1

ME456: Mechatronics Systems Design

Robotics with The BOEbot v 2.2Chapter 7:

Navigating with Infrared Headlights

Prof. Clark J. RadcliffeMechanical Engineering

Michigan State University

http://www.egr.msu.edu/classes/me456/radcliff

Activity Summary

1. Building and Testing the IR Pairs.2. Field Testing for Object Detection.3. Infrared Detection Range Adjustments.4. Object Detection and Avoidance5. High Performance Navigation6. The Drop-off Detector

The Infrared (IR) Detector

• Used for digital communication– You have one in your TV set– Signals sent by an ir LED in your remote

• We will “bounce” signals– test for reflection

Infrared LED

Infrared Detector

The IR LED

• Yours is has a cover• You need to assemble it• Watch out – do not twist wires !!!

The IR LED will snapinto the shield assembly

The IR Detector

• IR Radiation is Heat radiation• Everything is hot

– You are a DC source (a big one)– Lights are an AC Source– 60 cycle power:

Filaments heat/cool 120 times/second• So how does your TV “see”

just your remote ????

The IR Detector• Your IR LED can change very fast• Your TV remote uses 38.5 kHz

– Very different far from DC (0 Hz)– Very different far from DC Lights

(120 Hz)– In fact, (f0/f) = 38.5 kHz / 120 Hz = 320

• 1st order filter reduces noise by f/f0– (120 Hz / 38.5 kHz) = 0.003 = 0.3% (20 dB/decade)

• 2nd Order filter reduces noise by (f/f0)2

– (120 Hz / 38.5 kHz) 2 = 10-5 (40 dB/decade)

2

BoE Connections

It’s crowded…Be neat and use shorter wires!!!

BoE Connections

• I changed connections to prevent shortsXP2

XP7 These changes

prevent crossedwires

XP1

The FREQOUT Trick

• FREQOUT Pin, Duration, Freq1– Designed to produce audio tones– “Aliasing” produces a 2nd “harmonic” tone

centered about 32678 Hz

“Harmonic” is low for high input frequencies:harmonic frequency = 65536 – Freq1, Freq1 ≥ 32678

“Harmonic “is high for low input frequencies:harmonic frequency = 65536 – Freq1, Freq1 ≤ 32678

Testing Your Detector

• Use Code in text BUT change pins• Avoid Shorts – No Crossed Resistors'Symbol DefinitionSpeaker PIN 4 'Piezospeaker pin (Output)LeftDetector PIN 9 'Left IR Detector Pin (input)LeftirLED PIN 8 'Left IR LED drive (output)LeftLED PIN 7 'Left Indicator LED (output)LeftServo PIN 13RightDetector PIN 0 'Right IR Detector Pin (input)RightirLED PIN 1 'Right IR LED drive (output)RightLED PIN 2 'Right Indicator LED (output)RightServo PIN 12

Orient your LEDs and Detectors

• Point them out to Left and Right

Left

Center

Right

Easy to Change Symbols

Pins defined by symbolsallow you to use symbols in your code directly

' Robotics with the Boe-Bot - TestIrPair.bs2' Test IR object detection circuits

' {$STAMP BS2}

' {$PBASIC 2.5}

'Symbols

LeftDetector PIN 9 'Left IR Detector Pin (input)LeftirLED PIN 8 'Left IR LED drive (output)

LeftLED PIN 7 'Left Indicator LED (output)

RightDetector PIN 0 'Right IR Detector Pin (input)RightirLED PIN 1 'Right IR LED drive (output)

RightLED PIN 2 'Right Indicator LED (output

3

The TestIrPair Program'VariablesirLeftSense VAR BitirRightSense VAR Bit

'Declarations INPUT LeftDetector OUTPUT LeftirLED OUTPUT LeftLED INPUT RightDetector OUTPUT RightirLED OUTPUT RightLED

The Main Program Loop

DO FREQOUT LeftirLED, 1, 38500 irLeftSense = LeftDetector FREQOUT RightirLED, 1, 38500 irRightSense = RightDetector

DEBUG HOME, "irLeftSense = ", BIN1 irLeftSense LeftLED=~irLeftSense DEBUG CR, "irRightSense = ", BIN1 irRightSense RightLED=~irRightSense

PAUSE 100LOOP