Full report - ECE - Cornell University
Contents
1. PAQ ADCA PALZADCL PA27ADC2 PA3 ADC3 PA47ADC4 PAS ADCS PA6 ADC6 PA 7ADC PB T PB1 T1 PB27A ING PB3 AINL PB4 SS PBS MOS PB67M SO PB SCK RESET XTAL 1 XTAL2 AREF AYCC PC 7SCL PC1 SDA PC2 TCK PC3 TMS PC4 TDO PCS TDI PC6 TOSC1 PC TOSC2 PD RXD PD1 TXD PD27INT PD3 INT1 PD470C1B PDS 0CLA PD6 ICP PD770C2 vpIVIJWLL GND GND RESET NC OSCI asca n 4 ft w fu A fa 3 30UT Bruce Land Nathan Chun 57972010 A 4 Circuit Board Layout Fig 3 Top Copper Layer and Silk Screen et prezy oo0o0000000 O O oO je ooo 0 00 Fig 4 Bottom Copper Layer and Silk Screen 990000090900000000900000000000900000000 E aja Se oar om mo ooooooodod 0080000000 colt aM wf A EN m o 3 Mega644 Mega32 oB E IS o m s Omz am oo En O00000 00000000000000 wike Vee Yta QoL ieee en m 000 o muj m a fo a 160k O ire NathanChun Cornell ECE476a 22pt Z2pf gn Fig 5 Silk Screen Pads and Vias2. The initial prototype board as described above was connected to a computer and the interface was verified to work properly both in transmit and receive modes The microcontroller was programmed with the Interrupt Driven UART Test Program available on the ECE 4760 class website 7 running at the default baud rate of 9 600 This program was designed to receive a serial input from HyperTerm and transmit the appropriate response to the user at the terminal The design passed the test successfully and proceeded to the next phase of testing As discussed in the previous section 5 1 speed tests were performed to measure the speed of the interface The final phase of testing involved several iterations of the printed circuit board to test the user interface aspect of the system and find out if there were any barriers to properly and easily utilizing the design As discussed above in section 4 3 ease of setup and use determined certain design changes that resulted in the final version submitted in this paper 6 Acknowledgements The author would like to thank Bruce Land Senior Lecturer Cornell University for his assistance and Scott Coldren Manager of Student Services Cornell University for his support A Appendices A 1 Online Resources and References 1 ADC UART Interface Test Program http courses cit cornell edu ee476 labs s2010 lab4code ADCtest zip 2 ArduinoBoardMega http arduino cc en Main ArduinoBoardM
3. 4760 in mind The current situation does not allow students to easily work outside of class due to restrictions on access to the relatively expensive equipment This device addresses this concern by providing students with an inexpensive method of working on projects outside of class This device provides students with the flexibility to explore the projects and the material in a greater depth It makes executing projects easier and simpler by minimizing unnecessary overhead in terms of complexity and difficulty as well as lower costs for the class to be run as the equipment required will be simpler cheaper and more accessible Throughout the several iterations of the design from circuit diagram to printed circuit board certain tests and verification were performed in order to gauge the performance of the product Functional tests allowed the design to proceed past the initial prototyping stages Speed tests showed that using MATLAB a bit rate of 9 600 baud can be achieved and speeds using HyperTerm can reach 57 600 baud Operational tests revealed weaknesses the intermediary prototypes that were barriers to one of the critical aspects of the design ease of use The final design provided a functional and flexible rapid prototyping platform based on the Atmel ATmega644 microcontroller specifically designed for use by the students of ECE 4760 2 Design Problem 2 1 Overview ECE 4760 at Cornell University is a microcontrollers class tau
4. screen as the system attempted to parse the data The first prototype required that the transmit and receive jumper pins be disconnected and reconnected at specific points in the connection process an action judged to be unnecessarily complicated The final revision addressed this concern by isolating the power to the interface chip from the power to the microcontroller allowing each to be independently activated This design utilizes the regulated 5V supply on the USB bus line to power to the interface chip allowing the serial connection to be created by the interface program on the PC while the microcontroller is unpowered and quiet 5 Results 5 1 Comparison to Original Expectations According to the manufacturer the FT232RL interface chip is capable of operating at 3 000 000 baud 6 During speed testing using the ADC UART Interface Test Program 1 the data rates achieved were significantly lower HyperTerm was stable up to 57 600 baud and no higher while MATLAB was operational at or below the default 9 600 baud rate Possible reasons for these shortcomings may be the fact that the overhead involved in reading the serial input take too much time and allow the terminals input buffer to be overwritten as it is being read resulting in invalid data acquisition 52 Verification In order to verify that the design is robust and works as expected the system was put through rigorous functionality quality and operational testing
5. B must be opened prior to connecting the USB cable due to the fact that MATLAB requires that it be the first to connect to the port If you receive an error when attempting to open the connection unplug the USB cable restart MATLAB plug in the USB cable and then attempt to open the serial port Create serial object at COM Replace with the appropriate port number SO serial COM OPTIONAL Set the input buffer size to 32 bytes to only read the more recent entries to compensate for MATLAB s overhead set SO InputBufferSize 32 oo o Open the serial object fopen SO oo Read data from serial port Ss can be replaced with any standard c formatting string s reads an array of characters and can be parsed by index x hex2dec readin 4 6 readin fscanf SO s do do oo oo here is an example code snippet that continuously plots the last hundred data points initialize arrays x 1 100 y zeros 1 100 set up plot hold on p plot x y ylim 0 255 oo oo while 1 read input readin fscanf SO 3s extract necessary data and concatenate to data arrays y horzcat hex2dec readin 11 12 y 1 99 x xt 1 update plot and redraw set p xdata x set p ydata y xlim x 1 x 100 drawnow end Close the serial object fclose SO Delete and clear the serial object variable delete SO clear SO A 3 Circuit Schematic
6. NEXT GENERATION ATMEL ATMEGA644 PROTOTYPE BOARD A Design Project Report Presented to the Engineering Division of the Graduate School of Cornell University in Partial Fulfillment of the Requirements for the Degree of Master of Engineering Electrical by Nathan Isaac Chun Project Advisor Bruce Land Degree Date May 2010 Abstract Master of Electrical Engineering Program Cornell University Design Project Report Project Title Next Generation Atmel Mega644 Prototype Board Author Nathan Isaac Chun Abstract The next generation prototype ATmega644 board allows students in ECE 4760 Digital Systems Design Using Microcontrollers to execute labs with a minimum of overhead and unnecessary complexity in set up The legacy system involves using a large development kit that requires obselete connections and converters to connect to the computer The proposed prototyping board has a microcontroller to USB to PC interface to create a small cheap portable system that very simply can be used with a solder less breadboard for labs and projects The next generation prototype board involves PCB design and production and interface construction and testing in order to create a small board that can be mass produced for future classes Report approved by Bruce Land Date 1 Executive Summary The next generation Atmel ATmega644 prototype board described in this paper has been designed with the Microcontrollers class at Cornell University ECE
7. ce would likely consume a good deal of memory and speed in the microcontroller a very large drawback to any solution 4 Documentation 4 1 Design The circuit design is heavily based on the interface used by the ArduinoBoardMega 2 a system popularly used by hobbyists and designed around the ATmegal280 a larger version of the ATmega644 used in this project 3 There were a few changes from the original Arduino design The reset hardware control line RTS was disconnected since this design didn t need to incorporate the reset functionality The LED status lights were removed from the design to keep the layout small and compact The ferrite bead on the VCC line was ignored as the device did not need the extra noise protection as it will primarily be used in environments where interference is minimal As discussed in more detail in section 4 3 the final design uses two power supplies the bus power for the interface chip and a separate power supply for the microcontroller differing from the Arduino design where both the chip and the microcontroller are on the same power line Ba B7 Vee AG E j eo ca Ga D Da SBVCE and luf Vee Li Lu C FTDL FT23eR E em my Mega644 Mega32 mj rl TX ei oN A ma QT sete eg CMA 9 1l2u a ei 26 JMP 300 j LAAk luf E mjn m E UL L 2011 BruceLand NathanChun Cornell ECE476a 22PE 22pE gnd Fig 1 Final Printed Circuit Board Design The layout of the board is based on the cu
8. ega 3 Atmel ATmega644 Datasheet http www atmel com dyn resources prod documents doc2593 pdf 4 Atmel STK500 Product Page http www atmel com dyn products tools card asp tool id 2735 5 ExpressPCB http www expresspcb com 6 FD TI FT232RL Datasheet http www ftdichip com Documents DataSheets DS FT232R pdf 7 Interrupt Driven UART Test Program http courses cit cornell edu ee476 labs s2009 lab3code SeriallSRversion zip 8 MATLAB Serial Port Information Page http www mathworks com access helpdesk help techdoc matlab external f38496 html 9 Prototype Board for Atmel Mega644 http www nbb cornell edu neurobio land PROJECTS Protoboard476 index html 10 SparkFun Electronics Breakout Board for FT232RL USB to Serial http www sparkfun com commerce product info php products id 718 11 V USB A Firmware Only USB Driver for Atmel AVR Microcontrollers http www obdev at products vusb index html A 2 User Manual A 2 1 USB Connection Guide Sample code available on the ECE 4760 website demonstrates how to program the chip to enable UART To change the baud rate of the microcontroller change the define UART_BAUD value in uart c The following list of steps demonstrates how to properly connect the protoboard to a Windows computer e Turn off the power to the microcontroller using the switch near the power socket of the protoboard e Use the USB cab
9. ght at Cornell University using the Atmel ATmega series of chips The typical development environment utilizes the Atmel STK500 a starter kit and development system for Atmel s AVR Flash microcontrollers 4 While this is a fully featured development suite designed for use with Atmel s entire line of microcontrollers it is also expensive requiring that the development kits be used only in lab under TA supervision The class work is almost completely based on projects and lab time is crucial to the execution of the projects Since the lab is only open for limited times due to need of TA supervision access to the equipment needed to complete the assignments is limited making it unnecessarily difficult for students to work on the projects This paper addresses this concern by outlining the design for a small inexpensive rapid prototyping board that can be used to replace the larger and more restrictive current setup 2 2 System Requirements and Design Specifications The board and interface design proposed must e Be intuitive to use e Operate in a stable manner e Be inexpensive e Use off the shelf components e Be able to be assembled by hand e Allow for flexibility for use in rapid prototyping projects 3 Solution 3 1 Potential Solutions Currently there is a prototype board designed by Bruce Land that solves some of the issues posed in the previous section but its effectiveness is limited by its reliance upon anti
10. le to connect the protoboard to the computer e Open the Windows Start menu right click on My Computer select Properties to open up the System Properties dialog o Alternatively select System in the control panel e Under the Hardware tab click Device Manager e In the Ports COM amp LPT category in the device manager list look for the USB Serial Port COM entry will be replaced with a number that indicates the port to which the interface is assigned o To change the baud rate the chip is operating at right click on the USB Serial Port COM entry and select Properties Under the Port Settings tab change the Bits per second setting to the desired baud rate e Open the connection using a serial interface program e g HyperTerminal using the selected baud rate 8 data bits None parity 1 stop bit and None flow control 8 N 1 e Once the connection has been opened turn the Microcontroller on e DO NOT disconnect the USB cable or else you will have to repeat the steps to connect over again NOTE It is possible to bus power the microcontroller by running a wire from the USBVCC header pin to the VCC header pin During connection with the computer this wire must be disconnected to cut power to the microcontroller A 2 2 MATLAB Connection Guide 8 The following code can be used to connect MATLAB to the serial interface NOTE MATLA
11. quated technology This smaller prototype board uses an RS 232 DE 9 serial interface to communicate with the PC As most laptops do no longer have a DE 9 port more equipment is required to convert the serial data to USB which is a more popular standard The design proposed in this paper is heavily based on this design using a USB interface instead of the older RS 232 Several chips are commercially available to convert an RS 232 signal to USB FTDI produces the FT232 and the FT245 Prolific produces the PL2303 and the PL2313 Silicon Laboratories produces the CP2102 and CP2103 Another possible solution to the interface problem uses onboard USB where the microcontroller itself reads and writes directly to the data stream V USB is an example of a piece of code that can be programmed into the chip to interface with a USB port 11 3 2 Selected Solution The chip selected for use in the final design was the FT232RL a USB to serial UART interface chip in a SSOP 28 package This solution was chosen for the following reasons e It has been widely and successfully used in a variety of applications e Its operation is well documented 2 6 10 e There are many example circuits to use as references e It comes in a manageable package large enough for hand soldering An onboard USB solution was not selected because of the excess complexity that the user may have to deal with as well as the fact that the complicated and multilayered interfa
12. rrent generation of ATmega644 prototyping boards designed by Bruce Land 9 It contains a power socket and voltage regulator to provide a regulated 5V power supply to the microcontroller a 16 MHz crystal oscillator a test LED to demonstrate proper functionality a 6 pin ISP programming header the USB interface chip and a USB B socket 4 2 Implementation The first circuit was built on a solder less protoboard for initial functionality testing and to decide whether or not to pursue the proposed design Since the design worked properly the next step was to create a printed circuit board layout The final product was designed in ExpressPCB s layout software and fabricated by ExpressPCB The printed circuit board was then populated by hand with header pins in each of the 36 pins lining the top of the board to allow the protoboard to be plugged into a solder less breadboard for easy use ei 4 3 Major Design Changes Since this product is supposed to be designed for ease of setup and use accessibility was a critical factor in its production The initial layout failed this requirement as opening a serial connection to the board was complicated and convoluted While the connection is being opened the microcontroller transmit and receive pins must be in a quiescent state to avoid the computer interpreting signals improperly in one case the USB serial interface to an ADC was treated as a mouse causing the cursor to jump wildly across the
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