Full report - ECE - Cornell University
Contents
1. 8 References 1 Cornell University Courses of Study http courses cornell edu 2 Nordic Semiconductor nRF24L01 datasheet http www nordicsemi com kor content download 2726 34069 file nRF24L01P_Product Specificatio n_1 0 paf 3 Jaehyun Kim Application Programming Interface For Radiofrequency Transceiver nRF24L01 by Nordic Semiconductor and Atmel Mega644 microcontroller http people ece cornell edu land courses ece4760 StudentWork Jaehyun_Kim_jk726 index html 4 Brennan Ball nRF24L01 Tutorials http blog divembedded com 5 SparkfunTransceiver nRF24L01 Module with Chip Antenna product page http www sparkfun com products 691 6 Bruce Land ECE 4760 Sound sequencer and synthesis http people ece cornell edu land courses ece4760 labs s2012 lab3 html 27 7 Sokolov Alexey jSSC java simple serial connector https code google com p java simple serial connector 8 Bruce Land ECE 4760 Laboratory 3 Video Game Particle Beam http people ece cornell edu land courses ece4760 labs s2011 lab3 html 282. Base Station Student lt Student e 4 ss 79 O Serial connection to computer Figure 7 Structure of lab exercise 3 Student The third exercise involves students connecting to the base station wirelessly to play a multiplayer game The premise of the game is that players are space cowboys literally that need to herd cows in hermetically sealed bubbles that are floating in space into corrals Both players and cows are modeled as spherical particles and players herd the cows by elastically colliding with them Players control their movement by turning using a 10KQ trimpot and accelerating by pressing buttons on the STK500 There are also inertial effects on the player and cow particles as well as drag unlike space but it improves playability since the cows would bounce all over the place otherwise 13 amp Wireless game er Scores abct23 12 bed234 3 4 Problems Javadoc B Declaration E Console 5 Game Java Application C Program Files Java jre7 bin javaw exe May 15 2012 9 39 56 PM abc123N13 abc123B13 abc123N130 bcd234B102 bcd234N102 abc123B136 abc123N130 abc123F130 abc123N130 abc123B130 abc123N130 Figure 8 Screenshot of the game the received player commands can be seen in the console 5V 10K ATMega644 Ohm Port A0 Trimpot GND Figure 9 Connections for the trimpot 14 The m
3. The project uses modules manufactured by Sparkfun Electronics which mount the nRF24L01 a 16 MHz crystal oscillator that produces the clock for the transceiver a chip antenna and a 3 3V LDO regulator onto a 0 8x0 9 printed circuit board 5 The module is connected to the ATmega644 as shown in Appendix 1 The module is supplied with 5V through its VCC pin which is then regulated to 3 3V for the transceiver The pins for the SPI interface are connected to ports B3 to B7 on the Mega644 which are used by the integrated SPI interface of the ATmega644 The nRF24L01 supports a maximum SCK frequency of 4 MHz thus the SPI frequency of the ATmega644 is set to fosc 4 since a 16 MHz crystal is used for the ATmega644 set the nRF24L01 to use an RF data rate of 2 Mbps and the maximum RF output power of 0 dBm at which the transceiver is documented to draw 11 3 mA of current when transmitting and 13 5 mA when receiving te CE a gt S lt Figure 1 nRF24L01 connected to the STK500 along with the trimpot used for the wireless multiplayer game lab exercise Figure 2 nRF24L01 connected to the ATmega644 on the prototype board 4 2 Device Drivers for the nRF24L01 Device drivers compatible with the ATmega644 were written for the nRF24L01 The drivers support point to point and multiceiver in a star network operation with and without Enhanced Shockburst Enhanced Shockburst is a link layer like TCP built int
4. the base station The base station then plays through the 32 bytes in each packet as time passes This would result in higher throughput and thus better audio quality as it allows for a higher sample rate and scalability as less packets need to be sent compared to the current implementation Enhanced Shockburst can also be used with the 32 byte packet to fix problems with packet losses disrupting the audio playback In the current implementation packet losses sometime cause the audio to sound distorted 19 6 Conclusions The project achieved its goal of developing ATmega644 compatible device drivers for the nRF24L01 and using them to build a lab exercise for ECE 4760 By analyzing the performance of the nRF24L01 in the Digital Lab environment when used with the ATmega644 a better understanding of the capabilities and optimal use of the nRF24L01 was gained However due to equipment and manpower shortages testing for scalability could not be done with a greater number of transceivers in order to simulate actual deployment of the lab exercises wherein there may be up to 20 students groups simultaneously transmitting packets 7 Future Work Future work could involve an improved version of lab exercise 2 which would have the transmitters accumulate 32 byte sequences of values which represent the audio waveform over 32 time steps and sent them as 32 byte packets to the base station instead of current the audio waveform byte by byte in
5. unsigned long address and set_RX_addr unsigned long address unsigned char pipe In these drivers the transceiver is set to use 4 byte address which correspond to an unsigned long in the ATmega644 The RX address of each pipe is set seperately by calling set_RX_address with different values for pipe from 0 to 5 For the transmitter in TX_mode the RX address for pipe 0 should be set to the same address as the TX address in order for ACKs to be received Based on the nRF24L01 documentation it is recommended that addresses have multiple transitions between 1 and 0 bits to avoid noise being mistaken for packets define PIPE ADDRESS 0 0xb4b5b600 define PIPE ADDRESS 4 0xb4b5b604 set RX addr PIPE ADDRESS 0 0 set TX addr PIPE ADDRESS 0 set RX addr PIPE ADDRESS 4 4 23 set_RF_channel unsigned char channel can be used to change the RF channel transceivers must be set to the same channel to communicate with each other channel is a 7 bit number Using different channels for different star networks can help reduce interference SEL RE channel 8 Sending and receiving packets transmit_packet char packet is called to transmit the packet which is a byte array or string It blocks until the packet is successfully transmitted whereupon it returns 1 or the maximum number of retries is reached whereupon it returns 2 char transmission result shows whether the transmission succe
6. DESIGN A WIRELESS LAB FOR ECE4760 A Design Project Report Presented to the School of Electrical and Computer Engineering of Cornell University in Partial Fulfillment of the Requirements for the Degree of Master of Engineering Electrical and Computer Engineering Submitted by Yi Heng Lee MEng Field Advisor Bruce R Land Degree Date May 2012 Abstract Master of Engineering Program School of Electrical and Computer Engineering Cornell University Design Project Report Project Title Design a wireless lab for ECE4760 Author Yi Heng Lee Abstract In this project a wireless lab exercise is developed for the ECE4760 Digital Systems Design using Microcontrollers course The lab exercise involves the use of Nordic systems nRF24L01 transceivers for wireless communication between Atmel ATmega644 microcontrollers Device drivers compatible with the ATmega644 were written for configuring and operating the nRF24L01 Three lab exercises of increasing complexity that demonstrate the usage of the transceivers in different applications were developed Table of Contents da WO N i Executive SummarV pce leale 3 lt Design Reqguirements csrpaaarianaaalaea 4 Possible Solutions and Related work settee ee eeennaeeeeeeeeeeneeee 5 Design and Implementation e 6 4 HR cca 6 4 2 Device Drivers for the nRF24L01 licia 8 4 3 Lab Exercise 1 Receiving a Broadcast from
7. Enhanced Shockburst is enabled the number of packets per second received with a 1 byte payload size fell from 4900 to 2933 yet surprisingly with a 32 byte payload size the cost of using Enhanced Shockburst was insignificant with the packets per second falling from 2160 to 2150 18 5 3 Evaluation of the Lab Exercises The three lab exercises functioned as designed However testing could only be done with one base station and up to four transmitters simulating four players for the wireless game due to limited transceivers and manpower for setting them up The wireless game was playable when used with four transmitters that were located on two adjacent workbenches The scalability of the exercises to a lab section of 20 students could not be tested due to insufficient transceivers and manpower it is possible the large number of transmissions occurring simultaneously could interfere with each other Using different frequencies for each star network of 1 base station and up to 6 student setups might alleviate this problem Based on the results from evaluating the throughput of the transceiver using different payload sizes lab exercise 2 could actually be improved significantly Instead of sending 1 byte packets which contain the real time value of the audio waveform as is done currently the transmitters should accumulate 32 byte sequences of values which represent the audio waveform over 32 time steps which are then sent as 32 byte packets to
8. TREAM uart putchar uart getchar _FDEV_SETUP_RW int main void PAYLOAD LENGTH 10 set the payload length of each packet init _RF 1 enabl nhanced shockburst set_RF_channel 8 can be used to change the RF channel to reduce interference set _RX addr PIPE ADDRESS 0 0 set _RX addr PIPE ADDRESS 1 1 set _RX addr PIPE ADDRESS 2 2 set_RX addr PIPE ADDRESS 3 3 set _RX_addr PIPE ADDRESS 4 4 set _RX addr PIPE ADDRESS 5 5 enable pipe 0 enable pipe 1 enable pipe 2 enable pipe 3 enable pipe 4 enable pipe 5 unsigned char pipe received uart_init stdout stdin stderr amp uart_str char packet char malloc PAYLOAD LENGTH while 1 if RX FIFO status 1 pipe received read RX payload packet 26 fprintf stdout lt s gt packet 7 2 3 2b Transmitter that transmits 10 byte packets to base station with Enhanced Shockburst enabled define PIPE ADDRESS 2 0xb4b5b602 int main void char transmission result PAYLOAD LENGTH 10 set the payload length of each packet init RF 1 init transceiver enabl nhanced shockburst set mode TX MODE set _RX addr PIPE ADDRESS 0 0 set_TX addr PIPE ADDRESS 0 char packet char malloc PAYLOAD LENGTH while 1 sprintf packet abcdefghij unsigned char transmission result transmit packet packet
9. ata i PAYLOAD LENGTH strncpy packet data i PAYLOAD LENGTH for j 0 j lt PAYLOAD LENGTH j fprintf stdout c packet j transmission result transmit packet packet E 7 2 3 1b Corresponding receiver that receives four bytes at a time with enhanced shockburst disabled define PIPE ADDRESS 0 0xb4b5b600 FILE uart str FDEV SETUP STREAM uart putchar uart getchar FDE int main void PAYLOAD LENGTH 4 set the payload length of each packet unsigned char pipe received unsigned char j uart_init 25 stdout stdin stderr amp uart str fprintf stdout starting n init _RF 0 disable enhanced shockburst set _RX addr PIPE ADDRESS 0 0 char packet char malloc PAYLOAD LENGTH while 1 if RX_FIFO status 1 pipe received read RX payload packet for j 0 j lt PAYLOAD LENGTH j fprintf stdout sc packet j 7 2 3 2a Base station that receives 10 byte packets from up to 6 transmitters with Enhanced Shockburst enabled define PIPE ADDRESS 0 0xb4b5b600 define PIPE ADDRESS 1 0xb4b5b601 define PIPE ADDRESS 2 0xb4b5b602 define PIPE ADDRESS 3 0xb4b5b0603 define PIPE ADDRESS 4 0xb4b5b604 define PIPE ADDRESS 5 Oxb4b5b605 FILE uart str FDEV SETUP S
10. eded char packet char malloc PAYLOAD LENGTH packet 0 A transmission result transmit packet packet The program that is receiving packets should call RX_FIFO_status void to check whether packets have been received it returns 0 if no packets are in the RX FIFO and 1 if packets are present The transceiver automatically places packets in the RX FIFO when they are received Once packets have been received they can be read from the RX FIFO by calling read_RX_payload char buffer char pipe received pipe on which the packet was received while 1 if RX_FIFO status 1 pipe_received read RX payload packet fprintf stdout lt s gt packet 24 7 2 3 Examples 7 2 3 1a Transmitter that broadcasts a string four bytes at a time with enhanced shockburst disabled define PIPE ADDRESS 0 0xb4b5b600 char data The purpose of this course is to enable students to carry out sophisticated designs of the modern digital systems which now appear in products such as automobiles appliances and industrial tools n int main void unsigned char i unsigned char j char transmission result PAYLOAD LENGTH 4 set the payload length of each packet init _RF 0 init transceiver disable enhanced shockburst set_mode TX MODE set _RX_addr PIPE ADDRESS 0 0 set_TX addr PIPE ADDRESS 0 char packet char malloc PAYLOAD LENGTH while 1 for i 0 i lt strlen d
11. ich is set up by the instructor or teaching assistants Depending on the number of students and the number of clients that each base station can handle multiple base stations might have to be used The program running on the base station would have to be designed to be fault tolerant and resilient to errors in the data sent by the students so that errors by a group would not hamper the use of the base station by other groups The lab exercise has to be designed such that students can finish it in one or two afternoons in a lab setting Device drivers will have to be written and documented to provide a hardware abstraction layer for the students to interface with the transceivers The drivers will be written in C and used as part of the programs that students will implement and run on the Mega644 microcontrollers 3 Possible solutions and related work The usage of the ATmega644 and nRF24L01 for the hardware was specified as per the design requirements Another student at Cornell Jaehyun Kim 3 had previously written an API for the nRF24L01 that was capable of basic point to point communication between two transceivers However that API does not support features such as multiceiver receiving from multiple transceivers in a star network and using auto acknowledgements for reliable communication The API also has problems with switching between transmit and receive modes requiring the transceiver to be powered down when switching modes There
12. icrocontroller on a student setup reads the value of the 10KQ trimpot connected as shown above using the analog to digital converter on the ATmega644 and detects button presses on the STK500 SWO and SW1 on the STK500 are connected to Port CO and C1 respectively on the ATmega644 The program on the microcontroller encodes the information as a string with the student s NetID as the first 6 characters F or B for the 7th character to indicate forward or backwards acceleration and a value from 0 255 corresponding to the trimport reading for the last three characters If the NetID or trimport reading are shorter than 6 and 3 characters respectively they are padded with spaces to keep the string length consistent Examples of strings are yl478F 80 and abc123B150 The strings are transmitted by the student setups to the base station Similar to lab exercise 2 there is one base station configured in multiciever mode for every six student setups and each student transceiver uses a unique address The base station sends the received strings to the computer using the serial connection adding the lt and gt brackets around the string so that the Java program can detect the beginning and end of each string The game program is written in Java and runs on a computer connected to the base station This was done because of the ATmega644 does not have an integrated VGA module and manually generating an NTSC signal using software in the microco
13. is also a comprehensive set of drivers written by Brennan Ball of diyembedded com 4 but it is incompatible with the ATmega644 since they were written for the LPC2148 and PIC18F452 microcontrollers decided to write a new set of drivers based on the documentation by Brennan Ball and reusing some of the code by Jaehyun Kim such as the mappings from register names to addresses macros for commands and some of the functions for setting the TX and RX addresses One of the main challenges with using the nRF24L01 is the complexity involved in configuring and controlling it through multiple commands sent by SPI unlike simpler transceivers such as the Radiotronix W1 232 series which require minimal configuration Thus in order to make it easier for students to use the transceiver designed my drivers to be easy to use by automatically doing many of the steps involved in setting up and operating the transceiver This does come at the expense of configurability since some of the options are not exposed to the user through the API 4 Design and Implementation 4 1 Hardware The wireless transceiver to be used in the exercise is the Nordic Semiconductor nRF24L01 The transceiver operates in the worldwide ISM frequency band at 2 400 2 4835 GHz and support air data rates of 1 Mbps and 2 Mbps 2 The transceivers are controlled through a Serial Peripheral Interface SPI where operations are performed by writing and reading registers in the nRF24L01
14. nt T_T Student Student Base Station 5 Speakers Figure 5 Structure of lab exercise 2 The second exercise involves students transmitting audio signals to the base station which plays them using speakers that are connected to it The audio signals are sent in the form of sequences of values ranging from 0 to 255 which are converted to analog signals using pulse width modulation on the OCOA port of the ATmega644 The exercise was designed as an extension to the Audio Sequencer and Synthesizer lab exercise 6 with audio signal being generated using direct digital synthesis with the code from that lab exercise After students have constructed the synthesizer they can send their audio signal wirelessly to the base station which would combine all the signals received from various groups and play it resulting in interesting tunes based on combinations of student inputs 11 ti A eee WY iN Figure 6 Base station connected to speakers Each base station is configured as a multiciever capable of receiving from six transmitters with different addresses These addresses are defined as PIPE_ADDRESS_0 to 6 in the Wirelesslab4760 file Each student transceiver will be configured to use a unique address Auto acknowledgements are not used for this exercise in order to maximize throughput on the base station 12 4 5 Lab Exercise 3 Wireless Multiplayer Game
15. ntroller results in relatively low resolution black and white graphics The Java program reads the player commands from the serial connection using the jSSC java simple serial sonnector library by Sokolov Alexey 7 The program then performs the physics computations for the game and displays the state of the game on the screen The computations used to simulate the elastic collisions of particles are based on the Video Game Particle Beam lab from the 2011 offering of ECE 4760 by Bruce Land 8 15 The techniques learnt in this exercise can be applied to applications where microcontrollers are deployed to collect information such as sensors in the field and transmit back data wirelessly to a base station which uploads the data to a computer for logging Originally my plan for this exercise was to have two way communication between the base station and the student setups where the base station would reply with the coordinates of the players and cows and the students could write scripts or Al programs to automatically play the game or display the game on their own screens by sending the coordinates to their computer by a serial connection However it proved unfeasible to send the replies using the piggybacking payloads on ACKs feature since the TX FIFO could only contain up to three packets as described earlier Having the base station switch to TX mode to transmit is slow and it would miss packets that are sent to it by students while
16. o the nRF24L01 that supports auto acknowledgements and retransmission of packets to achieve reliable communication at the expense of reduce throughput A receiver in multiceiver mode can receive transmissions from up to six transmitters This is done by enabling up to six data pipes and setting the RX receive addresses for each pipe to correspond to the TX transmit address of each transmitter The Enhanced Shockburst link layer also supports advanced features such as dynamic payload length and piggybacking payloads on the auto acknowledgements sent from the receiver to the transmitter However to keep the drivers easy to use decided not to use these features and instead use static packet sizes that are set by the user at initialization The piggybacking payloads on ACKS initially seemed to be an attractive way of sending replies containing data from the base station to the student setups however there is a hardware limitation in the transceiver that limits the use of this feature A payload can be included in an ACK packet from the receiver to the transmitter The TX FIFO transmit first in first out which the payloads are stored in can only contain three pending payloads when ideally one would want capacity for six payloads one for each pipe Sharing the three slots among six pipes presents problems such as slots in the TX FIFO getting blocked if a transmitter stops communicating with the receiver while there is a payload pending f
17. of Cornell University In the course students are taught to use design real time digital systems using microprocessor based embedded controllers The course is taught by Bruce Land who is also the advisor for this project The goal of this project is to develop a lab exercise for ECE 4760 involving wireless communication between two microcontrollers The course would benefit from the addition of this lab exercise as it gives students experience with using wireless transceivers and teaches them how to add wireless communication capabilities to the electronic systems that they design Even within the course students can build on what they have learnt in this lab to explore interesting applications involving wireless communication in their final design project where students design and implement a microcontroller project of their choosing Given the rapid proliferation of wireless features in electronic devices such knowledge would be helpful in their future careers as electrical engineers The lab exercise will involve the use of 2 4 GHz transceivers for wireless communication Each transceiver will be connected to an Atmel Mega644 microcontroller on a STK500 development board or the prototype board designed by Bruce Land and Nathan Chun Based on the typical student enrollment in ECE 4760 each group of two students would have access to one STK500 Thus the exercise has to be designed such that several groups of students connect to a base station wh
18. operating the nRF24L01 Three lab exercises of increasing complexity that demonstrate the usage of the transceivers in different applications were developed The first exercise has students receive a message that is broadcast from the base station The second exercise has students transmit an audio signal to the base station which plays the audio using speakers that are connected to it The third exercise is a wireless multiplayer game involving elastic particle collisions where player control their character by sending commands to the base station The base station then passes the commands by serial interface to a Java program that runs the game and displays its graphics The range and performance of the nRF24L01 in the Philips Hall Digital Lab environment was analyzed by measuring packet drop rates without the use of the Enhanced Shockburst link layer for acknowledgements and retransmissions The range of the nRF24L01 in the lab environment was found to be limited due to the large amount of electronics and metal objects in the lab which obstruct the RF signals The throughput that can be achieved when the nRF24L01 is used with the ATmega644 was also measured lt was found a significant overhead is incurred in transmissions and thus using a large payload size up to 32 bytes for each packet resulted in maximum throughput 2 Design Requirements ECE 4760 is a senior level course offered by the Electrical and Computer Engineering Department
19. or the transmitter resulting in the payload staying in the FIFO indefinitely and preventing the use of the slot by other payloads The user would have to manually implement some mechanism to detect such occurrences and flush the TX FIFO in order to share the three slots among six pipes 4 3 Lab Exercise 1 Receiving a Broadcast from the Base Station de ui Student gt Student Station lie Student Figure 3 Structure of lab exercise 1 Base The first exercise involves receiving packets which are broadcast from a base station This exercise can be used by students to check that they have connected the transceiver correctly and the SPI communication to the transceiver is functioning Figure 4 Console output of the received broadcast All the transceivers are set to use the same address The base station is set to TX mode and continuously transmits characters from a string while the student transceivers are set to RX mode and listen for the transmissions from the base station printing the received characters to the console There only needs to be one base station for any number of receivers as long as the receivers are within range Auto acknowledgements are not used for this exercise since they are designed for transactions between one transmitter and one receiver whereas in this exercise we have multiple receivers 10 4 4 Lab Exercise 2 Sending an Audio Signal ee Stude
20. real time This modification would result in better efficiency and thus higher throughput it would also allow the use of Enhanced Shockburst to prevent audio distortions from dropped packets 8 Special Thanks would like to thank Bruce Land for his advice and guidance on this MEng project and Jaehyun Kim for his prior work on the nRF24L01 some of which this project is based on 20 7 Appendix Schematics t l The following schematic shows the connections between the nRF24L01 and the ATmega644 BI0Y BHd 909 Bd 2odv avd Edy ied pode ped S300 SHd 90dv Sid 2909 720d aL Bad L 8d ON lY 29d NEY Ead 55 8d SOW SAd 0S W 9Ad AIS 28d 139537 IBLX 2IHLX PEEL 330 a Mega644 32 NI OND 195 780d 9as Id XIL 29Id SWL C9d oaL rId aL SId ISOL 799d 29S0L729d axa 0d axle tdd BLNE 720d CLNE edd acao rOd 96 504 dE 790d 200720 21 7 2 User Manual for nRF24L01 Device Drivers 7 2 1 List of Files The device drivers consists of four files wireless h Header file for the driver functions that are called by the user as well as helper functions wireless c Driver functions that are called by the user as well as helper functions Some of the functions are based on code by Jaehyun Kim cmd_list h Macros for commands that sent to the nRF24L01 by SPI written by Jaehyun Kim These are only used internally be drivers the user doe
21. s not need to know them register_map h Mappings from register names to their addresses written by Jaehyun Kim These are only used internally be drivers the user does not need to know them 7 2 2 Description of Functions and Usage Initializing and configuring the nRF24L01 All the initialization can be done in the main method of the program The user first has to set the value of the payload length This must be done before calling any of the functions in wireless c PAYLOAD LENGTH 1 any number from 1 to 32 init_RF unsigned char enhanced_shockburst_enable is then called to configure and power up the receiver enhanced_shockburst_enable is set to 0 to disable Enhanced Shockburst and 1 to enable it The function also automatically 22 configures parameters such as the transmission power and data rate for the user in order to make the drivers easy to use init_RF 1 init transceiver enabl nhanced shockburst init_RF 0 init transceiver disable enhanced shockburst The transceiver is initially configured to be in RX mode to change modes the user has to call set_mode unsigned char mode where mode is either RX_MODE or TX_MODE By default data pipes 0 and 1 are enabled to enable additional pipes the user can call enable_pipe unsigned char pipenumber where pipenumber can be from 0 to 5 nable pipe 4 enable data pipe 4 The RX and TX addresses have to be set by calling set_TX_addr
22. switching and transmitting Two way communication might be more feasible in a lab exercise that did not involve real time game play such as a turn based game 5 Results In order to analyze the range of the nRF24L01 and its throughput when used with the ATmega644 one setup was set to transmit packets continuously while another ran a program that receives those packets and records how many packets it receives per second The files used are located in the Measure rate directory of the code submission An interrupt service routine ISR is used to measure time in the receiver Every 10 seconds the program takes the count of the packets it has received in the last 10 seconds and prints the packets received per second to the console 16 By disabling Enhanced Shockburst and measuring the number of packets received and hence the packet loss rate when the receiver is placed at various locations in the Philips Hall Digital Lab observations can be made about the range of the transceiver in the lab environment A distance of about a quarter of the lab approximately 4 meters was resulted in a packet loss rate of 5 to 10 At a distance of about half the lab approximately 8 meters a large packet loss rate of about 30 occurred When placed at opposite ends of the lab the receiver failed to receive most of the transmitted packets 17 The limited range of the transceiver was possibly due to the large amount of electronics and me
23. tal objects in the lab which obstruct the RF signals Placing the transceivers at a high altitude helped to reduce the packet loss rate 5 2 Throughput of the Transceiver when used with the ATmega644 The transmitter and receiver were placed half a meter from each other and the throughput was measured with various payload sizes and settings for Enhanced Shockburst With a payload size of 1 byte and Enhanced Shockburst disabled an average of 4900 packets were received per second When the payload was increased to 4 bytes 4580 packets were received per second With the maximum payload size of 32 bytes an average of 2160 packets were received per second The less than proportional decrease in the rate at which packets are transmitted or received as the payload size increases indicates that overhead comprises a significant part of the delay involved in sending each packet Based on the nRF24L01 documentation one of the main contributors to the overhead could be the TX settling delay of up to 130 us that the transceiver goes through whenever it switches from standby mode to TX mode the transceiver is not supposed to be kept in TX mode continuously it automatically switches to standby mode once the TX FIFO has been emptied Based on these results using a large payload size is more efficient and results in a higher throughput since more data is transmitted per packet while the rate at which packets is not decreased by the same extent When
24. the Base Station 9 4 4 Lab Exercise 2 Sending an Audio Signal 11 4 4 Lab Exercise 3 Wireless Multiplayer game 13 Reuss 16 5 1 Range of the Transceiver in the Philips Hall Digital Lab Environment 17 5 2 Throughput of the Transceiver when used with the ATmega644 18 5 3 Evaluation of the Lab EXxErcises i 19 CONCIUSIONS ciccia 20 lt F ture Work 20 Special Thaks issii a akra ale 20 SAPPENO eae nee ee eer ee eee eee eee ee er oe ee ee ee eee ee ee 21 Ss Science 21 9 2 User Manual for nRF24L01 Device Drivers i 22 92 15 LISFONMIOS suna ira lla 22 9 2 2 Description of Functions and Usage 22 9 2 3 EXAMPIOS scala 23 1 Executive Summary In this project a wireless lab exercise is developed for the ECE4760 Digital Systems Design using Microcontrollers course The lab exercise involves the use of Nordic systems nRF24L01 transceivers for wireless communication between Atmel ATmega644 microcontrollers The exercises are designed such that several groups of students connect to a base station which is set up by the instructor or teaching assistants Since each nRF24L01 can receive from up to 6 transmitters when set up in a star network each base station can support 6 groups of students Device drivers compatible with the ATmega644 were written for configuring and
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