ECE 477Digital Systems Senior Design Project9/12

Homework 5: Theory of Operation and Hardware Design Narrative

Team Code Name: Autonomous Rescue Vehicle (ARV)Group No. 10

Team Member Completing This Homework: _KrithikaK Iyer

E-mail Address of Team Member: kiyer @ purdue.edu

Evaluation:

SEC

/

DESCRIPTION

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MAX

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SCORE

1.0 /

Introduction

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5

2.0 /

Theory of Operation

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20

3.0 /

Hardware Design Narrative

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20

4.0 /

Summary

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5

5.0 /

List of References

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10

App A /

System Block Diagram

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10

App B /

Schematic

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30

TOTAL

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100

Comments:

Comments from the grader will be inserted here

1.0Introduction

The Autonomous Rescue Vehicle is a robot prototype that will detect the location of a lost person using Global Positioning System module, navigate to the location and bring the person back to safety, which we will assume to be the starting location of the robot. The person leaving the base station will be equipped with a GPS transmitter that will transmit the location of the person to the robot when in need. The GPS transmitter will use a GPS module to obtain the latitude and longitude of the person’s location andan RF transmitter module which will transmit the information. Using this information, the vehicle will autonomously route itself to the location. Three ultrasonic range finders (oneeach in the front, right and left side of the vehicle) will be used to avoid obstacles during the journey. 7.2V NiMH battery pack will be used to power the motors. Two 6V NiMH batteries will be used in series and regulated to +3.3V and -3.3 V to power the peripherals/modules as well as the battery monitoring circuit.

2.0Theory of Operation

The ‘Autonomous Rescue Vehicle’ can be subdivided into 8basic components:

  1. The microcontroller (PIC32MX120F032B)
  2. Motor drive
  3. Battery monitoring circuit
  4. GPS module (GP-635T)
  5. RF receiver module (XBP09-DPSIT-156)
  6. Ultrasonic Range Finder (MB1040)
  7. Power supply and voltage regulating Module
  8. Infrared Receiver (TSOP853)

The major components of the GPS transmitter are:

  1. The microcontroller (PIC32MX120F032B)
  2. GPS module (GP-635T)
  3. RF Transmitter module (XBP09-DPSIT-156)
  4. Power Supply voltage regulating Module

A 50 channel GPS smart antenna module (GP-635T manufactured by ADH Technology Co. Ltd.) will be used to obtain the geographical location of the person and the vehicle.It communicates with the microcontrollervia a serial UART at a baud-rate of 9600 bps.It sends/receives 8 data bits, 1 stop bit, with no parity bit. The GP-635T module supports 7 National Marine Electronics Association's NMEA-0183 sentence outputs. Our project will be using GPGGA - Global Positioning System Fix Data NMEA sentence which outputs the latitude, longitude, direction (North, South, East, and West), UTC time with an update rate of 1Hz, which will be sufficient for our purposes (our vehicle will travel at a max velocity of 5 miles/hr). The module will be powered with+3.3V during its active/normal mode of operation. The power consumption of the module in the normal mode is 56mA.APWR_CTRL input will be used to cut-off the power supply to themodule to reduce power consumption during stand-by.The GPS module will continuously track the location of the vehicle while it navigates. This data will be used to calculate the direction and distance to the final destination.

The location information obtained using the GPS module is transmitted from the person’s hand-held GPS transmitterto the rescue vehicle using aXBee-PRO® 900 OEM RF Module with a high gain antenna. This device has anoutdoor line of sight range of 6 miles. We will be using an antenna with gain of about 8.1dB, for reliable communication with minimal attenuation. The module uses 902-928MHz frequency band for communication with RF transmit/receive data rate of 157 kbps.The RF module will be interfaced with the microcontroller via the UART operating at baud rate of 9600bps. The RF module will input/output a 10 bit data including a start bit, 8 –bits of valid data, and a stop bit. We will operate the XBee module in the receive mode in the vehicle. The RF module will be set to cyclic sleep mode while the vehicle and the GPS transmitter are on standby. The module will be powered at an operating voltage of +3.3V.

Once the location of the lost person is identified using the GPSmodule and the RF module, the next major task in our project is to navigate the robot to the required location. 6 H-bridges and motors will comprise the motor drive module.The motor will be powered by a 7.2V unregulated supply. The three H-bridge on one side of the vehicle are connected with a single PWM output. Based on the duty cycle of the PWM, the motor speed will be varied. We will be varying the relative speeds of the wheels on either sideto steer the vehicle. The maximum speed of the vehicle will be 5 miles per hour. To save power we will operate the motor at 3 miles per hour.

The vehicle will be programmed to take the shortest route to its destination which will be a straight line path connecting its initial position to its final destination. The vehicle will almost certainly come across obstacle during its journey. Therefore, our project will be using threeLV-MaxSonar®-EZ4™ ultrasonic range finders (MB1040) to detect obstacle. The ultrasonic range finders will be placed at the front, right and left side of the robot.The LV-MaxSonar®-EZ4™ detects objects from 0-inches to 254-inches (6.45-meters) and provides sonar range information from 6-inches out to 254-inches with 1-inch resolution. The 0-6 inches will be indicated as 6 inches. The device will output this information as a voltage proportional to the distance to the nearest obstacle with a sensitivity of (Vcc/512V/inches). Hence, the device will be connected to the microcontroller’s ADC channel to continually obtain the information.The range finder will be powered at +3.3V.

The vehicle will be powered using two battery packs. One of them will be a 7.2V unregulated supply (Vdd as in Appendix B) for driving the motors. The other one will be two 6V batteries connected in series regulated down to +3.3V (Vcc as in Appendix B) and -3.3V (Vss as in Appendix B).The +3.3V will be used to power the microcontroller and all the IC and peripherals. The -3.3V will be used to power the opamp circuit used to monitor the battery level of the unregulated 7.2 V supply. The output of the battery monitoring module is sent to an analog input of the microcontroller.

The Infrared Receiver Module (TSOP853) sends a digital output to the microcontroller when it senses an Infrared signal from the remote. The operating voltage is 3.3V. This Module help to set the vehicle in active/stand-by mode.

The GPS transmitter will use only the 6V batteries connected in series regulated down to +3.3V and -3.3V. +3.3V will be used to power the microcontroller as well as the GPS and RF module in the GPS transmitter. The GPS module will be used with the same specifications in the GPS transmitter as well, in order to maintain the uniformity in the data used for calculations. The XBee will be operated in the transmit mode in the GPS transmitter. All other interfacing specifications of the RF module will be the same as in the vehicle.

All of the above 8 components of the vehicle and the 3 components of the GPS transmitter form the major subsections of our project and the proper functioning and interfacing of these subsection is critical to the success of our project.

3.0Hardware Design Narrative

The main subsystems of the microcontroller used are:

  1. PWM (Pulse Width Modulation)
  2. ADC (Analog to Digital converter)
  3. UART (Universal Asynchronous Receiver Transmitter)

Two UARTS in the microcontroller will be used. UART1 will interface with the GPS smart antenna module (GP-635T) and UART2 will interface XBee-PRO® 900 OEM RF Module (Appendix B).As can be seen in the schematics in Appendix B, pin 11 and 15 connects to the RTS and CTS control of the RF module respectively. These will be used as hand-shaking signals. The CTS provides an indication to the microcontroller to stop sending serial data to the module (in transmit mode) and RTS flow control allows the microcontroller to signal the module to not send data (in the receive mode).UART1 and UART2 will be programmed to operate at 9600 bps, 8-bit data, and no parity mode in order to synchronize with the operation of the UARTs in the GPS and RF module respectively. Pin 9 (digital output) will be used to control the operating mode (sleep/normal) of the GPS module (Appendix B). The GPS module and the RF Module will be interfaced the microcontroller in the GPS transmitter using similar connections and as the vehicle. The UARTs of the GPS transmitter will also be programmed to operate in the same mode as we are using the same GPS and RF module in the GPS transmitter as well.

Two PWM channelswill be used to control the wheels of the vehicle. One PWM channel will be connected to three H-bridges driving wheels on one side of the vehicle and the other PWM will connect to three H-bridges which controls the other side as can been seen in Appendix B. The PWM channels will output signal with varying duty cycle to the H-Bridges to control the speed of the motors.

The three ultrasonic range finders are interfaced with the microcontroller using 3 ADC’s (one for each range finder) AN11, AN12 and AN3(Appendix B).The AN3 will be used to connect to front sensor. The AN12 and AN11 are connected to the sensors in the right and left of the vehicle. These channels were chosen for convenience with the positioning of the sensors. The three ADC channels will receive voltage inputs from the sensors proportionalto the distance to theclosest obstacle. Readings can occur up toevery 50mS, (20-Hz rate). The three ADC channels will programmed to operate in the fractional 16-bit format

Pin 6 of the microcontroller will be used as an ADC to obtain the level of the battery. As this analog input reduces below a certain threshold the battery life will be determined as critical. The ADC will be operated in Fractional 16-bit mode.

0.1 µF ceramic capacitors with a resonance frequency of 20MHz will be used as decoupling capacitors. Moreover, in order to maintain power supply stability, our project will use filter capacitors of 2.2 µF and 10µF.We will be using ceramic bypass capacitors of about 10µF.

Summary

The Autonomous rescue vehicle will use 2 Pulse Width Modulation, 2 Universal Asynchronous Receiver Transmitter, 3 Analog to Digital Conversion Peripheralsand Digital I/Os in the microcontroller to interface with the 8 modules. The GPS transmitter will use 2 Universal Asynchronous Receiver TransmitterandDigital I/Os in the microcontroller to interface with the GPS and RF modules.A 7.2 NiMH battery pack powers the motors while two 6V batteries are used to power the rest of the modules. The GPS and RF modules are interfaced through the UARTS, the motors through the PWM. The ultrasonic sensors use the ADC channels. Ceramic capacitors are used for decoupling and bypassing. All these modules will be used constructively to realize our goal of building a prototype of an autonomous rescue vehicle that will obtain the location of a lost person, navigate to the location without colliding with any obstacle and bring the person back to safety successfully.

4.0List of References

[1]MaxBotix Inc. “LV-MaxSonar –EZ4” Available:

[2]ADH Technology Co. Ltd. “Data Sheet/GP-635T”. [Online] Available:

[3]Digi International Inc. “XBee-PRO 900/DigiMesh”. Available:

[4]Pololu Robotics & Electronics. “Rechargeable NiMH Battery Pack: 3.6 V, 2200 mAh, 3x1 AA Cells, JR Connector”. Available:

[5]Pololu Robotics & Electronics. “Rechargeable NiMH Battery Pack: 6.0 V, 2200 mAh, 5x1 AA Cells, JR Connector

[6]Microchip. “PIC32MX120F032B Datasheet”. Available:

[7]Vishay Semiconductors.“IR Receiver Modules for Remote Control Systems. Available:

Appendix A: System Block Diagram

Appendix B: Schematics

Autonomous Rescue Vehicle


GPS Transmitter Schematic

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