Today’s Agenda

1. Scribbler Program Assignment1. Project idea due next class

2. Program demonstration due Wednesday, June 3

2. Attendance & lab pair groupings

3. Robots– Sensors– Input / Output

4. Lab 10 with Scribbler Robot

Dead Reckoning

isHARD

Move Forward indefinitelyPause for 5 secondsStop

Move Forward for 5 secondsPause for 0.2 seconds

Urban ChallengeSensors

GPSCamerasRadarLiDar

Light Detection and Ranging

OdometerGyroscope

Scribbler Sensors

1. Obstacle sensor2. Stall sensor3. Light sensors4. Line sensors

• Flashes the right infrared (IR) emitter– If the center IR detector sees the IR light

reflected back, it reports an object on the right

• Flashes the left IR emitter• If the center IR detector sees the IR light

reflected back, it reports an object on the left

Obstacle Sensor

Scribbler’sHeadlights

If obstacle on left

turn right

Else

If obstacle on right

turn left

Else

go straight

Obstacle Sensor Tips

• Infrared light reflects best off of shiny, light-colored surfaces; it is absorbed by dull, dark colored surfaces

• The Obstacle sensors work best at detecting objects 3” to 8” away

• Obstacle sensors are far from perfect, have a backup plan in case of collision– Obstacle sensors do not work at very close

range (distances of 2 inches or less)

Stall SensorThe Scribbler’s

stall sensor can tell when the motors are running but the wheels are not turning freely 0 or 1(i.e. the Scribbler is stuck)

Go Forward until Stuck!

Move Forward indefinitely

Do While <Motor Not Stalled>{

Pause 0.2 seconds // Moving Forward

}Stop

END Program

Go Forward until Stuck!

Move Forward indefinitely

Do forever If <Motor Stalled> Then Stop End Program Else Pause 0.2 seconds // Moving

Forward

Stall Sensor Tips

• The Stall sensor detects if the robots has bumped against something– Navigation by bumping into things.

This is similar to a person entering a dark room and then trying to feel their way by touching or bumping slowly into things.

• The Stall sensor is Binary: there is no way to tell if the bump was on the left or right

Stall Sensor Tips #2

• The motor must be running for Scribbler to stall– Use Move Forward indefinitely– Move Forward for 1 second will not work

• Every time you issue a Move instruction, the Stall sensor resets itself– For best results, insert a short pause

after every Move instruction before checking the Stall sensor

• The Scribbler has three photoresistor light sensors on front of the robot– The center sensor looks straight ahead– The other two sensors look 30 degrees to each

side.

• Their positioning allows Scribbler to use its photoresistors to navigate towards or away from light

Light Sensors

Do forever

Pause for 0.2 seconds

If <Light from Ahead> Then Move Forward for 1 second Else If <Light from Left> Then Turn Left for 1 second

Else If <Light from Right> Then Turn Right for 1 second

Else // no light – do nothingEND

Follow theLight

Light Sensor Tips

• There appears to be a lot of leakage of light into the Scribbler robot– Use SCP’s Sensor Monitor to get a

feeling for Scribbler’s light sensor readings

• You can cover Scribbler completely with its white box to block out all light– The sensors should read near zero

• On the bottom of Scribbler are – two Infrared

Emitters and

– two Infrared Detectors

• These allow Scribbler to see a dark line on a light background

Line Sensors

Move Forward indefinitely

Do forever

If <Line on Either Side> Then

Stop

End Program

END

Line Sensor Tips

• Line sensors are binary sensors: – 0 is white– 1 is black– Other colors are detected

as either white or black

• For best results, Use white paper with thick black lines (at least one inch)

• Line sensors are precisely positioned and work best on a smooth, hard, flat surface

Scribbler I/O

Input• Sensors

– Infrared obstacle sensor– Stall sensor– Three photoresistor

light sensors– Two infrared Line

sensors• Red reset button

Output• Motors &Wheels• Three LED’s• Speaker

Button Press

If <Button Pressed exactly 3 times> ThenLED: OFF, ON, ON

ElseIf <Button Pressed exactly 4 times> Then

LED: OFF, ON, OFFElse

If <Button Pressed exactly 7 times> Then

LED: ON, ON, ON