Xtreme Robot OlympiadProgramming with Sensors

Dr. Peter Laz Associate Professor

Department of EngineeringUniversity of Denver

Outline

• Microcontroller architecture• Digital versus analog signals

• Line sensors

• Ultrasonic sensors

• Programming with EasyC

Robot Control

• We programmed the vehicle to perform specific actions • Drive in a square• “dead reckoning”

• By adding sensors, we can make the vehicle “smart” by making decisions based on the readings of the sensor

Digital versus Analog

• Digital signals• Two levels: 0 or 1• Binary

• Analog signals• Infinite number of levels• Signals can be between 0 and 1000• Calibrate readings to physical meaning

Microcontroller• Ports have different types of signals

• Analog 1-4• Digital 5-10

Motors

InterruptsAnalog/Digital Signals (Sensors)

Line Sensor• Uses an Infrared (IR) LED emitter and detector

to measure intensity• LED = light emitting diode

• Distance of the sensor to surface will affect readings

Emitter Detector

Sensor

Ultrasonic Sensor

• Uses ultrasound to measure time for a pulse to bounce off of an object• Time and known speed to sound distance

• Sound waves must reflect off the object• Difficulty with curved objects

Emitter

Detector

Sensor Object

Exercises

• Download LinefollowerTest.ecp• What reading corresponds to white?• What reading corresponds to black?• Test how distance from the surface affects the

reading

• Download UltrasonicTest.ecp• How does the reading vary with distance?• How close can you get?• What reading do you get with a curved surface?

The Grand Challenge

• Two competitions• Autonomous maze

• Navigate through a maze using sensors and autonomous control

• Additional time bonus for stopping within 2” of the wall without touching it

• New adventure race with your team’s best driver

The Grand Challenge

• Teams will use the same vehicle for both competitions• Exception different programs will be downloaded

• Autonomous maze 50 pts

• Adventure race 50 pts

Line Follower Logic

Left Right Left Center Right

• Use multiple sensors together to make a “smart” line following robot

• What decisions are made based on the readings on the different sensors?

Two Sensor Configuration Three Sensor Configuration

Line Follower Logic

• If both see line • Then go _______

• If left sensor sees line• Then turn _______

• If right sensor sees line• Then turn _______

• If no sensors see line• Then _______

Left Right

Two Sensor Configuration

Line Follower Logic

• What sensor reading is on the line?• How much do you turn?• How fast can you go without losing the line?

• Develop a robust program• Consider what to do if you lose the line• Consider right angles and “T”s

• If … then … or If … then … else …

Exercises

1. Write a code to follow the line• Use the test field to test your program• Program and test

2. Develop a code to earn the stopping distance bonus

3. Make changes to your vehicle for the final mission• Again, hanging bonus is in play

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