F13: Line Following Robot

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Grading Criteria

  • How well is Software & Hardware Design described?
  • How well can this report be used to reproduce this project?
  • Code Quality
  • Overall Report Quality:
    • Software Block Diagrams
    • Hardware Block Diagrams
      Schematic Quality
    • Quality of technical challenges and solutions adopted.

Line Following Robot

Abstract

The Line Following Robot detects a black line on a white surface and moves forward following the line. If a black line is not detected, the Line Following Robot moves forward searching for a black line to follow. Once the Line Following Robot detects a black line, it will begin following the black line.

Objectives & Introduction

Objectives

The objectives of the Line Following Robot include:

  • Move forward searching for a black line on a white surface.
  • Detect a black line on a white surface.
  • Generate control commands to follow a detected black line.

Introduction

In order to follow a black line on a white surface, the Line Following Robot interfaces the NXP LPC1758 microcontroller on the SJ One Board with a Reflectance Sensor Array and Dual Serial Motor Controller. The block diagram below illustrates the connectivity of these primary components. The diagram also illustrates the connectivity between the Dual Serial Motor Controller, two brushed DC motors, twin motor gearbox, and two tires.

Block Diagram for the Line Following Robot

The LPC1758 microcontroller acquires sensor data from the Reflectance Sensor Array, generates motor commands to steer the Line Following Robot based on the sensor data, and transmits the motor commands via a serial communication interface to the Dual Serial Motor Controller. Upon receipt of the motor commands, the Dual Serial Motor Controller provides the appropriate PWM control signals to the brushed DC motors to steer the Line Following Robot. The process of obtaining sensor data from the Reflectance Sensor Array and transmitting the corresponding motor commands to the Dual Serial Motor Controller repeats at a 20 Hz rate.

Reflectance Sensor Array

The Reflectance Sensor Array includes eight sensors. Each of the eight sensors consists of an IR LED, a phototransistor, and a capacitor connected in series with the phototransistor. To obtain a reflectivity reading from the Reflectance Sensor Array, the microcontroller GPIO pins connected to the sensor I/O pins are driven high to charge the capacitors. Once the capacitors have been fully charged, the microcontroller switches its GPIO pins to inputs. With the microcontroller GPIO pins switched to inputs, the capacitors begin discharging through the phototransistors at a rate based on the reflectivity of the surface illuminated by the IR LEDs. After allowing an appropriate amount of time for the capacitors to discharge accordingly, the eight sensor I/O pins of the Reflectance Sensor Array are read by the microcontroller.

A white surface has a high reflectivity and will turn the phototransistor on. When the phototransistor is turned on, the capacitor in series with it will be allowed to discharge through the phototransistor. With the capacitor discharged, a low voltage will be present at the sensor I/O pin and will be converted as a logical zero by the microcontroller. In contrast, a black surface has a low reflectivity and will not turn the phototransistor on. When the phototransistor is off, the capacitor in series with it will not be allowed to discharge through the phototransistor. As a result, a high voltage will be present at the sensor I/O pin and will be converted as a logical high by the microcontroller. Thus, sensors detecting a white surface will return a logical zero and sensors detecting a black surface will return a logical one when the microcontroller reads the Reflectance Sensor Array.

Sensor Data Analysis

After obtaining a reflectivity reading from the Reflectance Sensor Array, the microcontroller analyzes the data to determine the appropriate motor command to be sent to the Dual Serial Motor Controller. If none of the eight sensors detect a black line, a move forward command is sent to the Dual Serial Motor Controller to continue searching for a black line to follow. A move forward command is also sent to the Dual Serial Motor Controller if either of the two or both of the middle sensors detects a black line. When any of the three sensors on the left side of the Reflectance Sensor Array detect a black line, the Dual Serial Motor Controller is commanded to turn left towards the line. Similarly, if any of the three sensors on the right side of the array detects a black line, a turn right command is sent to the Dual Serial Motor Controller.

Dual Serial Motor Controller

The Dual Serial Motor Controller accepts commands via its serial communication interface using a baud rate between 1200 and 19200 with eight data bits, no parity bit, and one stop bit. Its serial interface is receive-only and automatically detects the baud rate. The UART2 peripheral of the microcontroller is configured to transmit the generated motor commands to the Dual Serial Motor Controller at a baud rate of 9600.

Upon receipt of a motor command, the Dual Serial Motor Controller adjusts its PWM motor control outputs to perform the commanded action. The PWM motor control outputs operate at a frequency of 600 Hz and the voltage level is based on the input motor voltage supplied to the Dual Serial Motor Controller. The PWM motor control outputs provide independent control of two brushed DC motors. The independent control of the two motors allows the Line Following Robot to turn left or right using a ball caster as the third point of balance.

Power

Power for the Line Following Robot is provided by four AA batteries contained in an enclosed battery holder with an included power switch. The four AA batteries generate 6.0 volts which is routed as the motor input voltage to the Dual Serial Motor Controller, the input voltage to the 5.0 V Step-Down Voltage Regulator, and the input voltage to the 3.3 V Step-Down Voltage Regulator. The regulated 5.0 volts is routed to the SJ One Board via a modified USB Mini-B cable. The SJ One Board further regulates the 5.0 volts to 3.3 volts for use by the LPC1758 microcontroller and the other components on the board. The 3.3 V Step-Down Voltage Regulator output is routed to both the Reflectance Sensor Array and the Dual Serial Motor Controller.

Team Members & Responsibilities

  • Kurt Breault II
    • Hardware Design
    • Driver Development
    • Software Design
    • Integration and Test
    • Project Documentation

Schedule

The proposed schedule lists the tasks to be completed each week. The time frame for each task spans from a Wednesday to the following Tuesday. This time frame format was selected to facilitate project progress discussions with the professor at the end of each weekly lecture held on Tuesday.

Week Date Proposed Schedule Actual Schedule
1 10/02 to 10/08 Write project proposal. Begin ordering components.
  • Project proposal written, submitted and approved.
  • Placed order #1 with Sparkfun.
  • Placed order #2 with Pololu.
2 10/09 to 10/15 Finish ordering components.
  • Placed order #3 with Pololu.
3 10/16 to 10/22 Generate proposed schedule. Begin mechanical layout of components. Begin electrical layout of componets.
  • Generated proposed schedule.
  • Began mechanical and electrical layout of components.
  • After beginning the mechanical and electrical layout of components, realized another order was required to obtain additional mounting components.
  • Placed order #4 with Pololu.
4 10/23 to 10/29 Complete mechanical layout of components. Complete electrical layout of components.
  • Continued mechanical and electrical layout of components.
  • Encountered issues routing wires from the IR LED Reflectance Sensor Array to the SJ One Board due to physical limitations.
  • Reprioritized the mechanical and electrical layout of components to be an ongoing task throughout the duration of the project.
5 10/30 to 11/05 Interface SJ One Board with IR LED Reflectance Sensor Array.
  • Resolved issues related to routing wires from the IR LED Reflectance Sensor Array to the SJ One Board.
  • Continued mechanical and electrical layout of components.
  • Completed initial driver revision for the IR LED Reflectance Sensor Array and interfaced it with the SJ One Board.
  • Tested the IR LED Reflectance Sensor Array driver by passing the array over a black line on a white background and verifying the individual sensors of the array reported the correct readings.
6 11/06 to 11/12 Interface SJ One Board with Dual Serial Motor Controller.
  • Continued mechanical and electrical layout of components.
  • Completed initial driver revision for the Dual Serial Motor Controller; however, the Dual Serial Motor Controller was not interfaced with the SJ One Board because the required mechanical and electrical infrastructure has not yet been completed.
  • Tested the generation and transfer of motor controller commands by looping back the UART2 TXD2 pin to the UART3 RXD3 pin. The UART2 TXD2 pin will be used to connect to the Dual Serial Motor Controller serial receive input pin. The UART3 RXD3 pin was configured to support motor controller command generation debug efforts. Motor controller commands transmitted on the UART2 TXD2 pin and received on the UART3 RXD3 pin were read from the UART3 receive FIFO and printed to the Hercules serial console to verify their validity. The proper initialization of the UART2 TXD2 pin for serial communication with a 9600 baud rate, 8-bit data, no parity bit, and one stop bit was also verified.
  • Began integrating and testing the IR LED Reflectance Sensor Array driver with the Dual Serial Motor Controller driver by passing the array over a black line on a white background, generating the appropriate motor controller command to steer the center of the array over the black line, transmitting the generated command on the UART2 TXD2 pin, receiving the transmitted command on the UART3 RXD3 pin, printing the received command to the Hercules serial console, and verifying the printed command indicates the expected action based on the sensor array reading.
7 11/13 to 11/19 Begin integration and test of SJ One Board, IR LED Reflectance Sensor Array, and Dual Serial Motor Controller.
  • Completed mechanical and electrical layout of components.
  • Began integration and test of SJ One Board, IR LED Reflectance Sensor Array, and Dual Serial Motor Controller.
  • The Dual Serial Motor Controller had to be reconfigured to its default configuration of two-motor control with motor numbers two and three. It is unknown whether the Dual Serial Motor Controller was delivered in a non-default state or if initial integration and test efforts corrupted the default configuration.
  • The pull-down resistor value for the Dual Serial Motor Controller reset input pin was changed from 4.7 kOhms to 1.0 kOhms in order to produce an appropriate low voltage value.
  • The GPIO pin used for reset control to the Dual Serial Motor Controller was changed from pin P2.9 (RXD2 on the SJ One Board) to pin P1.22 due to the pull-up resistors and LED connected to the RXD2 signal line of the SJ One Board. The Dual Serial Motor Controller was stuck in reset prior to the change of pins used.
  • The “move forward” function for the Dual Serial Motor Controller had to be modified to send separate control commands for the left and right motors with the same speed setting. The original version of the function sent one control command intended for both the left and right motors; however, a single command sent for both motors was not functioning as described in the Dual Serial Motor Controller User’s Guide.
8 11/20 to 11/26 Complete integration and test of SJ One Board, IR LED Reflectance Sensor Array, and Dual Serial Motor Controller.
  • Completed integration and test of SJ One Board, IR LED Reflectance Sensor Array, and Dual Serial Motor Controller.
  • Refactored the source code to provide separate .cpp and .h file pairs for drivers and utilities. Previously, all of the code was contained in a single main.cpp source file.
  • Began generating figures to be included in the project report.
9 11/27 to 12/03 Demonstrate project. Write project report.
  • Generated the line following course to be used during the demonstration of the Line Following Robot.
  • Recorded the presentation and demonstration of the Line Following Robot to be viewed in class on 12/03.
  • Continued generating figures to be included in the project report.
  • Began writing the project report. The project report deadline was extended to 12/07.
10 12/04 to 12/07 Complete project report.
  • week 10, row 3

Parts List & Cost

The table below summarizes the parts used and the cost for the Line Following Robot project.

Qty Item Description Manufacturer Manufacturer Item No. Vendor Vendor Item No. Cost Total Cost
1 SJ One Board (LPC1758) SJSU N/A SJSU N/A $75.00 $75.00
1 QTR-8RC Reflectance Sensor Array Pololu 961 Pololu 961 $9.95 $9.95
1 Pololu Low-Voltage Dual Serial Motor Controller Pololu 120 Pololu 120 $39.95 $39.95
1 Pololu 3.3V, 600mA Step-Down Voltage Regulator D24V6F3 Pololu 2106 Pololu 2106 $5.95 $5.95
1 Pololu 5V, 600mA Step-Down Voltage Regulator D24V6F5 Pololu 2107 Pololu 2107 $5.95 $5.95
2 Pololu Robot Chassis RRC01A Transparent Gray Pololu 250 Pololu 250 $5.95 $11.90
1 Tamiya 70097 Twin-Motor Gearbox Kit Tamiya 70097 Pololu 61 $12.00 $12.00
1 Tamiya 70144 Ball Caster Kit (2 casters) Tamiya 70144 Pololu 66 $5.99 $5.99
1 Tamiya 70101 Truck Tire Set (4 tires) Tamiya 70101 Pololu 65 $4.80 $4.80
1 4-AA Battery Holder, Enclosed with Switch N/A N/A Pololu 1159 $1.75 $1.75
4 AA Alkaline Battery Panasonic - BSG LR6XWA/B Digi-Key P646-ND $0.35 $1.40
1 170-Point Breadboard (Red) N/A N/A Pololu 1491 $2.95 $2.95
1 USB Cable A to Mini-B, 6 ft N/A N/A Pololu 130 $2.49 $2.49
1 0.100" (2.54 mm) Breakaway Male Header: 1x40-Pin, Straight, Double-Sided N/A N/A Pololu 1065 $1.49 $1.49
3 0.100" (2.54 mm) Shorting Block: Red, Top Closed N/A N/A Pololu 971 $0.19 $0.57
1 Ceramic Capacitor 6-Pack 0.1uF 50V N/A N/A Pololu 1165 $0.99 $0.99
1 Stranded Wire: Black, 22 AWG, 50 Feet N/A N/A Pololu 2640 $5.00 $5.00
1 Stranded Wire: Red, 22 AWG, 50 Feet N/A N/A Pololu 2642 $5.00 $5.00
1 Stranded Wire: White, 22 AWG, 50 Feet N/A N/A Pololu 2649 $5.00 $5.00
1 Female Crimp Pins for 0.1" Housings 100-Pack N/A N/A Pololu 1930 $5.95 $5.95
2 0.1" (2.54mm) Crimp Connector Housing: 1x1-Pin 25-Pack N/A N/A Pololu 1900 $0.59 $1.18
1 Resistor Kit - 1/4W (500 total) N/A N/A SparkFun COM-10969 $7.95 $7.95
1 0.100" (2.54 mm) Breakaway Male Header: 1x40-Pin, Straight N/A N/A Pololu 965 $0.99 $0.99
1 Aluminum Standoff: 1" Length, 2-56 Thread, M-F (4-Pack) N/A N/A Pololu 1944 $1.59 $1.59
1 Machine Screw: #2-56, 1/4" Length, Phillips (25-pack) N/A N/A Pololu 1955 $0.59 $0.59
1 Machine Hex Nut: #2-56 (25-pack) N/A N/A Pololu 1067 $0.99 $0.99
1 Machine Washer: #2 (100-pack) B&F Fastener Supply FWSS 002 Digi-Key H733-ND $3.36 $3.36
1 Machine Washer: #4 (100-pack) B&F Fastener Supply FWSS 004 Digi-Key H734-ND $3.48 $3.48
1 Tamiya 70164 Universal Metal Joint Parts (4pcs) Tamiya 70164 Pololu 90 $3.90 $3.90
1 Aluminum Standoff: 1-1/4" Length, 4-40 Thread, M-F (4-Pack) N/A N/A Pololu 1951 $1.99 $1.99
1 Aluminum Standoff: 3/4" Length, 4-40 Thread, M-F (4-Pack) N/A N/A Pololu 1949 $1.59 $1.59
1 Machine Hex Nut: #4-40 (25-pack) N/A N/A Pololu 1068 $0.99 $0.99
1 Machine Screw: #4-40, 5/16" Length, Phillips (25-pack) N/A N/A Pololu 1961 $0.69 $0.69
4 Aluminum Standoff: 3/8" Length, 6-32 Thread, F-F Keystone Electronics 2209 Digi-Key 2209K-ND $0.40 $1.60
1 Machine Washer: #6 (100-pack) B&F Fastener Supply FWSS 006 Digi-Key H735-ND $3.66 $3.66
1 Machine Screw: #6-32, 1/4" Length, Phillips (100-pack) B&F Fastener Supply PMSSS 632 0025 PH Digi-Key H708-ND $6.54 $6.54
1 Machine Screw: #6-32, 3/8" Length, Phillips (100-pack) B&F Fastener Supply PMSSS 632 0038 PH Digi-Key H710-ND $8.10 $8.10
1 Scotch Removable Mounting Squares, 1" x 1", 16 ct. Scotch N/A Amazon N/A $7.99 $7.99
1 Crimping Tool: 0.1-1.0 mm² Capacity, 16-28 AWG N/A N/A Pololu 1928 $34.95 $34.95
1 ST-1 Mini Diagonal Cutter N/A N/A Pololu 159 $3.99 $3.99
1 ST-2 Mini Long-Nose Pliers N/A N/A Pololu 150 $3.99 $3.99
1 Paladin Tools 1118 GripP 20 Wire Stripper/Cutter, 30-20 AWG Greenlee Communications PA1118 Digi-Key PA1118-ND $17.33 $17.33
Total Cost $321.52

Design & Implementation

The design section can go over your hardware and software design. Organize this section using sub-sections that go over your design and implementation.

Hardware Design

The hardware design of the Line Following Robot is separately described in terms of routing power and signals. The routing of power and signals is considered separately to simplify their description and associated diagrams.

Power Routing

Power for the Line Following Robot is provided by four AA batteries. The four AA batteries are installed in an enclosed battery holder that includes a power switch. The power switch on the enclosed battery holder is used to power the Line Following Robot on and off. When the power switch is set to the on position, the four AA batteries provide +6.0 V.

The +6.0 V provided by the four AA batteries is routed to the VMOT input of the Dual Serial Motor Controller. The VMOT input of the Dual Serial Motor Controller provides the raw motor voltage used to control the brushed DC motors via its PWM motor control outputs. The +6.0 V provided by the four AA batteries is also routed to the VIN inputs of the 3.3V Step-Down Voltage Regulator and 5V Step-Down Voltage Regulator. These connections and the other power routing connections of the Line Following Robot are illustrated in the figure below.

Power Routing for the Line Following Robot

The 3.3V output of the 3.3V Step-Down Voltage Regulator is routed to VCC inputs of the Reflectance Sensor Array and the Dual Serial Motor Controller to provide the logic voltage for these devices. The 5V output of the 5V Step-Down Voltage Regulator is routed to the +5V input of the USB Mini-B connector on the SJ One Board via a modified USB Mini-B Cable. The SJ One Board routes the 5V input voltage to its own internal voltage regulator to supply 3.3V to the on-board LPC1758 microcontroller and other on-board devices. Although the SJ One Board provides its internally generated 3.3V as an output for peripherals, the SJ One Board 3.3V output could not be used due to the current draw on the 5V Step-Down Voltage Regulator and its associated dropout voltage.

The distribution of power for the Line Following Robot is accomplished via the breadboard power routing connections illustrated in the figure below. In addition to the previously described routing of power, both the 3.3V Step-Down Voltage Regulator and 5V Step-Down Voltage Regulator require their active-low SHDN inputs to be tied to their 3.3V and 5V outputs, respectively. These connections are made on the 170-point breadboard via shorting blocks, a.k.a. jumpers, as depicted by the red rectangles in the breadboard power routing connections diagram.

Breadboard Power Routing Connections for the Line Following Robot

The 1.0 kOhm pull-down resistor for the active-low RST input of the Dual Serial Motor Controller is also illustrated in the breadboard power routing connections diagram. The pull-down resistor is required in the event the microcontroller itself is reset. When the microcontroller is reset, its pins are switched to inputs and no longer provide the intended control for the Dual Serial Motor Controller. The pull-down resistor overrides the floating input condition and asserts reset to the Dual Serial Motor Controller to ensure the motors do not keep running while the microcontroller is recovering from reset.

Signal Routing for the Line Following Robot
Chassis, Assembled Gearbox with Tires, and Ball Caster
Assembled Chassis with Gearbox, Tires, and Ball Caster
Battery Holder (4-AA with Switch) and Breadboard (170-point)
Assembled Chassis with Battery Holder, Breadboard, Headers, and Jumpers
Assembled Chassis and Brushed DC Motors with Capacitors and Wires
Assembled Chassis with Brushed DC Motors
5V Step-Down Voltage Regulator, Dual Serial Motor Controller, 3.3V Step-Down Voltage Regulator, and Pull-Down Resistor
Assembled Chassis with 5V Step-Down Voltage Regulator, Dual Serial Motor Controller, 3.3V Step-Down Voltage Regulator, and Pull-Down Resistor
Reflectance Sensor Array, Universal Metal Joints, 1.0" 2-56 Standoffs, and Hardware
Assembled Chassis with Reflectance Sensor Array
Upper Chassis, SJ One Board (LPC1758), 1.25" 4-40 Standoffs, 0.75" 4-40 Standoffs, 0.375" 6-32 Standoffs, and Hardware
Assembled Upper Chassis with SJ One Board (LPC1758)
Modified USB Mini-B Cable
Assembled Chassis and Upper Chassis with Modified USB Mini-B Cable)
Line Following Robot

Hardware Interface

In this section, you can describe how your hardware communicates, such as which BUSes used. You can discuss your driver implementation here, such that the Software Design section is isolated to talk about high level workings rather than inner working of your project.

Software Design

Show your software design. For example, if you are designing an MP3 Player, show the tasks that you are using, and what they are doing at a high level. Do not show the details of the code. For example, do not show exact code, but you may show psuedocode and fragments of code. Keep in mind that you are showing DESIGN of your software, not the inner workings of it.

Software Flow Diagram for Reflectance Sensor Array Initialization
Software Flow Diagram for Reflectance Sensor Array Read
Software Flow Diagram for Dual Serial Motor Controller Initialization
Software Flow Diagram for Dual Serial Motor Controller Transmit Byte
Software Flow Diagram for Dual Serial Motor Controller Transmit Command
Software Flow Diagram for Dual Serial Motor Controller Stop Command
Software Flow Diagram for Dual Serial Motor Controller Move Forward Command
Software Flow Diagram for Dual Serial Motor Controller Turn Forward Left Command
Software Flow Diagram for Dual Serial Motor Controller Turn Forward Right Command
Software Flow Diagram for Initialization of SJ One Board General Purpose LEDs
Software Flow Diagram for SJ One Board General Purpose LED Set Control
Software Flow Diagram for Display of Reflectance Sensor Array Data on the SJ One Board General Purpose LEDs

Implementation

This section includes implementation, but again, not the details, just the high level. For example, you can list the steps it takes to communicate over a sensor, or the steps needed to write a page of memory onto SPI Flash. You can include sub-sections for each of your component implementation.

Testing & Technical Challenges

Describe the challenges of your project. What advise would you give yourself or someone else if your project can be started from scratch again? Make a smooth transition to testing section and described what it took to test your project.

Debug of the IR LED Reflectance Sensor Array and Dual Serial Motor Controller Drivers with the SJ One Board (LPC1758)

Include sub-sections that list out a problem and solution, such as:

Wifi Connection Issues

Many wifi connection issues were encountered. To solve this problem, a dedicated task was created to re-connect to wifi if the connection was ever lost.

Conclusion

Conclude your project here. You can recap your testing and problems. You should address the "so what" part here to indicate what you ultimately learnt from this project. How has this project increased your knowledge?

Project Video

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Project Source Code

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References

Acknowledgement

Any acknowledgement that you may wish to provide can be included here.

References Used

List any references used in project.

QTR-8A and QTR-8RC Reflectance Sensor Array User’s Guide

Low-voltage Dual Serial Motor Controller User’s Guide

Pololu 5V, 600mA Step-Down Voltage Regulator D24V6F5 Description

Pololu 3.3V, 600mA Step-Down Voltage Regulator D24V6F3 Description

Pololu Round Robot Chassis RRC01A User’s Guide

Video Tutorial for Crimping PCB Interconnect Cables

Appendix

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