NFC transmission in order to send data to a phone wirelessly. The wireless module was responsible for communicating with the MPU. The MPU collects data from its running algorithms calculating the correct timing and sends the data to be stored in the RF chip s EEPROM. Data collects in the RF chip s internal memory until it is ready to be sent. Once the data is saved to the RF chip the data can finally be transferred to a phone via NFC wireless transmission. Once the data is sent to the phone, the EEPROM in the RF chip s internal memory is cleared and data is ready to be saved for another transfer. Since the chip needed an external antenna, we had to reference the data sheet to figure out how to implement its design. The first thing that was needed for the implementation of the antenna was to first figure out the intrinsic capacitance of the RF chip, C tune, shown in Figure 6. 12

13 Figure 6: RF Chip Typical Circuit Schematic After measuring three RF chips the range of the intrinsic capacitance ranged from [200, 400]nF. After measuring the internal capacitance of the RF chip, we knew that a capacitor in series would be needed. C tune would need to be 34pF in order to have an inductance between [3.57µH, 4.28µH] which is stated by the data sheet [7]. This tuned capacitor would bring down the capacitance between pins 2 and 3 in figure 6 to roughly 35pF, what we need for a resonance frequency of 13.7MHz. Using the equation from the data sheet represented by equation (3) below, we calculated the inductance value for the antenna to be around 4µH [7]. 13.7MHz = 1 LC 2π L = 1 ( π) 2 L 4µH (3) These values for the tunable capacitor and inductance aimed to make the antenna resonate at 13.7M Hz, the operating frequency for NFC transmission. 3 Design Verification We had many requirements and verification for our project. In this section we detail the ones that we had working since we were not able to verify some of our modules. we also explain the process and result of the verification testing. 13

14 3.1 Power Module The first requirement that we needed was for the charging unit to continuously provide [50mA, 100mA] of current to the battery in order to avoid any damage done to the battery. We used a digital multimeter (DMM in order to measure the current flowing between the output of the charging unit and the input to the battery. The Charging unit supplies 55.8mA of current to the battery continuously without any damage to the battery which met our requirement. The second requirement that we needed was for the battery to have a safe discharge rating of 400mA (0.2C). After measuring the current with a DMM we found that the battery has a discharge rate of roughly 300mA and never exceeded the maximum current of 400mA, thus our requirement was verified. The third requirement was that we needed to be able to provide voltage and current of5 ± 0.5V, with a maximum current of 300mA. We used a power supply increasing the input voltage from 3.2V to 4.2V in order to test the stability of the output of the voltage DC converter. The output of the NCP1402 was stable and constant shown below in Figure 7. Similarly, we applied the same test to the other two buck converters and obtained the plots shown in Figure 9 for 3.3V and Figure 9 for 1.8V which satisfy our requirements. Figure 7: 5V Sub-module Verification Plot 14

15 Figure 8: 3.3V Sub-module Verification Plot Figure 9: 1.8V Sub-module Verification Plot 3.2 Control The only requirement that we had from the control unit was that it had to communicate with the LCD screen and be able to write characters to display. We read and analyzed the data sheet for the LCD screen and figured out how to read and write to the screen. Figure 10 shows that we were able to not only write to the display but as well display the correct or wanted characters, such as mode and time data. 15

16 Figure 10: LCD Screen Verification 3.3 Interface The LCD screen must be able to display the time correctly and the unit of a second must be accurate. Clearly seen from Figure 10 above, the time was able to correctly display on the LCD screen. We accomplished this, again, by reading the data sheet for the LCD screen and coding the MPU correctly. The built-in internal timing functions from the STM32 was utilized in order to accurately keep track of the measurement of time which we verified with a phone stopwatch. The next requirement for the interface module was that it must be able to record data accurately within ± 5bpm. Since we were low in time we decided as a group to focus on the RF chip in order to get the wireless functionality for our project. Though we were unsuccessful in getting the heartbeat to work we did mess around with the sensor and learned about its functionality which is discussed above in this report. The third requirement was that the buttons needed to be active low and debounced in order to not cause any data loss or corruption. After building the debouncer circuit we tested the buttons and none of them caused any issues or errors when feeding into the MPU. The debouncer circuit worked and performed well without any glitches when viewing the signals on the oscilloscope. 16

17 3.4 Wireless The capacitance seen at pins 2 and 3 of the RF430CL330H needs to be within [31, 38]pF. The intrinsic capacitance of three of the RF430CL330H chips, using a DMM, measured to be within 200nF and 400nF. This means that the Ctune capacitance needed to be in series and about 34pF in order to have a resonance frequency of 13.7MHz. The RF430CL330H needs to transmit at a frequency of 13.7MHz. After the antenna calculation the resonant frequency should be 13.7MHz. Since we were unable to get the wireless module to work properly we were unable to verify if the transmitting frequency was 13.7MHz. Though we were not able to directly measure the frequency, the equations should still hold and we are confident that the RF430CL330H could have operated at this frequency. 3.5 Software The software was largely tested when the device was able to keep time and communicate with both the LCD and Heartbeat sensor accurately. The requirement that was needed of the software was that it must be able to correctly prioritize different interrupts. This was verified when we implemented the buttons and were able to asynchronously interact with the device while simultaneously communicating with the screen and other sensors. 4 Cost Table 1 in Appendix A shows the costs associated with all of the parts that we purchased. Though not all of the parts ordered were used in the singular device these shows well how much the raw components of the device would cost. The cost of the full device will most likely be about $ This didn t take into account the potential savings from bulk ordering of parts, or the potential cost of ordering a custom screen to make it a smaller profile. Overall we believe the device s hardware costs could be brought down to about $40. The labor costs can be estimated as follows: (3P eople ($40/h) (20h/week) 10weeks) = $36000 (4) 17

18 5 Conclusion 5.1 Accomplishment The design of the final device brought together the multiple modules that were individually tested. It made a decent, and compact stopwatch replacement that had the capability of wirelessly communicating times from an indefinite number of athletes at once. We were able to successfully keep accurate time, with splits, as well as implement a secondary countdown mode that could be used for various forms of interval training. Though the heartbeat sensor did not fully work we were able to get raw analog data from its FIFO so the calculation of the actual pulse would not be hard to implement after that. Though the wireless communication was not able to be fully finished this could be do to the SPI lines perhaps being wired incorrectly, an alternative to this would be to use the RF430 in its I 2 C configuration. This would also have the added benefit of freeing up pins if we would want more peripherals as we can use the same I 2 C lines used for the MAX The device being sponsored by a private donor means that we are ethically bound not to steal any of the ideas used here from the original inventor [6]. As well as to make sure that the battery would be safe for everyday use. We need to make sure that the case is waterproof and sweat proof so the device battery does not get damaged, since it s extremely reactive with water, and so the board do not short circuit. 5.2 Future Work and Uncertainties If we were to continue the project we would want to finish implementing the wireless module so that it would be able to communicate wirelessly to a phone. If we were to run into more problems using this chip we would probably change to a low energy consumption Bluetooth chip. Bluetooth is reliable over short distances and would probably be easier to implement into our existing design. Another thing we would improve on would be the PCB. We would want it to be smaller and more space efficient since our device is meant to be wore while an athlete trains around a track. Lastly, what we would do differently would be the addition of a better housing that would keep our PCBS, and screen dry from any form of water. This can help reduce any damage done to the circuit. Overall we were pretty happy with our design and functionality. 18

19 References [1] Spark Fun Electronics[Online] MAX pdf. [Accessed: April 2017] [2] Li-Polymer Battery Technology Specification, [Online]. Available: [Accessed: April 2017]. [3] ON Semiconductor, [Online]. Available: D.PDF [Accessed: April 2017]. [4] ST Electronics STM32F030x4/x6/x8/xC DataSheet, [Online]. Available: [Accessed: April 2017]. [5] Hitachi HD DataSheet, [Online]. Available: [Accessed: April 2017] [6] IEEE Code of Ethics, 2017.[Online]. Available: [Accessed: May 2017]. [7] Texas Instruments RF30CL330H DataSheet, [Online]. Available: [Accessed: April 2017]. [8] Maxim Integrated Pulse Oximeter and Heart-Rate Sensor IC for Wearable Health, [Online]. Available: [Accessed: April 2017]. 19

20 Appendix A 20

21 Table 1: Part List and Cost Description Price Qty Total Boost Converter With Adjustable Voltage Buck Converter With Adjustable Voltage Buck Converter With fixed Voltage USB Adapter 1-Cell Battery Charger CONN USB MICRO B RECPT SMT R/A Lithium Ion Battery - 3.7V 2000mAh uF Ceramic Capacitor X7R uF Ceramic Capacitor X7R uF 10 V ceramic Capacitor X7R uf Capacitor uf Capacitor uF 10V capacitor 10000pF 16 V Capacitor pF Capacitor uF 6.3V Capacitor uF 16V Tantalum Capacitor uF 25V 530 mohm ESR Tantalum Capacitor A 20V rectifying Diode LED Ohm Resistor k Ohms Resistor K Ohm Resistor k Ohm Resistor k Ohm Resistor k Ohm Resistor uH 1.1 A Inductor uH 1.1 A Inductor uH 900mA A Inductor IC MCU 32BIT 32KB FLASH 32LQFP Dot matrix liquid crystal display IC SENSOR OXIMETER/HEARTRATE push buttons switch Logic Gates Hex 2-Input NAND Driver IC NFC DYNAMIC TAG TARG 14-TSSOP FIXED IND 3.9UH 260MA 3.6 OHM Total $