Chalk Robot ECE 445 Spring 2013 Group 12 Neil Christanto, Enyu Luo, Leonard Lim TA: Mustafa Mukadam Monday, April 29 th

Introduction Draw picture outline on the sidewalk with a normal chalk –Preloaded BMP image is converted to vector graphics –Do the kinematics using position and velocity control –Position is determined by ultrasonic sensors

Objectives Up to 1.6m x 1.6m range of drawing Draw the outline of an image Position and direction tracking within the drawing area Separate bidirectional motor control –Forward / backward movement –Turn on the spot

Block Diagram MCU Ultrasonic Rx Position Sensing MCU H- Bridge Current Sense Motor Control Board Motor Encoder Keypad Panda Board Chalk mechanism LCD

Chalk Robot

Image Processing Overview Pandaboard running Ubuntu Image Processing done onboard User selects from pre-loaded images

Image Processing Flow

Image Processing - Example

Transmitting vectors Transmitted via UART to Motor Control Board Baudrate Pandaboard uses 1.8V logic MCB uses 3.3/5V logic

Logic Conversion 1.8V  5V logic3.3V  1.8V logic

Logic Conversion - Measurement High-low transition occurs at 0.734V Rise time less than 10ns at 150kHz input

Requirements & Verifications

Position Sensing Overview Time of flight –Reference pulse –Beacon pulse Two (x,y) coordinate –Average = position –Arctan = direction

Base Station Worst case travel time: 9.16ms Worst case reflection time: 10ms 20ms for each TX 80ms reference pulse

Base Station – TX interrupt

Ultrasonic Beacons Interrupt from Base Station – start sending pulse 2 periods of 40kHz, 20Vpp square wave PWM from the microcontroller, out of phase, output 3.3V Use 2 half h-bridge supplied at 10V

Ultrasonic Beacon Output

Receiver Module Ultrasonic receivers – 40kHz Band pass filter –2 High gain amplifiers –2 nd order Low pass filter –2 nd order High pass filter Schmitt trigger – noise immunity Zener diode – 3.3V

Band Pass Filter 2 nd order, centered at 40kHz, high gain Low noise, high slew rate op-amp Noise output is less than 125mV Weakest signal is more than 400mV

Schmitt Trigger Range = 300mV –Upper threshold = 300mV –Lower threshold = 0mV

Time-of-flight

Determining Position Side is 2.4m (1.6m x 1.6m drawing area) Real x and y = 0.4m less

Determining Direction

Requirements & Verifications

Motor Control Board Gets Vectors from Panda Board Moves Motors Feedback from encoders and Position Sensing Servo control for chalk mechanism LCD display

Schematic - Power Supply

Schematic – H-Bridge

Other Hardware Encoder interface Current Sense I2C / UART Interface LCD Buzzer LEDs

PID Velocity Control

Position Control Velocity Time

Bezier Curve

Position Sensor Data Gets X, Y, angle information Glitch/Noise rejection Expected X value of 55 Sensor values: 47,0,59,70,47,48,45,80 Valid Values: 47, 59, 47, 48, 45 Take the Median: 47

Software Tasks TasksPriorityPeriodExecution time Servo Control0 (Highest)1.5 ms3.5 µs ADC140 µs2.5 µs PID Loops320 ms12 µs Communications580ms5 µs Misc. Tasks7 (lowest)0.5 s<200ms Main Program---

Requirements & Verifications

Future Work Improved User Interface –User can draw image using an App Motor Control –Instantaneous Velocity control on both wheels for Bezier instead of sampling points –Position compensation on the fly Position Sensing –Remove synchronization signal and do a time offset estimate –Automatic calibration

Special Thanks Professor Paul S. Carney Mustafa Mukadam ECE Part Shop ECE Machine Shop MIT Lincoln Lab

Questions?