PolyBot Board: a Controller Board for Robotics Applications and
Contents
1. and Figure 2 the board is shown with the jumpers installed For the analog and digital inputs we use connectors similar to the HandyBoard 7 The connectors are 3 pin connectors with a 5V ground and an input pin This type of connector works well because it allows sensors to be moved among the different input pins without hav ing to re wire the sensor leads There is also an 8 pin digital I O header which provides access to 5V ground and 6 digital I O pins A 4 pin header allows access to the SPI port For the download cable connection we use an RJ 45 connector This type of connector was chosen because of the positive locking it provides with repeated connects and disconnects 6 Downloading to the PolyBot board Program download is performed over the parallel port through a download board A picture of the download board is shown in Figure 4 The board provides an in terface between the parallel port and the SPI port of the ATMega32 which is used in programming the chip A 10 pin IDC connector is located on the right end of the board as shown in the figure and is used to connect the board to a computer parallel port A standard Cat 5 Eth ernet cable is used to connect the download board to the PolyBot board The download board contains a CMOS buffer 74HCT541 which is used to maintain signal lev els from the parallel port to the controller board Two LEDs indicators are provided on the download board to indicate connec2. i i L IM OOE Figure 2 PolyBot board without LCD display A Basic Stamp 9 module provides excellent soft ware support and programming interface but is not in tegrated into a robot controller board providing support for direct actuator interfacing such as DC motors 3 PolyBot Board The PolyBot board is a controller board developed at Cal Poly for robotics education and applications The PolyBot board has the following features e physical size is 3 x4 e 16MHz ATMega3 2 microcontroller e 8 digital inputs e 10 analog inputs e 8 hobby servo outputs e 4DC motor outputs e software controlled LED e 16x2 LCD display with backlight e 200mA relay solenoid port As previously discussed the design for the board was inspired by a number of different robot controller boards but all of the available boards considered had positive aspects and negative aspects We decided that no one available board would meet our needs as a robot controller board As aresult we designed the board con sidering the most common and required features for a small mobile robot design Figure 1 shows the board with the LCD display mounted and Figure 2 shows the board without the display In addition to the previously listed functionality we chose to design a board around the following desired cri teria e All ICs must be in a DIP package e All ICs must be socketed e Built in support to run board logic servos and DC mo
3. we selected a standard 2 5mm inner diameter jack 5 5mm outer diameter This power jack allowed the design to eliminate a power switch from the board A user can quickly remove power by pulling the plug from the jack JP_PWR is a 3 pin male header which allows a user to enable the on board 5 volt regulator If the regulator is enabled via a short ing jumper the board may be powered with 7V 20V If a user disables the regulator then the board must be powered with exactly 5 volts The PolyBot board provides support for connecting up to 8 hobby servos Hobby servos typically come with a 3 pin 5V power ground and signal input fe male header with 1 spacing This standard spacing was used on the PolyBot board For each of the RC servo connectors on the board we use a 3 pin male 1 spac ing connector This provides a very positive and durable connector for the servos For the DC motors we use 3 81mm spacing screw terminal type connectors These were selected because of the higher current that they can carry and because they allow for different sizes of wire to be used for the motors For the DC motor and servo external power in puts we also use the same 3 81mm spacing screw termi nal connectors There are standard 1 spacing shorting jumpers used to connect disconnect the external motor and servo power from the power applied to the power jack Two jumpers are used for each connection to han dle higher currents In Figure 1
4. PolyBot Board a Controller Board for Robotics Applications and Education John S Seng Dept of Computer Science California Polytechnic State University San Luis Obispo CA 93407 jseng csc calpoly edu Abstract In this paper we discuss the design and engineering of the PolyBot board a custom robot controller board This board has many features which make it suitable for use in the design and construction of a simple mobile robot We outline the design decisions made such as mi crocontroller selection input and output features board layout connector selection and software We discuss our experiences in using the board in an undergradu ate robotics class at Cal Poly State University San Luis Obispo 1 Introduction Robotics is a multi disciplinary field of growing im portance When integrated into an undergraduate en gineering curriculum a robotics course can provide an invaluable learning experience Students studying robotics are not only exposed to strictly software or hardware problems but also the challenges that arise from interactions between software and hardware At California Polytechnic State University San Luis Obispo the computer engineering department offers a course in autonomous mobile robotics This course is taken by computer science computer engineering and electrical engineering students One goal for the course was to teach students the robot building process by incorporating both an electrical e
5. ces flexibility in the design but allows isolation of noise between the logic and motors Finally because the boards would be used in a stu dent environment it was designed such that the power input was tolerant of a number of mistakes that could be made in powering the board Firstly the board should have a fuse to prevent damage should a short occur A motor may be stalled or a sensor may be wired incor rectly and these events should trip the fuse Secondly the board needed to be able to withstand a reverse po larity power connection If someone inadvertently con nects power and ground backwards to the board the board should be able to tolerate such a mistake To achieve our goals of input power protection we use a PPTC resettable fuse 1 85A coupled with a 1N5401 diode The diode does not conduct when the power is applied correctly this provide normal protection against over current situations When power is applied incor rectly the diode conducts through the fuse which trips the fuse and stops the flow of current Other features present on the board include a jumper to allow enabling disabling of the LCD display back light JP_BL in Figure 3 a software readable push button SW1 a software readable potentiometer a 2 pin header which can control a relay supplies up to 200mA and a software controllable LED 4 Microcontroller Selection Several microcontrollers were considered for the PolyBot board The Atmel ATMe
6. ction using the AVRCam 8 and shaft encoder implementation In addition to using the board in the mobile robotics class we also sell the unassembled kits to students As a service to the students the kits are sold at the cost of the parts and provide them with a source of low cost development boards for outside projects 9 Future Work The current version of the board uses a parallel port for downloading and the standard parallel port is be ing phased out as more and more computers switch to providing only USB ports We provide to the students a bootloader that can be used along with another cir cuit to download a program to a board using a standard RS 232 serial port or a USB to serial cable We have found that this solution works well for those students with computers without a parallel port We are working on a USB to RJ45 download board which will be back ward compatible with existing PolyBot boards In addition we are considering adding another micro controller to handle the servo and motor control These functions require a significant amount of CPU time from the microcontroller and can be off loaded to a smaller secondary microcontroller The current PolyBot board has met our goals for functionality For a next generation PolyBot board we intend to include the following features e Dual I C ports e Dual UART ports e Higher performance microcontroller e Larger flash memory and SRAM The architecture we will use
7. e by students providing good func tionality and having a low cost The PolyBot board has an Atmel ATMega32 micro controller a number of analog and digital inputs several hobby servo and DC motor outputs and an LCD display The total cost for printed circuit board manufacturing and parts has been very reasonable for use in a university environment By developing the board and purchasing the parts in quantity we were able to significantly reduce costs We have used the PolyBot board in an undergradu ate robotics course at Cal Poly State University This board has been successful in providing students with a platform to build small mobile robots References 1 AVRGCC GCC port to the AVR architecture Online Available http winavr sourceforge net 2 Philips LPC2138 Single chip 16 32 microcontroller Online Available http www semiconductors philips com pip LPC2132FBD64 html 3 Atmel Inc Atmel ATMega32 8 bit AVR Microcon troller with 32KB In System Programmable Flash On line Available http www atmel com products avr 4 B Dean AVRDUDE AVR down loader uploader Online Available http savannah nongnu org projects avrdude 5 S Imberman Teaching neural networks using lego handy board robots in an artificial intelligence course In Proceedings of the 34th SIGCSE technical symposium on Computer science education May 2003 6 D Kumar and L Meeden A robot laboratory for teach ing arti
8. e con nectors used on the PolyBot board Section 6 describes how software is downloaded to the board Section 7 outlines the documentation and software support for the PolyBot board Section 8 covers our experience with using the PolyBot board during a recent robotics course Section 9 describes future work Section 10 concludes 2 Related Work The PolyBot board is similar to a number of robot controller boards on the market today Small robot con troller boards typically include support for a number of analog and digital sensors some interface circuitry for DC motor control and some sort of user output whether it be an LCD display or simply a few LEDs Some ex ample small robot controller boards include the Handy Board the OOPIC R board and Basic stamp microcon troller modules The PolyBot board combines and enhances many of the ideas present in the Handy Board 7 The Handy Board has proven to be very successful for use in robotics classes 6 5 Some differences between the PolyBot board and the Handy Board include the use of a faster microcontroller the addition of external servo and motor power ports extra analog inputs configurable power input and power polarity protection The OOPIC R 10 robot controller board provides a more direct interface to the digital I O pins and provides more servo output ports It is a smaller board without support for direct physical attachment of an LCD dis play I l p l i
9. ficial intelligence In Proceedings of the 29th SIGCSE technical symposium on Computer science ed ucation May 1998 7 F Martin The Handy Board Technical Reference On line Available http www handyboard com 8 J Orlando The AVRCam Online Available http www jrobot net Projects AVRcam html 9 Parallax Inc Basic Stamps Online Available http www parallax com 10 Savage Innovations OOPIC The Object Oriented PIC Online Available http www oopic com 11 J Seng PolyBot board user s manual Online Available http www csc calpoly edu jseng PolyBot_Board html
10. ga32 3 was selected for a number of reasons The first reason is because of its high performance Although the microcontroller clock rate is 16MHz the CPU core is RISC based and delivers performance close to 1 MIPS per MHz Secondly the fastest version of this microcontroller is available in a DIP package Again the importance of the chip package cannot be overlooked because this is a board that will be used by students in various environments with various sensors and replacing a damaged microcontroller should be an easy task Thirdly the software tools available for the microcontroller are open source and run on multi ple platforms The compiler is based on GCC and the toolchain is based on GNU tools The compiler available is called AVR GCC 1 and runs on Windows Linux and Mac 5 Connectors Connector selection is an area that deserves care ful consideration when designing equipment for student use Firstly connectors need to be durable and reliable especially after repeated connects and disconnects that students perform when testing their robots Secondly the connectors also need to provide flexibility in the overall design Robot designs should not be particularly limited or restricted because of the number or type of available connectors This section describes why par ticular connectors were selected on the PolyBot board Figure 3 is a diagram showing all of the connectors on the PolyBot board For the main power input
11. ngineering and com puter science experience In the process of construct ing a robot the students gained an important experience in learning and understanding the interactions between robot hardware and software The lab component for this class was crucial Since one of the goals of the course was to teach engineering students how to build simple autonomous mobile robots the approach was to have students build their robots from the ground up A primary goal was to have the students fully understand the hardware of the robot controller board they were given We wanted to find a board that was easy to use had good functionality was relatively inexpensive and had free open source software tools To meet these require ments we decided to implement our own custom robot controller board the PolyBot board This paper outlines the design decisions made when engineering the PolyBot board We cover the process of selecting a microcontroller designing the board to protect against damage during use and features that are often required when designing small mobile robots In addition this paper covers our experiences in using the PolyBot board for a recent undergraduate robotics course This paper is organized as follows Section 2 cov ers related prior work Section 3 covers design de cisions made during the development of the PolyBot board Section 4 discusses selecting a microcontroller for a robot controller board Section 5 describes th
12. s on the PolyBot board 7 Documentation and Software We have written a user s manual 11 for the Poly Bot board Because the PolyBot board comes as an unassembled kit the user s manual not only includes in formation regarding usage of the board but it includes board assembly instructions For software support we have written a software li brary for the PolyBot board This library includes func tion calls to read the analog and digital inputs control the servo outputs control the motor outputs and display information to the LCD display We have found that pro viding a library greatly improves quality of the students robots In addition to the library students can modify all of the microcontroller pins and configuration registers directly from their C code 8 Course Experience We use the PolyBot board in an undergraduate mobile robotics course This course is intended to introduce stu dents to concepts in the design and construction of au tonomous mobile robots The course enrollment com prises of students majoring in computer science com puter engineering and electrical engineering For the class each pair of students receives the Poly Bot board as an unassembled kit The kit comes with a PolyBot board printed circuit board a download printed circuit board and all the necessary components to pop ulate the circuit boards The first laboratory for the class is to assemble the PolyBot board Even though st
13. tivity and data transmission status As an alternative to downloading through the parallel port we developed a bootloader that allows download ing through an RS 232 serial port This was possible be cause the RX and TX serial lines of the microcontroller are also routed to the RJ 45 jack When this bootloader is installed holding a pushbutton switch and pressing reset enables the serial download mode With the avail ability of USB to serial converters we found that this was a very useful option for those users who do not have access to a computer with a parallel port For the software to perform the downloading we use the open source download program AVRDude AVR Downloader Uploader 4 This program allows repro gramming of the fuse configurations bits and the pro gram flash memory JP_BL shorting this enables LCD backlight 4 pin SPI port can be used as digital I O ni 10 Analog inputs E 16 pin LCD connector a Reset of JP_PWR 3 pin logic power jumper short top 2 pins for regulated 5V short bottom 2 pins for direct power to logic 200 mA Solenoid relay output T 8 Digital inputs Sear GND 5V ee DC Power Jack center positive Jumpers for Servo Power jumpers run horizontally 1 0 External l Servo Ground External 4DC motor Jumpers for RJ 45 Power Motor outputs Motor Power Download Power jumpers run Connector horizontally Figure 3 Connector
14. tors at different voltages e reverse polarity and over current protection All integrated circuits needed to be available in a DIP package because it was planned that the students would assemble the controller board as a lab assignment in the class Although the trend in integrated circuit packag ing is toward smaller and smaller packages a DIP pack age makes sense for a student controller board Students with little or no soldering experience can assemble a board with chips with DIP packaging Another important consideration when developing controller boards for student use is having socketed in tegrated circuits which isolate the sensor inputs from the microcontroller Having this isolation prevents incor rect sensor wiring from directly damaging the microcon troller This situation is not excessively important when a microcontroller is as low cost as the ATMega32 but in cases where the microcontroller is more expensive this needs to be considered In our design we are able to iso late all the digital inputs and most of the analog inputs from direct connection to the microcontroller pins We were able to use chips in a DIP package for the analog and digital inputs Robot designs often use motors that require a voltage level different from the voltage for the logic Because of this it was important to have a board that supported sup plying the logic at one voltage and running the motors at a different voltage This not only enhan
15. udents taking the class entering with a wide range of experience levels in solder ing all of the students have been able to successfully as semble their PolyBot board kits Students with prior sol dering experience can readily assemble the board When having students assemble the boards it is important to perform a pre check process before they continue Have the students first solder on the chips but only 2 pins that are diagonally opposite After they have attached all IC sockets in this manner check to make sure the sockets are correct If all sockets are correctly then allow them to proceed Performing a pre check in this fashion allows easy removal of sockets if they were installed correctly We have had very high success rates with student board assembly For the robot chassis we use the ScooterBot platform from Budget Robotics www budgetrobotics com This chassis consists of 2 circular pieces of expanded PVC connected with tall aluminum standoffs This chassis Figure 4 The download board used to program the PolyBot board provided a well constructed platform which was pow ered using hobby servos The hobby servos were already modified to provided 360 degree rotation The hobby servos provided more than enough torque and speed for the applications the students were targeting Some of the lab assignments in the class included the following analog and digital sensor interfacing PID line following vision based color dete
16. will be the ARM7TDMI There are many microcontrollers based on this CPU core These include microcontrollers from Analog De vices SGS Thompson Atmel and Philips We intend to use the LPC2138 from Philips 2 The reason for se lecting the LPC2138 is that it comes with a bootloader in hardware that allows downloading over a UART serial port Since this is a surface mount chip with tight pitch the microcontroller will be already soldered to the board before distributing the kits to the students In order to prevent damage to the microcontroller we intend to use other socketed chips as interface chips If the damage occurs to one of these interface chips then it can be eas ily replaced with no damage to the LPC2138 The current board does not allow for RAM storage and this is something we would much like to see in a next generation board The LPC2138 provides 32KB of static RAM and 512KB of program flash memory These increases in memory size over the ATMega32 will allow more advanced work such as operating system develop ment on this platform Other future work we intend to pursue is to develop audio and DSP daughter cards for the PolyBot board This will allow us to use the board in classes other than the introductory robotics course 10 Conclusion The PolyBot board is a controller board that was de signed at Cal Poly State University for robotics educa tion The board was designed with the goals of being easy to use buildabl
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