Using IR Chapters 7 & 8 of Robotics with the Boe-Bot

Wireless Communication Wireless communication: Personal organizers beam data into desktop computers wireless remotes let us channel surf. Many remote controls and PDA’s use signals in the infrared frequency range to communicate, below the visible light spectrum. With a few inexpensive and widely available parts, the BASIC Stamp can also receive and transmit infrared light signals

Visible Light Waves

Infrared

The IR Detector The IR detector is only looking for infrared that’s flashing on and off 38,500 times per second. It has built-in optical filters that allow very little light except the 980 nm infrared. It also has an electronic filter that only allows signals around 38.5 kHz to pass through. This prevents IR interference from common sources such as sunlight and indoor lighting.

Schematics

Testing the IR Pairs Using FREQOUT The FREQOUT command was designed mainly to synthesize audio tones. The actual range of the FREQOUT command is 1 to Hz. One interesting phenomenon of digitally synthesized tones is that they contain signals called harmonics.

Fundamental Frequency and Harmonics Unfiltered freqout pulses sent by freqout pin, period, 27036

Detecting IR The key to making each IR LED/detector pair work is to send 1 ms of 38.5 kHz FREQOUT harmonic, and then, immediately store the IR detector’s output in a variable. FREQOUT 8, 1, irDetectLeft = IN9 The IR detector’s output state when it sees no IR signal is high. When the IR detector sees the Hz harmonic reflected by an object, its output is low. The IR detector’s output only stays low for a fraction of a millisecond after the FREQOUT command is done sending the harmonic, so it’s essential to store the IR detector’s output in a variable immediately after sending the FREQOUT command.

Simple Display Program

IR Detection Range Less series resistance will make an LED glow more brightly. Brighter IR LEDs can make it possible to detect objects that are further away.

OBJECT DETECTION AND AVOIDANCE

Other Tricks Drop off detection Simulating a drop-off with electrical tape Distance detection Following a stripe Communication