A Low Cost Implementation of GPS Guided                        Driverless Cars           Ray-Shine Run                    ...
anything about that). Fortunately, a reflective photo interrupter                  case and could detect the Earth’s magne...
the correct decision of turning left or right when faces an                   component — 2.4GHz wireless transceiver. Fur...
x        ( x_tag     x_cur ) × d_LAT                                (1)        “touchdown” attained 100% when we set the r...
echo signal is proportional to the distance of the obstacle in                                            V.     CONCLUSIO...
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A low cost implementation of gps guided driverless cars


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A low cost implementation of gps guided driverless cars

  1. 1. A Low Cost Implementation of GPS Guided Driverless Cars Ray-Shine Run Jui-Cheng Yen Cheng-Yu TsaiDepartment of Electronics Engineering Department of Electronics Engineering Department of Electronics Engineering National United University National United University National United University Miaoli City, Taiwan Miaoli City, Taiwan Miaoli City, Taiwan rsrun@nuu.edu.tw jcyen@nuu.edu.tw mattbest1986@hotmail.comAbstract—The application of GPS is growing fast recently. Not B. Electronic & Electricalonly in military and science purposes, but also in civil use, GPSplays an important role in many electronic systems. For example, The abilities of moving agilely and positioning precisely arethe electronic navigation of automobile, the electronic map of two important objectives of a guidance system. Most of thePDA, etc. To deploy a research on this topic, we advise a low cost efforts have been focused on electronic and electrical issues.automobile GPS guidance system controlled by an 8-bit MCU The block diagram of the guidance system is shown in Fig. 2.(MCS-51), in which functions such as GPS guiding, obstacleavoidance, motion control and wireless communication areintegrated. Due to budget limit, we only accomplished the GPS ultra-sonic H-bridge module sensor driverprototype on a “toy car”. However, the experience of this projectencouraged us to go on for the next step. We hope to transfer the (moving)related technology to practical vehicle in the near future. electronic 8 - bit PWMKeywords – GPS; MCS51. compass MCU PWM I. INTRODUCTION H-bridge optical wireless The history of driverless car is over 30 years. The Line sensor driver transceiverTracing car, for example, has been used in automatic (turning)production lines for years. Meanwhile, the 2005 DARPAGrand Challenge and the 2007 DARPA Urban Challenge [7] Fig. 2. System block diagram of a guidance system.are two excellent driverless cars of the recent events. Theformer was definitely a Wild West adventure, whereas the III. SUBSYSTEMlatter was just like a road test for driver(less) license in A. Driving the dc motor : H-bridge driver + PWMmetropolis. Motivated by these models, we started this research.Although the gap (the level of technology and the scale of Since the toy car already has two small dc motorsbudget, etc) between the DARPA Challengers and our model is respectively for moving and turning, we only need to replacesignificant, there is one thing in common – Both receive the the drivers of the motors. The H-bridge seems to be the mostGPS signal from the satellites! Nevertheless, our model is popular approach for driving a dc motor. With proper PWMdefinitely a cost effective trial for the beginner. signals added to the inputs of the H-bridge driver, it is easy to implement speed- and direction- control on a dc motor. In this II. ARCHITECHTURE design, the PWM signals were generated by the MCS-51 based MCU (MPC82G516A). This enhanced version 8051 MCU hasA. Mechanical 6-channel embedded PWM outputs. The PWM function of Because of budget limit, we did not make a car especially MCU supports 8 bit resolution and programmable frequencyfor the project. As an alternative, we selected a suitable toy car (500Hz in the case). On the other hand, there are many optionsfrom the market. Basically, any kind of toy car which can move of H-bridge driver (ICs). We chose TA8249H IC as the driverforward/backward and turn left/right powered electrically is which has current capability up to 3A (average), thermalcandidate. Eventually, we bought a child-sittable toy car having shutdown, short current protection, and 4 modes of operationa maximum speed over 2m/s on a flat playground and a (forward / reverse / short brake and stop).maximum turning angle of the front wheel around 30°. Fig. 1shows the perspective and inside views of the toy car. B. Sensing the movements of car : homemade optical-rotary encoder There is no sensor on the toy car to detect the speed of car, so we adjust the duty cycle of PWM signal to execute the speed control. Basically, this approach worked well when the car moves on a flat surface. But, occasionally, the car stuck at some undetectable obstacles (such as small stones). Under this circumstance, even equipped with ultra-sonic sensor, the Fig. 1. Perspective and inside views of the toy car. system can do nothing but stuck there (the MCU does not know978-1-4244-5046-6/10/$26.00 c 2010 IEEE 1610 Authorized licensed use limited to: IEEE Xplore. Downloaded on March 05,2012 at 14:13:00 UTC from IEEE Xplore. Restrictions apply.
  2. 2. anything about that). Fortunately, a reflective photo interrupter case and could detect the Earth’s magnetic field and therebycan overcome the awkward situation. By a proper arrangement output the angle from North. Fig. 5 shows the concept ofnearby the rear wheel, the reflective photo interrupter will operation of the Compass Module, in which the x-axis of theoutput “on” whenever it is right above the reflective sticker, Compass Module indicates the long axis of the car body.otherwise it outputs “off”. Normally, when the car kept moving,the MCU will receive the frequent on/off signal from the photointerrupter. On the contrary, once the on/off signal stopped,meaning that the car was stuck, the MCU will increase the dutycycle of PWM signal to raise the output power of the motor.Usually, this is an effective approach for escaping the situation.Fig. 3 shows the concept of homemade optical rotary sensor.Actually, the frequency of on/off signal is almost proportionalto the speed of the car. So, the MCU can make a roughmeasurement of speed with this signal. Fig. 5. The concept of operation of HM55B. Obviously, it will be much easier to guide when the system reflective sticker combined GPS receiver with Compass Module; the concept of reflective photo interrupter the guidance is shown in Fig. 6 Consider the driverless car is at the origin, the angle (derived from GPS data) from North is 50°, and the angle (derived from Compass data) from North is 320°(clockwise). At the moment, there is no doubt that the driverless car should make a 90° right turn for the target. Actually, it is difficult for the driverless car to go strait exactly all the time. Therefore, after the right turn, the guidance system still need to adjust the steering wheel (changing the turning (a) (b) angle of front wheel) frequently before the car arrived at the Fig. 3. Homemade optical rotary encoder. (a) The reflective sticker on destination. This is consistent with the actual driving the wheel. (b) The reflective photo interrupter nearby the wheel. experience. Using the same type of photo interrupter and sticker, witha proper arrangement near the front wheel (see Fig. 4), the carcan make a null adjustment of forward direction before go strait. 0° target =320° =50° 270° 90° car Fig. 4. Homemade front-wheel null adjustment. Clockwise from North( 0°) 180°C. Guiding the car : GPS + Compass Module The GPS receiver definitely plays the most important role Fig. 6. The concept of guidance system.in the guidance system. The GARMIN 15-H module which Notice that the Compass Module is sensitive to any kind ofused in this case, receives (updates) the GPS signal from the magnetic field. Not only the Earth’s magnetic field, but also thesatellites. The information of the GPS signal will be extracted permanent magnet inside the dc motor will affect the sensor.by the module, and re-transmitted to the MCU through the Since there are two dc motors respectively the near front andserial port (RS232) once every second. Theoretically, the MCU rear wheels. Testing experiences indicate a minimum distancecan derive the distance (and direction) between driverless car of 30 cm between the Compass Module must be kept theand destination through a series of calculation based on the motor(s) is necessary; or, the sensor will lose the accuracy.GPS data. According to the result of calculation, the MCUcould make a decision for “where to go”. In practice, however, D. Obstacle avoidance : Ultra-sonic sensorthere would be difficult to guide the car with the GPS dataalone. Just imagine the following scenario: you are driving with Ultrasonic reverse parking sensor (subsystem) is almost aeyes closed, and the passenger tells you “the target is in the standard equipment of car in recent designs. Using the matureSouth-East direction, 100 meters away from here”. How can technology, the driverless car can avoid the detectable obstacleyou make the correct decision for turning left or right if you do during the process of guidance. What is detectable obstacle?not know the direction in front? Fortunately, a small Using the SRF05 ultra sonic module which has a 4 m range ofsemiconductor sensor can tell you the exact direction in front of detection, the driverless car can avoid the obstacle (e.g.,the car. The Hitachi HM55B Compass Module was used in the human) 1m in front with a cruising speed of 1 m/s. To make 2010 5th IEEE Conference on Industrial Electronics and Applicationsis 1611 Authorized licensed use limited to: IEEE Xplore. Downloaded on March 05,2012 at 14:13:00 UTC from IEEE Xplore. Restrictions apply.
  3. 3. the correct decision of turning left or right when faces an component — 2.4GHz wireless transceiver. Furthermore,obstacle, the driverless car has been equipped with two sets of combining with a homemade human interface which designedsensors near the headlights. By comparing the data of the two in Visual Basic 6, the GPS guidance system can conduct adifferent sensors, in general, it is easy to detect on which side plurality of cars simultaneously.the obstacle is (see Fig. 7a, Fig. 7c). However, when theobstacle is right in front (see Fig. 7b), there is no way to The IPro2.4GPM used in the case, is a highly integratedidentify the true situation (unless a visual sensor is used). multichannel RF transceiver designed for low-cost wirelessUnder this circumstance, the driverless car can only guess applications in the 2.4GHz Industry Scientific Medical (ISM)( e.g., always turn left). band. According to the specification of datasheet, the effective range of communication is around 500m for an open site test. So far we have test experiences within an 100m x 100m open area (the playground) only, and the quality of communication is perfect. (a) (b) (c) IV. RESULTS Fig. 7. Demonstration of different cases of obstacle. A. Experiments A C (language)-like statement that described the obstacle To verify the performance of the guidance system, we haveavoidance rule as shown below: made some experiments in a playground. The results from the experiments are described as follows.if ( d < 1m ) then //*stop back turn around{ Stop_and_Back(); 1) Accuracy: if ( (sensor_L) && (!sensor_R) ) turn_Right(); From a viewpoint of a software programmer, in order to else turn_Left(); know “where the car is”, we need to translate the GPS data} (string of character) into the value of longitude and latitude atelse if ( d < 1.5m) then //*decelerate and turn around first. The GPS receiver sends out many strings of character{ Slow_down(); every second (data updated each second). Each string is led by if ( (sensor_L) && (!sensor_R) ) turn_Right(); a “$” character. A typical string of GPS data is like this: else turn_Left();} ”$GPRMC,125031,A,2432.7581,N,12048.7789,E,000.0,000.0else if ( d < 2.0m) then //*turn around immediately ,150106,003.2,W*6B ”{ Continue; if ( (sensor_L) && (!sensor_R) ) turn_Right(); Obviously, each individual information (boldface) of the else turn_Left(); string is separated by a comma, we will focus on the three} items of information, its meaning explained as below:d obstacle distance 125031,A Greenwich Time 12 : 50 : 31 ( A : valid V : invalid )sensor_L the SRF05 on the left side: 1- echo, 0- no echo 2432.7581,Nsensor_R the SRF05 on the right side: 1- echo, 0- no echo Latitude 24°32.7581’ NStop_and_Back() the car must stop immediately, then move ( in the south hemisphere N S ) backward for 1m. 12048.7789,Eturn_Left() turn left Longitude 120°49.7789’ E ( in the west hemisphere E W )turn_Right() turn right When the satellite data is valid, GPS module outputs theE. Wireless communication : 2.4 GHz wireless transceiver time information with the status character of “A”, otherwise At first, we only preset one dedicated coordinate “V”. MCU can identify the status of GPS signal in the process(longitude and latitude) of destination into the flash memory of of navigation. Notice that, before making the mathematicalMCU, so, the driverless car can only execute a one-way (or operation on latitude and longitude, we must transfer characterround) trip. Although, it is not difficult to preset a set of type of latitude- and longitude- data into numerical type whichcoordinates for the car to make a multi-destination traveling. can be calculated legally in software program.However, it is still not flexible (smart) enough for easy use,because you have to shut down the power, and reprogram the There is an 100m race track in our playground, anMCU for each update of destination. To implement the excellent reference for testing accuracy. We have recorded thefunction of remote setting of destination, we have built a coordinates (GPS data) of Start- and End- of the race track,proprietary Master-Slave wireless LAN using the key then calculated the distance of the track by Equations 1-3:1612 2010 5th IEEE Conference on Industrial Electronics and Applicationsis Authorized licensed use limited to: IEEE Xplore. Downloaded on March 05,2012 at 14:13:00 UTC from IEEE Xplore. Restrictions apply.
  4. 4. x ( x_tag x_cur ) × d_LAT (1) “touchdown” attained 100% when we set the radius of the circle 5m. y ( y_tag y_cur ) × d_LON (2) B. Photos & Specifications z ( x2 + y2 ) 1/2 (3) Fig. 9 shows the circuit PCB we designed for the model. It is a 2-layor PCB with a size of 11cm x 5cm. The circuitx_cur, y_cur : latitude and longitude of current position comprises MCU, two H-bridge dc motor drivers, EIA-232x_tag, y_tag : latitude and longitude of target position driver for GPS receiver, 12V-5V DC regulator IC, two add-ond_LAT : effective distance per minute angle of latitude. sockets for Compass module and wireless transceiver. Thed_LON : effective distance per minute angle of longitude. PCB is powered by the DC 12V battery of the toy car.z : the distance of the race trackWe assume that the earth is a perfect sphere and that theaverage radius of the sphere is 6371 km. The d_LAT is around1853m/arcmin, which is a constant value over the world.However, the d_LON is not a constant and depends on latitude,and it can be calculated by Equation (4): d_LON d_LAT × cos(latitude) (4) Fig. 9. The PCB of the guidance system.For instance, the longitude and latitude of the playground(Miaoli city, Taiwan) is about 120.8°East, 24.5°North, and the Fig. 10 shows the wireless transceiver. To show its size,d_LON is 1686 meter per minute angle of longitude the radius of coin 1cm in diameter was placed adjacent to the(m/arcmin). Calculation of GPS data measured at the ends of circuit. The transceiver is supported by an SPI (Serialthe track showed below: Peripheral Interface) bus to interface with the MCU. It needs a DC 3.3V power.Start : 12048.7789 East / 2432.7581 NorthEnd : 12048.8327 East / 2432.7331 North x (32.7581 32.7331 ) arcmin × 1853 (m / arcmin) y (48.7789 48.8327 ) arcmin × 1686 (m / arcmin) z ( (46.331)2 + (-90.7068)2 ) 1/2 101.85 mThe accuracy is within 2 meters. Fig. 10. The IPro2.4GPM wireless transceiver. 2) Reliability: We have made many times of single target / one-way trip Fig. 11 shows the front view of the toy car. The arrowstest from different start points. Fig. 8 shows the concept of the indicate the ultra-sonic sensors fixed on the “bumper” beneathtest. the headlights. B ultra-sonic ultra-sonic A sensor sensor Fig. 8. Different routes for same target.The dashed circle of Fig. 8 stands for the target area. At first, Fig. 11. Front view of the car and ultra-sonic sensors.we set the radius of the circle 2m, the probability of“touchdown” was not 100%. In general, most of the tests (likecar A of Fig. 8) were successful in that the driverless car The left of Fig. 12 shows the HM55B compass modulearrived within the target area and stopped there, but, somehow, that communicates MCU through a 3-wire serial interface. Itsome failed. Like the car B of Fig. 8, they did not stop at the supports a 6-bit (64 direction) resolution for measurement andtarget but kept circling around the target area. We figured out needs a DC5V power. The right of Fig. 12 shows the SRF05that the cause is the limited stability of the GPS receiver. We ultra-sonic module. It starts a measurement of distance with athen enlarge the target area. Finally, the probability of trigger pulse (duration > 10us) generated by the MCU. The 2010 5th IEEE Conference on Industrial Electronics and Applicationsis 1613 Authorized licensed use limited to: IEEE Xplore. Downloaded on March 05,2012 at 14:13:00 UTC from IEEE Xplore. Restrictions apply.
  5. 5. echo signal is proportional to the distance of the obstacle in V. CONCLUSIONS front. The SRF05 can be triggered every 50ms, or 20 times A low cost GPS guidance system has been designed and each second. In this case, the MCU triggers the module at a implanted, in which the functions of guidance, obstacle rate of 10Hz. It also needs a DC 5V power. avoidance, and wireless communication for monitoring multi- car are realized. The budget for the working prototype is only US$300. The video of prototype can be viewed at website [8]. We believe that some mid range (less than 1km) transportation applications may adopt the experience of our model, for example, the shuttle bus in airport, the forklift in dock, etc. Actually, we are planning an extended application Fig. 12. The HM55B and SRF05. of this topic – the future parking lot (outdoor). Combining the GPS guidance system with the “automatic parallel parking Fig. 13 shows the GPS receiver and the attached antenna. system” (another concurrent research of our group), the The size of receiver module is around 4.5cm x 3.5cm. It is friendly parking management system can support a service supported by EIA 232 interface to communicate with the like this: The driver gets off (just leaves) the car after an MCU, and it can be powered by DC 8~40V (12V in this case). identification at the gate of the parking lot (something like “check in”), and the car will be guided to and parked at the assigned position by the smart system. Inversely, after an identification at the gate (something like “check out”), the whole thing rewind, and the car appears in front of the driver! REFERENCES [1] Sebastian Thrun, Mike Montemerlo, Andrei Aron, “Probabilistic Terrain Fig. 13. The GPS receiver and the antenna. Analysis For High-Speed Desert Driving”. [2] David Stavens, Gabriel Hoffmann, and Sebastian Thrun, “Online Speed C. Informations Adaptation using Supervised Learning for High-Speed, Off-Road Autonomous Driving”. [3] Tzuu-Hseng S. Li, and Shih-Jie Chang, “Autonomous fuzzy parking TABLE I. Car Specifications control of a car-like mobile robot”, IEEE Transactions on Systems, Man, and Cybernetics—Part A: Systems and Humans, Vol. 33, No. 4, July Physical 2003. Battery Length Width Height Weight [4] Tzuu-Hseng S. Li, Chih-Yang Chen, et. al., “Design and Implementation of Sensor Fusion Based Behavior Strategies for a Surveillance and 98.7 (cm) 51.3 (cm) 52 (cm) 9.5 (kg) 12 (V) , 2.3 (Ah) Security Robot Team”, in Proc. of SICE 2008, August 2008, Japan [5] K. Deergha Rao, ” An approach for accurate GPS navigation with SA”, TABLE II. Navigation Information Aerospace and Electronic Systems, IEEE Transactions on Volume 34, Issue 2, April 1998, pp. 695-699. Test Site [6] W. Holzapfel, M. Sofsky, U. Neuschaefer-Rube, ” Road profile Average Guidance recognition for autonomous car navigation and Navstar GPS support”, Speed Accuracy Aerospace and Electronic Systems, IEEE Transactions on Volume 39, Latitude Longitude Issue 1, Jan. 2003, pp. 2-12. 2432.7456North 12048.8058East 1 (m/s) 3~5 (m) [7] http://en.wikipedia.org/wiki/DARPA_Grand_Challenge [8] http://www.youtube.com/watch?v=_MOZg2gKyjc1614 2010 5th IEEE Conference on Industrial Electronics and Applicationsis Authorized licensed use limited to: IEEE Xplore. Downloaded on March 05,2012 at 14:13:00 UTC from IEEE Xplore. Restrictions apply.