T-106.530 Embedded Systems Project work hardware description
Contents
1. 000 000 Figure 13 Tachometer PCB Component bottom layout 27 Bumper software puskuri c Improved IR sensor bumper implementation for Project Work Car Helsinki University of Technology Department of Computer Science Laboratory of Software Technology Course of Embedded Systems Version 0 2 Jaakko Ala Paavola 2006 02 05 Notice There is a bug in the bumper PCB layout Infrared LED and corresponding indicator LED are swapped in position Theory of operation Ambient interference compensation Each sensor is measured twice Once with IR illumination led on and once without IR light Values are subtracted to remove the affection of ambient light Low pass filtering KF Minor errors are filtered by averaging For each bit last FILTER_COUNT 10 measurements are summed together The must be at least FILTER THRESHOLD 3 values exceeding THRESHOLD value for the bit to be interpreted as one Extended validity The is a black out gap in between sensors In order not to loose Signal immediately the last non zero value is considered good for VALID_COUNT 10 rounds until the value is cleared include lt avr io h gt include lt avr signal h gt include lt avr interrupt h gt include puskuri2 h 28 define TEST MODE ifdef TEST MODE define MUX BA2. KF Minor errors are filtered by averaging For each bit last FILTER_COUNT 10 measurements are summed together The must be at least FILTER THRESHOLD 3 values exceeding THRESHOLD value for the bit to be interpreted as one Extended validity The is a black out gap in between sensors In order not to loose Signal immediately the last non zero value is considered good for VALID_COUNT 10 rounds untill the value is cleared ifndef __PUSKURI_H define __PUSKURI_H define THRESHOLD 0x30 define FILTER_COUNT 10 define FILTER_THRESHOLD 3 define BIT_COUNT 8 define VALID_COUNT 10 Hardware definitions define LED_PORT PORTB 32 define LED_DIR DDRB define LINE PORT PORTD define LINE_DIR DDRD define PULSE_PORT PORTC define PULSE DIR DDRC define PULSE_IN PINC define PULSE PIN PC7 endif Makefile Helsinki University of Technology T 106 530 Embedded systems AVR GCC Makefile FOO OC GO 2k 2k 2k 2k k 2k 2k 2k SUFFIXES SUFFIXES 5 o cof elf eep rom define some variables based on the AVR base path in AVR cc avr gcc AS avr gcc RM rm f RN mv CP BIN avr objcopy ELFCOF avr objdump ELFCOF objtool INCDIR all other steps compile ok then echo Errors Necessary for AVR Studio to understand that everything went ok DONE
3. 2 90 49192151 7 y 1no 98192 ano ANI 9NI sino SNI vino ano INI ano 2 2 5 19 1541 ds sino vino Y 100 Ira 90 euno auno Lino 1 9 9 1 2001 Cd LLNI vadalar Sadtv 9091900 1091200 1992501 08d DIXI 54 6 00 94 4900 193999 V 91W53WN pi jutod 1045 Fano H3MOd 125 Bumper schemati Figure 4 22 Sal cad moh ocamo Figure 5 Bumper PCB Top copper layer Figure 6 Bumper PCB Bottom copper layer a E iv 001 n o o Ho o j 089 o o i o 2 uon zu o 5 218 won o szu E 5 P 695 001 a o o Bad o o A E Jews A o 5 u S ou 962 5 E 2 e Fari MENT a Song Le og 10 e 9 99 oz 69 o 9 9 o 9 6 5 9 5 pe o 9 S 96 9y 9IVO3W 3609
4. 15 4 32 MGU bOaE ae oa ae he ede Se S 15 431 Schematics 15 4 3 2 Connectors 16 AA Tachometer 17 441 Requirements aoaaa a 17 4 4 2 Mechanics i2 1c oo 17 4 4 3 Schematics and circuit board 18 AAA QonnectorS eom ew RT 18 445 18 5 Software 20 5 11 pumper code ong 24 BGA wees Bee A 20 5 2 Main control code 20 6 Conclusions 21 6 1 21 IR Bumper B Tachometer C Bumper software D MCU board 22 25 28 36 1 Introduction The goal of the project is to provide students hands on experience in pro gramming embedded systems The project work is part of the basic course of embedded systems at Helsinki University of Technology Students attend ing the course are expected to have basic skills in programming C C language 1 1 Assignment task In the project work a group of students should create a program for an autonomous model car to drive a tracked marked by reflective tape in the floor The car has an infrared sensor system to detect the position of the tape referred to the car The program controls steering and speed of the car in order to drive the track round as fast as possible without loosing the track 1 2 Back
5. o amp om of d k E EN 09 o o 9o 89 me D 4 o TIN 9 99 6092 uam 0 xu ay o 9 e Ho B omo o 679 lsu od 69 E E o o E o de mou g m o o o 089 001 24 037 e e Figure 7 Bumper PCB Component top layout 23 o o a 2 7 9 a o 9 6 8 B F o a ame 8 8 5 5 5 a a a o e 5 o o E ERR o E o o o o o o o o o 00000 00000000 00000 00000 oe 00000000 00000 Figure 8 Bumper PCB Component bottom layout 24 T T 19945 92 20 22 9002 20 71 eq iueunoo oye 371 YaLAWOHOVL WszvPog qNszreda Ens i i in el I SO 4 Y OAY3S Figure 9 Tachometer schematics 25 Figure 10 Tachometer PCB Copper top layer Figure 11 Tachometer PCB Copper bottom layer 26 R10 p Hi RT POWEF R19 PULSE70 ae lt i e o 8 Figure 12 Tachometer PCB Component top layout O O O O O O O O O
6. multi master collision prevention The bus is originally designed for inter ic within a single system or circuit board With short cables a it i possible to use the bus without any additional arrangements With longer cables several meters a special impedance con verter and or reduced clock speed is required The specified standard max imum speed for the bus is 400 kHz which is well enough to deliver bumper data frequently enough 4 2 3 Mechanics It is reasonable to keep the mechanical design of the bumper as simple as possible KISS theorem The simplest way yet robust enough is to stack a sandwich by placing the circuit board in between two transparent plastic Plexiglas plates and bolting them together as shown in upper picture of figure 3 As all the components are surface mounted the whole circuit board remains thin and the thickness of the bumper remains in less than 15 mm In the way the circuit board and components are well protected yet allowing the infra red sensor system working and keeping debugging indicator LEDs well visible 7 UPPER PROTECTIVE PLEXI TOP SIDE COMPONENTS 74 CIRCUIT BOARD BOTTOM SIDE COMPONENTS 7 LOWER PROTECTIVE PLEXI BOLTS 7 UPPER TRANSPARENT PLEXI TOP SIDE COMPONENTS CIRCUIT BOARD IR SHIELD PLATE OPTIONAL LOWER PLEXI Figure 3 Mechanical structure side view The problem of the design are direct IR beams from a transmitter to a receiver In
7. 0 0 EEPROMFORMAT lt 0 elf eep add your projects below this defines the aims of the make process all puskuri clean RM rom eep cof RM RM elf RM 1st RM map test puskuri puskuri rom puskuri cof DONE puskuri elf puskuri o puskuri o puskuri c puskuri h 35 D MCU board Figure 14 Embmega32 board layout 36
8. echo Errors none default mcu type MCU atmegai6 default compiler flags ahlmsn CPFLAGS g Os funsigned char funsigned bitfields fpack struct fshort enum s Wall Wstrict prototypes mmcu MCU Wa ahlmsnd c 1st 33 default assembler flags ASFLAGS mmcu MCU Wa mmcu MCU gstabs default linker flags LDFLAGS W1 Map lt o map cref mmcu MCU output format can be srec Motorola ihex Intel HEX ROMFORMAT srec EEPROMFORMAT ihex AVR Studio needs Intel HEX format compile instructions to create assembler and or object files from C source C 0 ho 4c CC c CPFLAGS I INCDIR lt o 0 he CC s CPFLAGS I INCDIR lt o 0 assemble instructions to create object file from assembler source ho 48 AS x assembler with cpp ASFLAGS I INCDIR c lt o echo Error target 0 not defined in Makefile exit 1 link instructions to create elf output file from object files helf o CC LIB LDFLAGS o 0 create AVR Studio cof file from elf output file and map file Acof helf ELFCOF loadelf mapfile elf map writecof 0 create flash and eeprom bin file ihex srec from elf output file Arom Welf BIN 0 ROMFORMAT R eeprom 0 helf BIN j eeprom set section flags eeprom alloc load change sect 34 ion lma
9. 106 530 Embedded Systems Project work hardware description Helsinki University of Technology Jaakko Ala Paavola March 26th 2006 Version 1 0 Abstract This document describes the new hardware platform of the student project work assignment of the course of Embedded Systems at Helsinki University of technology 1 0 06 03 26 JAP Initial version Contents 1 Introduction 4 1 1 Assignment task 4 12 Background 4 2 Requirements 5 3 Platform 6 31 RC I10 mechanics e db RP UE CR 6 3 2 Steering and driving 6 33 Powersouree 6 4 Hardware 7 41 Block diagram 1 0 0 00 0000000000 7 4 1 1 Microcontroller unit 7 4 122 NEBOT ux ome x e deeem en ue ue IU 8 8 41 3 Control 3 um nc rte A de Ry 8 414 9 41 5 9 4 2 IR sensor bumper 9 42 1 Requirements 10 4 2 2 Design rationale 10 4 273 Mechanics itg 5 5 oet AR eb Si 12 AD As 42 yn Atl IE Re Re 13 4 2 5 via ker ae pk Ox oo 3o so 9 k 13 4 2 6 ConBnecLorg Gey vu 14 Design Haws uw x ee
10. Ambient interference compensation Each sensor is measured twice Once with IR illumination led on and once without IR light Values are subtracted to remove the affection of ambient light Low pass filtering Minor errors are filtered by averaging For each bit last FILTER COUNT 10 measurements are summed together The must be at least FILTER THRESHOLD 3 values exceeding THRESHOLD value for the bit to be interpreted as one Extended validity The is a black out gap in between sensors In order not to loose signal immediately the last non zero value is considered good for VALID COUNT 10 rounds until the value is cleared 5 2 control code No ready made code is provided for the MCU of the car as it is students task to implement a control code 20 6 Conclusions At the moment of writing this document the hardware is in use by students executing the course project work Consequently no final conclusions of the success of the project can by drawn yet First versions of schematics and PCB of bumper and tachometer con tains some errors None of these errors are fatal or show stopper thus the hardware can be used with minor work around All subsystems of the car are tested and functioning properly A simple test code using all the functions is implemented to demonstrate usability of the system There is no reason to believe that the project will fail in a sense of students not learning programming embedded systems In any
11. for the Embmega32 is presented in table 4 3 2 The cable has four series re sistors 100 1k ohm It is compatible with UISP and AvrDUDE programming softwares in DAPA direct access mode D25 ISP 1 Strobe 470 ohm 6 SCK 2 Data 0 470 ohm 2 MOSI 11 Busy 470 ohm 4 MISO 16 Init 470 ohm 8 RST 19 Ground 10 GND Table 8 MCU board ISP programming cable 4 4 Tachometer Tachometer provides rotation feedback for motor control 4 4 1 Requirements The same basic requirements apply to the tachometer robust mechanics reliable electronics and inexpensive components High accuracy is not a critical issue It is enough to get more than one pulse per rotation It is not necessary to determine the direction of rotation One should know the direction anyway 4 4 2 Mechanics Due to the mechanical structure of the car it is not feasible to attach the tachometer directly to the motor Instead it is much easier to mount it to the wheel axle Due to the planetary gear of the transmission the tachometer 17 does not indicate exact rotation speed of the motor There may occur minor error when the car is turning or tires are slipper The sensor of the tachometer consist of infra red optical sensor and per forated disk The disk has six holes thus six pulses are available per full rotation of the tire Interval between pulses represent distance of apx 3 1 mm Due to the nature of the tachometer the ap
12. lt FILTER COUNT if filter pos amp 1 bitno average tt if average gt FILTER_THRESHOLD value 1 lt lt bitno else value amp 1 lt lt bitno If null value from sensors maintain old value for VALID_COUNT times if value 30 LINE_PORT value valid_count 0 else if valid_count gt VALID COUNT LINE_PORT 0 LINE_PORT value bitno 0 if bitno 7 amp amp value 0 LINE_PORT value endif Prepare new concersion Turn on next led LED PORT 0x80 gt gt bitno Set MUX ADMUX MUX_BASE bitno state 0 else state diff ADCH LED_PORT 0 turn led off for reference measurement state 1 Trigger new conversion ADCSRA _ BV ADSO puskuri h Improved IR sensor pumber implementation for Project Work Car 31 Helsinki University of Technology Department of Computer Science Laboratory of Software Technology Course of Embedded Systems Version 0 2 Jaakko Ala Paavola 2006 02 05 Notice There is a bug in the pumber PCB layout Infrared LED and corresponding indicator LED are swapped in position Theory of operation Ambient interference compensation Each sensor is measured twice Once with IR illumination led on and once without IR light Values are substracted to remove the affection of ambient light Low pass filtering
13. case the hardware is far more better and suitable for the course than the old one 6 1 Future improvements If new releases are introduced design flaws in bumper and tachometer circuit board should be fixed Primarily this includes fixing pin order of connectors and adding protective series resistors in signal lines Possible future enhancement would be telemetry application transmit ting real time data from the car to a PC over wireless RF link Additional sensors for safety and status information would be nice Ultrasonic or in frared proximity detectors would help prevent accidents with solid objects wall human leg etc Reliable odometer would improve capability of learning the track It first round the car records track features and then it can drive faster as it can pre empt coming cources It is possible to do that with the current tachometer but reading are not very accurate tires may slip With acceleration sensors it would be possible to determine wether the car is moving as indicated by tachometer 21 Bumper T T 19945 9 20 70 600790727 2 0 iueunoo Q e tanysnd 1971 VIOAVWd V1V BONAIOS ONISS32OHd NOLLVIAHOJNI JO A90 1ONHO31 30 ALISHAAINN DINIS T3H Quigeisl lU ano ino 91 819 Lp gt 00 1no PF Liu 95192 7 Y ino WIZ aga ls Y 100
14. other purposes Thus the controller must have four ports ATmegal6 and ATmega32 controllers offer required I O capacity One port is equipped with multiplexed 10bit AD converter These two chips have identical pin configurations only the amount of memory differs 16kB of flash program memory in the ATmegal6 and 32kB in the Mega32 Thus the choice is just a matter of taste In order to make it possible to run more complicated software in the future it is vice to choose the bigger one There are other versions like ATmega48 that offer enough I O pins just for the main operation 8 bit transmit led output 8 pin receiver analog input and 8 bit external IO However there are no extra pins available for any additional functionality like simultaneous serial communication or extra indicator LEDs Thus favoured choice is a bigger controller like the 16 A T mega series of microcontrollers have internal calibrated RC oscillator to provide clock source for the controller The frequency of the oscillator is 10 not exact there is variance of few percent depending on operation tem perature and voltage Maximum clock frequency with the internal oscillator is 8 Mhz The application is not timing critical The limiting factor is the speed of the AD conversion and that s well below the speed of the controller computational core Thus the code will spend greater deal of the time just waiting for finalisation of the AD conversion Internal
15. sensor of the system that tells about the external word The are other sensors like tachometer but they tell about the car itself Thus the IR sensor is the most important one and the car can do nothing without it Figure 2 IR sensor system The bumper as number of infrared transmitter receiver pairs parallel in front of the car as shown in figure 2 If there is reflective tape below the receiver the reflection of the IR light is higher and the receiver gets stronger signal compared to plain flooring 4 2 1 Requirements The IR bumper has following special requirements e mechanically robust structure e electrically reliable single PCB high quality manufacturing e bumper width conforming with the width of the car body e many enough IR transmitter receiver pairs e active electronics with on board microcontroller e analog sensor measurement parallel I O output signal ON OFF e serial bi directional communication e visible light indicator LEDs for IR transmitters and receivers e software adjustable parameters threshold etc in circuit programmable 4 2 2 Design rationale Microcontroller Atmel 8 bit AVR microcontroller family is the controller of choice The controller must have three full 8bit I O ports for sensor operation one port for IR led control output one port with AD conversion for IR sensor and one port for parallel I O with main system In addition some extra pins are required for serial communication and
16. shops with just basic parts included 3 2 Steering and driving Steering is based on standard servo motor which is controlled with normal servo control signal The DC main driving motor is controlled with RC car motor controller unit which is controlled with servo signal Middle value represents neutral and difference either forward or backward proportionally In the middle section there is quite a noticeable neutral zone cab to prevent un intendent movement 3 3 Power source The car is equipped with a regular RC car battery back Seven cell NiMH or similar rechargeable power unit 4 Hardware 4 1 Block diagram The block diagram of the car hardware is presented in figure 1 LCD DISPLAY SERIAL PORT Heli i lol 7 TACHOMETER PB7 9 7 2 9 PD1 0 969 UART PD PD4 PDS STEERING SERVO x DRIVE MOTOR lt gt gt gt SERVO CONTROCEER gt lt c INFRA RED SENSING PUMBER Figure 1 Block diagram of the car hardware 4 1 1 Microcontroller unit The heart of the car is AVR ATmega32 microcontroller The AVR microcon troller family is based on 8 bit RISC architecture with 32 general purpose registers The ATmega32 can run up to 16 MIPS at 16MHz It has 32 kB program flash memory 2kB RAM memory and 1 EEPROM memory Peripheral features includes 3x Timer Counter 8x 10 bit AD converter 4x PWM USART module UART SPI 120 and
17. the lower picture of figure 3 the problem is solved by placing a 12 drilled non transparent plastic plate in the bottom side of the PCB There are holes drilled in the place of transmitter and receiver components No other components are placed in bottom side The non transparent plexi acts as IR radiation shield preventing direct beams from transmitter to receiver At the same time it narrows the angle of transmitter and receiver subsequently decreasing interference between transmitter receiver pairs 4 2 4 Schematics Schematic diagram of the IR bumper is presented in appendix A In the left side of the diagram is the ATmegal6 microcontroller chip with it s supply voltage circuits The zero ohm resistor RO provides single point of connection in between digital and analog ground Inductor L1 and capacitor C13 provides high frequency interference pro tection by low pass filtering for analog supply voltage Vdd A D converter of the ATmegal6 is fed by that voltage In addition analog supply is delivered for infrared receiver circuits Connectors are located in the bottom of the diagram There are 2x8 pin data connector 2x5 pin in system programming connector ISP and 2x5 pin JTAG connector Connector pinouts are detailed in section 4 2 6 In the middle of the diagram are indicator LEDs and their driver circuits ULN2803A octal darlington transistor array located A single I O pin of the AVR microcontroller can source or sink up to 40mA
18. Ds LED T0 LED T7 are in wrong order Actual IR transmitter LEDs are correct but visible light indicator LEDs are swapped 4 3 MCU board The main MCU board of the car is a ready made industrial controller unit Embmega32 from Ere Co Ltd Thailand http www ere co th Manufacturer describes the board as follows EMBMEGA32 is an embedded microcontroller board based ATMEGA32 AVR microcontroller family It is low cost and flexible making it ideal as an embedded controller Normal speed of board is 16MHz and 14 7456 MHz The board has 4 ports 32 I O lines mini buzzer reset switch and one RS232 port Also it has two options one is serial eeprom 24XX family and is real time clock 051307 with 3 volt lithium battery The board has connector for common character module with contrast pot power supply and current limit resister for backlight All ports on the board are connected to IDC connectors but ADC connec tions are available using terminals PCB is a two layer with design intended for demanding industrial applications The board provides 10 pins serial ISP header for hooking up to ISPAVRP2 which download a code to the board without a flash programmer 4 3 1 Schematics Schematic diagram is presented in the Embmega32 schematics data sheet and user manual 15 4 3 2 Connectors Connector placement is presented in appendix D IO Port the four I O ports of the AVR are available via 2x8 pin conn
19. GND 6 D2 PD2 7 SCL PCO 8 D3 PD3 9 SDA 10 D4 PD4 11 PC6 12 D5 PDS 13 PC 7 14 D6 PD6 PD7 Table 2 bumper data connector In system programmin The in system programming connector ISP conforms with Atmel s STK200 development board The connector pinout is presented in table 4 2 6 1 MOSI 5 2 3 4 GND 5 RST 6 GND SCK 8 GND 9 MISO 10 GND Table 3 bumper ISP connector JTAG The JTAG programming and in system debugging interface con nector conforms with Atmel s AVR JTAG connector The connector pinout is presented in table 4 2 6 1 2 2 GND 3 TMS 4 4 5 6 RST 7 8 9 TDI PC5 10 Table 4 bumper JTAG connector 14 4 2 7 Design flaws The first version of the bumper electronics has a few design flaws e Analog reference voltage of the AD converter of the AVR is connected to analog ground Should be left open or have a capacitor inbetween At board assembly the wire must be cut off e Data and JTAG connectors are missing protective series connector In the car assembly these are mounted in the cable connecting the bumper to the MCU board e Data connector pins are swapped compared to pin order of the MCU board connector 1 and 2 are swapped and so on The cable must fix the problem by swapping corresponding signals e Transmit indicator LE
20. SE BV REFS1 _BV REFSO _BV ADLAR 2 else define MUX BASE BV REFS1 _BV REFSO BV ADLAR endif unsigned unsigned unsigned unsigned unsigned unsigned unsigned unsigned int main char char char char char char char char bitno 0 pulsecount 0 state 0 diff 0 value 0 filter FILTER COUNT filter pos 0 valid count 0 void Initialize 1 0 LED DIR LED POR LINE DI LINE PO T R RT Oxff All output 0x80 First LED on Oxff All output 0x00 All signals low Initialize ADC ADMUX MUX BASE Internal 2 56V reference right adjusted ADCSRA BV ADEN ADC Enabled BV ADSC Start conversion BV ADIE ADC interrupt enabled _BV ADPS2 Prescaler 16 Global interrupt enable seiO return 0 SIGNAL SIG ADC unsigned char average pos 29 Read the sensor value and set line signal if state diff ADCH ifdef TEST_MODE if bitno 3 LINE_PORT diff else Set value into filter bit matrix if diff gt THRESHOLD LINE_PORT line_bit filter filter pos Ox01 lt lt bitno else LINE PORT amp line bit filter filter pos amp 0x01 lt lt bitno Compute filter averages if bitno gt BIT COUNT 1 if 4 filter_pos gt FILTER COUNT filter pos 0 for bitno 0 bitno lt BIT COUNT bitnot 4 average 0 for pos 0 pos
21. are available in SMD versions in cluding microcontroller IR emitters and receivers and passive components resistor capacitor In fact IR receivers are already purchased in SMD components TAOS TSL261RD Monolithic Silicon IC Containing Photo diode Operational Amplifier and Feedback Components The component is equipped with Visible Light Cutoff Filter Plastic to improve tolerance against ambient light sources The center frequency of the receiver is 940 nm infra red Serial communication Bi directional serial communication path does not only allow reading of analog measurement values but makes it possible to set parameters of the bumper sensing on fly by the main controller board The ATmega series of microcontrollers has built in hardware support for traditional serial port RS 232 TEA 232 I2C bus and SPI bus Serial port is the most traditional one However lack of natural framing support makes it hard to design robust communication protocol The SPI is very has and 11 reliable but it has other limitations I2C is considered as the best choice for the serial communication I2C is a synchronous multi node multi master bus with addressing and frame support There is a clear start and stop condition for each data frame and designer does not need to develop an upper layer protocol to implement a robust communication protocol The bus is synchronous and always clocked by the current master There is also a arbitration mechanism
22. current but several such currents at the same time exceeds the total current specifications of the controller Thus all indicator LEDs and infrared LEDs are driven by darlington transistor buffers In the right side of the schematic diagram are located infrared transmitter LEDs and receiver circuits TSL261RD Light to voltage optical sensor with their analog supply voltage filters Each receiver circuit has a low pass RC filter to prevent any interference from other parts of the system Analog output signals are delivered to A D converter of the AVR 4 2 5 Circuit board The printed circuit board of the bumper has total dimensions of 205 x 65 mm The board is double sided with through hole copper The board is covered with protective green epoxy solder mask Images of board copper layers and component layouts are presented in appendix A Most of the components are located in the top side of the board only IR transmitters and receivers are located in the bottoms side and two resistors which didn t had convenient place in the top side Circuit boards are manufactured by Futurlec Inc in Thailand http www futurlec com 13 4 2 6 Connectors Data The bumper data connector includes 8 bit parallel bus and serial I2C bus In addition there are two extra bits for interrupt and other purposes The pinout of the connecter is presented in table 4 2 6 15 16 D7 1 GND 2 DO0 3 GND 4 D1 5
23. ectors All the connectors have the following pin order 1 0012 GND 3 D1 4 GND 5 0216 GND D3 8 GND 9 D4 10 GND 1 05112 GND 13 06 14 GND 15 16 Table 5 MCU board IO port connectors LCD display The LCD display connector interfaces an industry standard Hitachi HD44780 character dot matrix LCD display driver in 4 bit mode However the R W bit of the interface is not connected thus one can not poll the status of the busy flag of the display Instead a delay interval long enough must be implemented in the software 1 5V 2 GND 3 RS 4 5 6 GND 7 GND 8 GND 9 GND 10 GND 1 05 12 D4 13 D7 14 D6 15 BL 1 BL Table 6 MCU board IO port connectors Pin 15 and 16 provides voltage for LCD display back light There is no series resistor in this power supply thus there must be a resistor with suitable value in the display component if back light is used ISP The in system programming connector of the Embmega32 has a pin order which is totally incompatible with any de facto standard pinout An 16 adapter cable custom made programming cable is required to program this device The pin order of the connector is presented in the table 4 3 2 1 2 MOSI 3 4 MISO 5 6 SCK 7 8 RST 9 Vcc 10 GND Table 7 MCU board ISP connector Wirings for very simple custom made parallel port connected ISP cable
24. er full rotation of tire approx once every 3 cm The pulse frequency from the tachometer is so low that one can not calculate pulses per time unit but one must calculate time units between pulses Use of the feedback tachometer is important in order to implement efficient and accurate control algorithm for the car 4 1 3 Control The car has driving motor and steering servo Both devices are controlled with standard servo control signals PWM There is no feedback from the steering servo but the steering can be expected being accurate enough The control of the driving motor can not be considered proportional The power fed to the motor does not correlate well with speed acceleration There are factors like charge of batteries current speed etc that affects 4 1 4 User interface The user interface of the car consists of 12 button keybad and 16x2 characters LCD display The display is based on standard Hitachi HD44780 driver Note that even if the LCD module is standard it is not connected into the microcontroller in conventional way Read Write signal is not connected Thus one may not apply most AVR LCD libraries available in the net 4 1 5 Computer interface The computer interface of the car consists of in system programming inter face and serial interface One may connect personal laptop or other gadget into the serial port and tune parameters collect statistics etc 4 2 IR sensor bumper The IR sensor bumper is the only
25. ground The course had similar project work assignment previously However hard ware platform caused plenty of problems Cars were mechanically fragile and electrically unreliable Some of the subsystems didn t worked at all like tachometers Exercising with such a hardware is a frustrating and discour acing experience that does not cause further interest in embedded systems The old version of the hardware was designed at Tampere University of technology and they offered a new design However they price request for the stuff was so high that it was considered feasible to design a hardware of our own and maintain some hardware knowledge of our own Mechanical basis of the old hardware was decided to reuse which decreases expenses 2 Requirements The are a few principal non functional requirements for the design of the new car e robust mechanical structure e reliable electronics easy maintenance with replaceable parts inexpensive components Of course the car has certain functional requirements as well e completely independent no external guidance adjustable speed both direction e speed feedback e steering with no direct feedback e sensor system that can detect tape track e simple user interface with input and output e in system programmable logging option 3 Platform 3 1 RC 10 mechanics The mechanical basis of the hardware is a standard RC 10 radio controlled model car platform They are sold in hobbyist
26. many more The microcon troller has in system programming function the internal program memory can be programmed via serial programming interface while the microcon troller is mounted in the embedded hardware Pin configuration of the AVR ATmega32 is described in table 4 1 1 PIN BIT s Dir Description PA 7 0 in Infra red sensing bumper PB 7 0 in out Keybad 7 out LCD data 3 6 out LCD data 2 5 out LCD data 1 4 out LCD data 0 PC 3 out LCD enable PC 2 out LCD register select PC 1 0 in out 12 bus not in use PD 7 6 Not in use PD 5 out Steering servo PD 4 out Drive motor control PD 3 Not in use PD 2 in Tachometer PD 1 0 in out Serial port Table 1 AVR pin assignment 4 1 2 Sensors The main sensor of the car is the infra red reflection sensing bumper The bumper has 8 parallel IR transmitter receiver pairs each controlled indi vidually by the peripheral microcontroller of the bumper The IR receiver provides analog voltage proportional to the intensity of received IR light Depending on the value it is possible to determine whether there is reflective tape or plain flooring in beneath of the sensor The bumper provides 8 bit parallel signal each bit corresponding to one detector pair The value of the bit is high if the reflection is above certain threshold value otherwise low The driving motor has feedback tachometer sensor The sensor provides 6 pulses p
27. oscillator can be con sidered good enough for the application in question Analog measurement In the old bumper there was only available a digi tal ON OFF signal per detector indicating wether a reflection strong enough was detected or not For just the car application only that is sufficient to do the job However it is reasonable to make it possible to use more complicated sensing algorithms later on By providing analog reflection illumination mea surement value per each detector and propably cross detector it is possible to implement much more accurate positioning of the reflective tape track In addition such an analog measurement allows calibration of sensor threshold and other parameters on fly In beginning of each race the team can calibrate the bumper to the current ambient illumination conditions in order to decrease false detections In a broader sense it is wise to make the bumper as modular as possible to make it possible to use the bumper in other appliances as the RC car Or use it with different kind of track With analog measurements the bumper can detect differences in surface reflection related to colour or material of the surface tiled flooring in order to navigate Thus the bumper can easily be adopted in other robotic solutions as well Surface mount components In order to improve the endurance of the device it is better to have no components sticking out of the board Most of the components required for the device
28. plication software can not count pulses per time unit but it must count time unit between pulses 4 4 3 Schematics and circuit board Schematic diagram and circuit board layout of the tachometer are presented in appendix B The circuit consists of infrared sensor connectors and servo signal indicators There are three dummy connector pads for signals which are currently not in use 4 4 4 Connectors 1 GND 2 3 GND 4 5 GND 6 Tachometer PD2 ExtInt0 7 8 Spare PD3 9 GND 10 Servo 1 PD4 OC1A 11 GND 12 Servo 2 PD5 OC1B 13 GND 14 Spare PD6 15 Vec 16 Spare Table 9 Tachometer connector Tachometer connector 1 Signal 3 GND Table 10 Servo connector Servo and spare signal connectors 4 4 5 Design flaws The first version of the tachometer circuit has a few design flaws 18 Tachometer connector has pins in wrong order Pins 1 and 2 are swapped and so on This must be fixed by a cable that swaps the pins correspondingly e Tachometer signal is missing protective series resistor 19 5 Software 5 1 Simple yet functional bumper code is presented in appendix The code switches one IR LED on at a time and measures corresponding analog signal level to determine wether predefined threshold value is exceeded The code has some improvements as defined in file header Theory of operation
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