CSC 578C Project 1 -- Semi autonomous platform
Contents
1. There are three main hardware components a PC and two Arduino stations 2 1 PC The PC component is used for debugging and interfacing with input devices A python program reads commands from a USB gamepad connected to the PC The commands are passed to the base station via UART serial connection Debugging on the PC uses a terminal to echo messages received from the base station Another program is used to live tune the remote station PID variables with the keyboard 2 2 Base Station Three components make up the entire base station The Arduino UNO board acts as a communication bridge between the PC and remote station Incoming instructions from the PC arrive through a serial UART connection and are marshaled into 32 byte packets which are relayed to the remote station over the wireless radio Debugging information received at the base station from the remote station from the wireless radio is echoed to the PC via serial UART Base Station Arduino Uno 2 2 Remote Station The remote station is where the meat of the project lies Most of the development time is spent on the remote station as it contains the actual motors and all the sensors A dismantled hard drive is used to provide a very smooth freely rotating disk A square styrofoam base is mounted on top of the exposed disk and secured with cable ties The following components are placed on top of the styrofoam base e two fans with motors two sonar sensors wireless2. thingm com products blinkm html About libraries Helps understand how compilers use the libraries http arduino cc en Hacking LibraryTutorial The datasheet above has detailed instructions on how to script the BlinkMs This means a list of instructions can be sent which will be executed in sequence by the LED See the Appendix for example code Here is a command shown in the datasheet n Oxff 0xff 0xff set full on bright white now The example code at thingm com uses a file called BlinkM funcs h which is a library that uses the functions in Wire h Note that BlinkM_funcs h contains code which should be moved to a cpp file before used in a project of any significant size Here is a snippet that plays a hardcoded script include WProgram h include Wire h tinc lude default address define blinkm addr 0x00 blin 1 1 1 1 1 tr Tie h c te Exe BlinkM funcs h km script line scripti lines E 255 00 00T 0x21 0x22 0x23 7 0x00 0x00 0x00 0x61 0x62 0x63 Oxfd Oxfd 0x01 0x02 0xfe 0xfe int scriptl len 6 main ini BlinkM playScrip for t0 BlinkM beginWithPower BlinkM stopScript blinkm addr BlinkM writeScript blinkm addr 0 scriptl len 0 scriptl lin Pa urn 0 number of dim whi dim whi dim whi mostly mostly script
3. te te te orange teal lines above es t blinkm addr turn off startup script 0 0 0 We also experimented with two BlinkMs for which we had to set their addresses The BlinkM func h library provides for this as well Sets the Uses g static void address Vire sen Vire sen Vire sen Vire sen Vire sen ure delay 50 I2C address of the eneral call broadcas Vire beginTransmission 0x00 DO a a d 0xD0 d bg TEI 0x0D dood d newaddress endTransmission just in case BlinkM t address BlinkM setAddress byte newaddress general call broadcast Since all the I2C devices are connected to the same bus we have disconnect all the other 12C devices when setting an address to a specific I2C device We also thought of using two BlinkM to obtain 16 different color combinations where each of the BlinkM would be assigned one of the four colors white red green blue easily distinguishable Our modified BlinkM library for this included the following functions detailed in the Appendix set up 12 void BlinkM begin for setting the address of each device void BlinkM setAddress byte addr used in SetoneBlink and twoBlinks void BlinkM SetColor byte red byte green byte blue set BlinkM at addr to color void
4. buttons is represented by a byte which greater than zero if the button is pressed and zero otherwise The directional pad is represented as two bytes one byte for up down and one for left right Each of these bytes has three status values up right 1 down left 1 neutral 0 Pressing up and right would result in two bytes both set to 1 The analog sticks are represented by two bytes each One byte for up down one for right left similar to the directional pad Each byte ranges from 100 to 100 depending on how far the stick is pressed in any given direction This results in a total of 12 2 4 18 bytes of data when reading the user input The number of bytes used can be reduced significantly by using a bit vector to represent the buttons and directional pad Reducing the bytes down to 6 bytes is a trivial exercise Despite the ability to reduce the bytes down to 6 this change was implemented and then removed The reason this feature required changes in the base station and remote station with little actual benefit in this current phase The radio sends packets larger than 18 bytes anyway and therefore the only communication that is reduced is on the serial port Since the data updates from the gamepad have a short delay leaving the original design has negligable performance degredation After reading input from the gamepad the program forwards the input to the base station over the serial UART connection We encountered an error where the
5. found in www maxbotix com uploads MaxSonar EZ1 Datasheet pdf We also tested it in pulse width mode but not before starting on the SUSs The SUS is a slick looking red US sensor with only three pins and only about 250 words we counted them in under two pages of well illustrated documentation Having been oversimplified to appeal to a wider audience the single signal pin of the SUSs proved to be an obstacle when wanted to use the same ATmega pin to time the pulse width outputs from two sonars see Section Hardware Interrupts Timers The problem of course is that it becomes impossible to trigger each sonar independently To solve this we first tried diodes in the following configuration We ran into troubles with diodes The most interesting one was that some of them allowed a 2uS back pulse that would sometimes trigger the other sonar Here is the logic analyser output showing that Channel 5 and 6 are the trigger outputs from the micro controller and Channel 7 is the input pin ICP1 We can see that Channel 6 was given a deliberate 10uS pulse from the Seeedstudio specifications and then we can see that return pulse from the sonar Channel 7 shows the same thing because of the orientation of the diode but Channel 5 should show nothing Instead it shows tiny 2uS pulses at each rising edge from Channel 6 Sometimes this fires the sonar sometimes it does not 5 Channels f Se Hu He 6 Channel 6 sensed 7 Channel 7 o We used an
6. means your compiler is not finding the appropriate libraries Make sure that you have I path to library for each of these in the makefile 5 4 Collaboration Tools Our team relied on Apache Subversion svn for version control and source code sharing For the uninitiated source code and other resources under version control is kept in an online database called a repository We request what is called a working version of whichever portion of the repository we would like We may make changes and upload them or update our working versions from the repository Local software called an svn client tells us the state of repository with respect to our working version When looking for a good svn tutorial google is your friend For Mac OS X a very good svn client is called Versions free trial Finally we used assembla com to host our repository
7. BlinkM SetoneBlink byte addr int color void BlinkM SetColor twoBlinks byte addrl byte addr2 int colorl int CoLorZ 7 a quick script on the microcontroller using SetonBlink void BlinkM startUpScript byte addrl byte addr2 4 Software Components 4 1 Proportinal Integral Derivative PID Controller We used a Proportional Integral Derivative controller PID controller to control the speed of our motor The output of our PID controller is more or less as follows u t Kp e t T Ki lout Ka Dout Here u t the output at time t in our case this is the output speed of our motor e t error at time t which is the difference between the two sonars in our case Kp proportional gain K integral gain Ka differential gain lout integral output the sum of all the errors from the beginning Dout differential output the rate of change of errors The variables affecting the autonomous control extended beyond the PID They were more or less as follows e Pre filter for sonar readings to PID input e PID update frequency e Post filter for PID output to motor input We found that our desire to have frequent PID updates was in conflict with three things The first two concern Dout The first is that a motor must be turned on for a minimum of about 500ms to give a useful impulse The second is that the platform rarely rotates through more than about a 1cm arc per 100mS at the position of the sonars so the value of
8. CSC 578C Project 1 Semi autonomous platform Alejandro Erickson Nathaniel Watt Rahnuma Islam Nishat 1 Introduction 2 Overview 2 1 PC 2 2 Base Station 2 2 Remote Station 3 Hardware Components 3 1 Power 3 1 1 Power Supply 3 1 2 7805 Voltage regulator 3 1 3 1 Mechanical Relay 3 1 3 2 Transistor 3 1 3 3 Diode 3 2 Motor and L298 driver 3 2 1 Pulse Width Modulation PWM 3 3 Two Sonars One Pin and a Special Wall 3 3 1 Hardware Interrupts and Timers 3 3 1 1 Alternative Approach Using pulseln 3 3 2 Corrugated Wall 3 4 Wireless Radio 3 5 Unfinished components 3 5 1 BlinkM LED and I2C 4 Software Components 4 1 Proportinal Integral Derivative PID Controller 4 2 Gamepad 4 3 Utilities 4 5 Wireless Radio 5 Lab Environment 5 1 Eclipse Software 5 2 Eclipsed by GNUmake 5 3 Some errors 5 4 Collaboration Tools 1 Introduction The project goal is to design a rotating platform that senses wall proximity and aligns itself autonomously This is phase one of a larger project to design an autonomous hovercraft that navigates through buildings There are two main learning objectives for this phase The first learning objective is to familiarize the team with the lab development environment and collaboration tools The second learning objective is to gain experience with a wide range of components Each component interfaces with the Arduino board through different protocols This project introduces UART A D SPI and 12C protocols 2 Overview
9. Kg does not accurately reflect the speed at which the platform is rotating Suppose the PID is updated every 100ms and the error term has increased by 1 for 500ms then the derivative value of the PID is Ka 1 for each reading We modified the PID to increase the memory of Dout so that it compares error terms that are five readings apart rather than one This helped give a greater longer impulse when the platform has rotated away from the wall for several readings Finally we wanted to avoid having and value that integrates over an infinite number of error terms Instead we saved 50 error terms in a buffer which updates in constant time The same buffer is used to access the 5 last error term to compute the above Dout term We found that 50 values causes too much overshoot however One solution we are discussing is reducing 50 to around 10 or maybe using an exponential decay for the integral output instead of summing up all errors in an array Implementing the latter is simple Instead of lout lourte t we would use lout C lourte t where O lt c lt 1 Therefore at time t k the weight of e t in the sum lout is C k e t 4 2 Gamepad Python code to read data from the USB gamepad on a windows machine was provided The program was written by River Allen and although it has some threading issues it works fairly well without modification User input consists of twelve buttons a directional pad and two analog sticks Each of the twelve
10. OR gate instead created from three NAND gates Note that P Q P amp P 8 Q amp Q where P and Q are signals from the sonar Here is the OR gate circuit We used the logic analyzer again to verify that the sonars wire signals were not interferering and that the interrupt pin was interpreting the pulses correctly Here Channels 5 6 7 are the same as before but Channel 4 is an output pin that is set high whenever the micro controller thinks it is measuring a pulse returning from a sonar Once again the trigger pulse and subsequent return high signal is seen in Channels 5 and 6 individually They are ORed to Channel 7 The micro controller knows to ignore the trigger pulse so only the return signals from each sonar are shown on Channel 4 4 Channel 4 5 Channel 5 Fes 6 Channel 6 7 Channel7 f 3 3 1 Hardware Interrupts and Timers The Arduino Uno with the ATmega328p micro chip has a 16 bit timer accessible through output pin 8 pin 14 on the chip This timer can be set to increment from 0x0000 to OxFFFF once every 1 2 8 64 256 or 1024 clock cycles By setting the right bits in certain registers the chip will accept interrupts on pin 14 in the form of either a voltage drop or rise called falling and rising edges at which point the contents of the timer register are copied into the input capture register ICR1 The interrupt can also trigger a software routine so that ICR1 can be used immediately T
11. at http nrqm ca mechatronics lab quide lab quide using the radio or the Arduino board data sheet Reading the data sheet explains SPI timings but Neil s guide is excellent for getting started 3 5 Unfinished components 3 5 1 BlinkM LED and I2C Due to time contraints we were unable to add BlinkM LEDs to our project Instead we made them work with a separate Arduino The BlinkMs are I2C devices meaning that each one has an address By giving each I2C device a unique address we are able to control many of them on the same two I2C pins of the Arduino board Roughly speaking the micro controller broadcasts instructions for an I2C device with a certain address All the I2C devices receive those instructions but they are only carried out by the one with the correct address Taking hints from Conyers et al we found that the Arduino has I2C pins and that the Wire h library is used to communicate with 12C devices Furthermore there is a library for the BlinkM LED that wraps the Wire h libary with nice commands The links we followed are given below e Conyers et al http webhome csc uvic ca mcheng 466 spring 201 1 handouts Sample 20Past 20Projects project1_awalker pdf Finding the I2C pins on the Arduino Uno http arduino cc en Main ArduinoBoardUno About the Wire h library http arduino cc en Reference Wire Examples using the BlinkM LED library http todbot com blinkm example_code Datasheet and resources for the BlinkMLED http
12. bytes read by the base station were a shifted version of what was expected to be received from the PC Initially we attempted to flush the serial connection before initializing transfer however this did not fix the error A simple work around for the problem is adding a flag byte to the begining of the bytes sent to the base station It is essential that the flag byte value never occurs in any of the actual data bytes that are sent Since the analog sticks have the largest range 100 100 any value outside of this is a valid flag byte When the base station reads a flag byte it knows it is synchronized with the bytes and the input can be passed to the remote station 4 3 Utilities Initially manual tuning of remote station PID settings required changing the hard coded settings recompiling the source and uploading to the Arduino board This is a very time consuming process and the settings must be tweaked constantly while finding values that perform well To make matters worse if the environment the remote station is operating in changes or the weight is added to the platform previously good values can become useless Looking ahead to the remaining phases of the project we decided that taking time to develop some helpful utilities in phase one will save countless hours later Using Python and TkInter we created a simple GUI terminal that is able to echo serial port data and live update the PID settings using the keyboard This interface allows our team t
13. ck feature Even if the auto ack is received this does not gaurentee that data has not been lost To handle this a simple master slave configuration with application level acknowledgements is suggested In our current phase the need for reliability is not high and therefore we decided to handle lost transmissions by repeating a command or just missing a data debug message This granularity was sufficient for this project Future projects will need a more robust system with reliability built into our communication The radio driver is straight forward to use Here is a code snippet to get the radio going void setup pinMode RADIO VCC OUTPUT digitalWrite RADIO VCC HIGH Radio Init Radio Configure Rx RADIO PIPE 0 host addr ENABLE Radio Configure RADIO 2MBPS RADIO HIGHEST POWER Radio Set Tx Addr DEST ADDR delay 250 It is important to define an I O pin for the radio Vcc This allows reseting the radio in software Without this the radio can get stuck when the board is reset but the radio isn t as the receive buffer can be full and block sending any packets Also this is very useful for handling radio errors One thing to be careful about is race conditions for the receive buffer This next snippet shows a potential fatal flaw for the radio if Radio Receive amp in packet RADIO RX MORE PACKETS rxflag 0 This code was
14. e intelligently interprets a special script for compiling projects in any language that can be compiled from the terminal and has been doing so since 1989 Learning GNUmake for this class will serve us in other projects relevant to our research much more than Eclipse can Furthermore the entire compilation procedure is visible at one time and a makefile can be copied from project to project without any difficulty Finally the editing of files can be done in our favourite source code editors rather than Eclipse which for one thing does not understand Vim or Emacs commands We found a few makefiles for arduino and the avr toolchain on the Internet but they all needed some modification which required an understanding of how a makefile is written The GNUmake documentation at http www gnu org software make manual make html is well written and the first few chapters help understanding the basic elements of the makefile For example a command looks like this target prerequisites recipe The target is an output file built from the prerequisites using the command line command in the recipe Typically these three elements are written with variables For example Compile create object files from C source files Cpp o CXX c ALL_CXXFLAGS lt o Here the first line is a comment and anything of the form is a variable defined somewhere in the makefile The two strings lt and are automatic variables inpu
15. eir are five pins on the relay two pins for the control circuit and three for the controlled circuit On the control side there is one pin on each side of a solenoid On the other side there is one ground one normally closed NC and one normally open NO pin When no current is passing through the solenoid the NC pin is short to ground When current is passing through the solenoid the NO pin is short to ground 3 1 3 2 CT 2N3904 Transistor A transistor is used in the control circuit to switch current through the solenoid on and off The collector is connected to one of the solenoid pins the emitter is connected to common ground and the base is driven by an I O pin on the Seeeduino When the I O pin is high the transistor allows current to flow through the solenoid This creates a magnetic field in the solenoid causing the mechanical switch to flip from NC position to NO position An alternative method for driving the control circuit is to remove the transistor and drive the relay Vcc directly with the I O pin While this is possible the amount of current used to drive the base is much less than the current required through the solenoid to trigger the relay switch Where Ic is the collector current and Ib is the base current and hef is the transistor gain Ic Ib hef which means the current used driving the base is a factor hef less than current through the solenoid Since the Seeeduino has limited total current output it is best to use a transisto
16. er It helped our understanding of makefiles however we did not have the cmake variant of make installed None of these worked perfectly so we wrote our own makefile from scratch First to familiarize ourselves with make but also to eliminate complications like support for assembly and listing files present in the above files Finally we needed to ensure that external libraries were being compiled correctly See the Appendix for our current makefile and commentary within it We expect to make some changes to this over the course of the semester 5 3 Some errors Here are a few errors and solutions When compiling error MCU atmega328p supported for assembler only This appeared because we were using avr gcc version 3 and should have been using 4 Run the command avr gcc version in a Mac OSX terminal to see the version and run avr gcc select 4 to select the 4 version Reference http www pololu com docs 0J31 all In the makefile Makefile 149 missing separator Stop make requires tabs in front of recipes but some programs replace tabs with spaces If this happens do a find and replace to go from 4 spaces or 8 or whatever the number is you find in front of the recipes to tabs Output from compilation error WProgram h No such file or directory error Wire h No such file or directory These will be followed by a string of errors every time you use something defined in those header files and it
17. f pulseln would not iterate during that time Furthermore if an edge was encountered during the interrupt then pulseln would not Know when it happened Alejandro made a forum post about it at http arduino cc forum index php topic 51632 msg371213 html msg371213 3 3 2 Corrugated Wall Finally we come to the accordion wall We found that the sonars gave unreliable readings when the platform was more than 15 degrees from the wall The sonar s range is so much greater than the distances we were measuring so we were able to disperse the return signal by making a corrugated wall pictured below This helped the sonars enormously So much so that the idea was adopted by several other groups in the class http www adafruit com blog 2009 06 23 getting started with the maxbotix sonar sensor quick start quide http www instructables com id Getting started with the Maxbotix sonar sensor q 3 4 nRF24L01 Wireless Radio The wireless radio is a Serial Peripheral Interface SPI device SPI consists of six pins used for control and communication The purpose of the pins and their connections to each of the arduino boards is given in the table below These connections are also shown in the schematics in the overview section eooo pooo CC m COM COI CEET The CE CSN and IRQ pins can be changed but the SCK MISO MOSI pins must be connected to the indicated pins for SPI to work correctly For more information check Neil s guide
18. hese registers and the bits that can be set are very carefully described in the long 566 page version of the atmega328p specifcations at http www atmel com dyn resources prod_documents doc8271 paf so we will focus on how to find the relevant information in that document a summary of this document is at http www atmel com dyn resources prod documents 8271S pdf The related specifications of for the Seeeduino s processor are available from the same website The registers relevant to the 16 bit timer are as follows TCNC1 This is a 16 bit timer register TCCR1B Timer Counter Control Register B This register has flag bits which determine the behaviour of the Timer and Input Capture behaviour These bits are named as follows o ICNC1 Input capture noise canceller This measures the voltage input at pin 14 on four consecutive clock cycles to ensure that a detected edge is not noise It is not always necessary to set this to 1 o ICES1 When this is set to 1 an interrupt is triggered on a rising edge and otherwise on a falling edge o CS12 C811 CS10 These bits control the frequency with which the timer TCNC1 is incremented prescaling e TCCR1A We set this to 0 to override an initialization by the Arduino library which uses this timer for PWM ICR1 This is the register to which TCNC1 is copied to when an interrupt is signalled TIMSK1 Timer Counter1 Interrupt Mask Register Setting the ICIE 1 bit to 1 enables interrupt capture for
19. ng first with different pin connections for example the enable pin E1 2 on the L298 was connected to the same pin as the LED to show us when the motor was supposed to be working To test the motor we ran the following code lude WProgram h lude avr interrupt h extern C void cxa pure virtual eir disable interrupts for do nothing until hard reset t pinEnablel 2 13 t pinll 12 E pind 11 void setup pinMode pinEnablel 2 OUTPUT pinMode pinI1 OUTPUT pinMode pinI2 OUTPUT void loop run at low speed in one direction for a time analogWrite pinEnablel 2 40 digitalWrite pinIl HIGH digitalWrite pinI2 LOW delay 3000 other direction digitalWrite pinIl LOW digitalWrite pinI2 HIGH delay 3000 stop analogWrite pinEnablel 2 0 delay 3000 int main void init setup for loop return 0 3 2 1 Pulse Width Modulation PWM Pulse width modulation is a technique to control the power to inertial electrical devices We have to send the signal to a device in our case the motor as a square wave Then we have to control the width of the square pulse A PWM signal is a square wave that occupies a certain percentage of the period with a high signal This percentage is called the duty cycle and it regulates
20. o quickly adjust PID settings while the platform is powered on making finding the critical values much easier Each time the settings are updated the PID calculation is reset and started fresh to avoid pollution from the previous error terms The real advantage of this terminal is continued development as the term progresses Adding features to remotely modify and debug the remote station will prove invaluable A major feature that is planned for project phase two is a live sensor data and PID error term plotter The plotter will graph and perform analysis on the actual sensor and control data live This gives our team much more precision than eyeballing what is occurring at the remote station or even using flat text to calculate oscillation periods Phase 3 plans include using the software to tune the PID automatically with no user input 4 5 Wireless Radio A driver and example code for the wireless radio is provided by Neil s lab guide This code is very clean and easy to understand The main task is to design what communication the base station and remote station need to handle Clearly commands from user input using the gamepad or utilities need to be passed to the remote station over the radio It is useful to have debugging information to flow from the remote station to the base station Wireless networking is particularly prone to data errors which must be handled in software The radio provides automatic retransmission attempts and an auto a
21. pping and causing a reset or other unexpected behavior The remote station is powered by the batteries that were provided in the lab and the base station is powered by USB from the PC Early experiments on the remote station used an AC adapter which converts wall power to 12v DC at 400mA measured at about 17v All power is regulated to 5v by an L298 for the motors and a 7805 for other components 3 1 2 7805 Voltage regulator Following simple instructions we managed to install a 7805 voltage regulator on our breadboard Regulated voltage measures at exactly 5 00 volts on the multi meter 1uF and 0 1uF capacitors are used in the following configuration Devices such as sonars can be connected from 5v out to the ground References http www tkk fi Misc Electronics circuits psu_5v html How capacitors work identifying the polarity http www tubelab com AssemblyManualSimpleSE Capacitors_SSE htm 3 1 3 Kill switch A kill switch provides the ability to shut down the motors though user input The switch consists of a mechanical relay transistor resistor and diode Some high level explanations of relay switches are available here e www autoshop101 com forms hweb2 pdf e http electronics howstuffworks com relay1 htm 3 1 3 1 SRD 5 105D Mechanical Relay A relay electrically separates two circuits This is used to separate a low power control circuit from the high power motor circuit The relay is a very simple device Th
22. r and use the battery to provide the current for the solenoid itself In our case the base current is only 2 44mA compared to a solenoid current of over 40mA to activate the switch 3 1 3 3 Diode A small diode is used to help dissipate the current spike after the magnetic field of the solenoid collapses This prevents damage to the transistor 3 2 Motor and L298 driver The platform is driven by two forward facing motors with fans Each one accepts values of 0 255 in analogWrite commands for pulse width modulation Running them one at a time gives sufficient impulse for our purposes Following the instructions in the L298 documentation and in Conyers Walker Warick http webhome csc uvic ca mcheng 466 spring 2011 handouts Sample 20Past 20Projects project1_awalker pdf we connected the battery power directly to the L298 and the motors In addition to the design in Conyers Walker Warick we added a kill switch connecting the L298 to ground As the motors are usually running we chose to enable power to the motors when the kill switch relay was in NC configuration This reduces the power used from the design of using the NO configuration to power the motors Using NO configuration would require current to flow though the solenoid and the base of the transistor when running the motors Since the motors are running more often than not it is a waste to use the NO configuration We made the following connections to the L298 We did some debuggi
23. radio Arduino board H bridge Relay Transistor three voltage regulators manual switch logic circuits battery power supply It is very important to balance the platform If the platform is unbalanced the platform does not align with the wall easily One difficulty came from an unbalanced platform settling in an unaligned position which forced the motors to realign the platform continuously To avoid this difficulty it is suggested to plan the layout of each component on top of the platform ahead of time Test the balance by holding the bottom of the hard drive casing while the platform is spinning Right Sonar 3 7432 78 E BT T pro Left Sonar 2n lr MM HE UU md Mega SE 3 Hardware Components 3 1 Power The remote station is powered by one 7V battery Components are isolated from each other using voltage regulators Not isolating the components can lead to unexpected transient bugs as components can interfere with each other This is particularly true with the motors which have a large power spike when starting up Power to the motors is regulated with the L298 H bridge Everything else is regulated through three 7805 voltage regulators A kill switch provides emergency motor stop functionality A manual switch controls power to all parts of the circuit 3 1 1 Power Supply Power to certain components especially motors is supplied from a source external to the Arduino board to prevent the voltage on the board dro
24. rally indicated by radiolnit failing to return Verify the problem using a multimeter before looking for software errrors 5 Lab Environment 5 1 Eclipse Software Eclipse seems to be the IDE of choice for the avr toolchain for most Arduino programmers Step by step tutorials for the project settings and installation are available at Neil s lab guide http nrgm ca mechatronics lab quide lab quide software environment The Arduino playground http www arduino cc playground Code Eclipse Some better instructions for Mac OS X http robertcarlsen net 2009 10 3 1 arduino in eclipse 989 Eclipse can be frustrating to first time users so we also used GNUmake See Section Eclipsed by GNUmake for an alternative 5 2 Eclipsed by GNUmake Eclipse is used in this course because it gives more control over source code and libraries than the Arduino IDE does however it carries several disadvantages Written in Java it does not run natively and hence feels foreign on most machines The instructions for configuring the avr toolchain on Eclipse require about ten different steps and nearly as many menus and windows Troubleshooting the configuration is cumbersome because each page in the project properties must be viewed separately and one cannot compare the properties of two projects without leaving the properties window and switching to that of the other project It is much more efficient and a more useful skill to use GNUmake GNUmak
25. t and output This recipe essentially tells the terminal to compile lt with the C compiler chosen in CXX and output to the file with flags defined in ALL_CXXFLAGS as well as c The Arduino IDE is updated frequently and the newest makefiles we found referred to the file structure in version 0017 and 0018 Furthermore not all makefiles are made for Mac OSX These are the major makefile projects we found From the arduino site and quite out of date Several makefiles were stems of this one http www arduino cc en uploads Hacking Makefile Two independent projects http mjo tc atelier 2009 02 arduino cli html http bleaklow com 2010 06 04 a makefile for arduino sketches html A github project that we found nearly by accident http blog codekills net archives 7 1 Makefile for Arduino 0017 html https gist github com 273821 A makefile for windows under cygwin http www tinymicros com wiki Makefile For Arduino Under Cygwin Windows About the AVR Toolchain http www nongnu org avr libc user manual index html Some explanation about libraries and archives http neather cs ucdavis edu matloff UnixAndC CLanquage Make html tth_sEc4 More explanation about compiling arduino from the command line http www sjbaker org wiki index php title Command_line Arduino Very granular explanation about the Arduino build process http arduino cc en Hacking BuildProcess A cmakefile was also provided to us privately by Paul Reim
26. the power output of a given pin The output pins with PWM control are marked on the Arduino boards and we used these to regulate power to the motor enable pin on the L298 using the command analogWrite Instructions for this function are at http arduino cc en Tutorial PWM If the period of the PWM is in the audible range of frequencies the motors will whine We changed the period by accessing the PWM registers as per the Lab TA s instructions 3 3 Two Sonars One Pin and a Special Wall Two forward facing sonars are triggered independently and their signals are read with a hardware interrupt pin and timer register on the micro chip When we chose the Seedstudio Ultrasonic Sensor SUS over the MaxSonar EZ1 MSE we thought our project would incur both an improvement in accuracy and in simplicity Ironically however the SUS s single signal pin proved to be much more headache than was intended We first used a pair of MSEs with a 7085 circuit powered by the 7 2V DC power supply Early versions of our software did not fire these independently instead we just allowed them to supply a constant stream of readings Although this did not cause any obvious collisions between sonar signals we knew that we were depending on luck to keep them from reading each others ultrasonic pulses The basics of this circuit is illustrated in the figure below Interpreting the input from the MSE Ar pin is easy with analogRead and the specifics are
27. timer 1 This configuration works as follows for the Arduino Uno On the ATmega328p ICP1 pin is called PBO 14 which is connected to output pin 8 of the Arduino Uno On the Seeeduino Mega ICP1 is available but not as an Arduino Mega pin Instead there is a direct connection to it at PD4 PD4 is an input pin by default but in case it needs to be accessed it s mode can be set with set PD4 pin to input DDRD amp BV 4 set PD4 pin to low IPORTD 8 BV 4 set PDA pin to high IPORTD BV 4 Last but not least the following should be included for these things to work include lt avr io h gt include lt avr interrupt h gt 3 3 1 1 Alternative Approach Using pulseln The Arduino library function pulseln purports to wait for a HIGH or LOW pulse on a given pin and return the length of pulse in microseconds It does do this but it freewheels the Arduino s CPU putting all other tasks on hold from when the function is called until the pulse is complete or it times out pulseln pin HIGH runs a loop to wait for the pin to go low then another to wait for it to go HIGH again and a third to measure the amount of time it is HIGH for and waits for a low It measures this time by counting the iterations of the last loop and multiplying it by the cycles per loop Suppose an interrupt was encountered during pulseln then the measurement would not account for the clock cycles used during the interrupt because the loop o
28. used on the provided debug server Looking closely however reveals that if an interrupt from the radio receiving a packet comes right before setting rxflag to 0 the software will never go receive the packet which in turn kills the radio as the buffer is waiting to be received from The only remaining changes are to add packet types to the radio h file and everything flows smoothly Misunderstandings regarding the supplied radio code cost more hours than was spent actually coding the modifications after the misunderstanding was cleared up There are two versions of the code currently available The USB drive at the front of the class does not contain the current version This caused hours of fixing the drivers provided from the USB drive The following day Neil clarified that the USB drive had not been updated and we threw out our changes switching to the new version supplied online The cost from this mistake continued when the familiarity with the initial code caused us to miss the define statement that was used to switch between the Seeeduino and UNO configurations With the software configuration still set to UNO the code was uploaded to the Seeeduino with of course the wrong pins being used The logic analyzer showed that the SPI signals were not correct but it still took a long time to find out why Another time consuming error was caused by losing connectivity through the hardware by wires breaking loose inside of the soldered headers This can be gene
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