Datasheet

Light-Sensitive Navigation with Phototransistors • Chapter 6
Robotics with the BOE Shield-Bot • 209
Here are several more light-sensing navigation ideas for your BOE Shield-Bot that can be
made with adjustments to the
loop function:
 To make your BOE Shield-Bot follow shade instead of light, place
ndShade
= -ndShade
right before the if…else statement. Curious about how or why this
works? Check out Project 2 at the end of this chapter.
 End roaming under a bright light or in a dark cubby by detecting very bright or
very dark conditions. Add
tLeft and tRight together, and compare the result to
either a really high (dark) threshold value or a really low (bright) threshold
value.
 Make your BOE Shield-Bot function as a light compass by remaining stationary
and rotating toward bright light sources.
 Incorporate whiskers into the roaming toward light activity so that the BOE
Shield-Bot can detect and navigate around objects in its way.
Chapter 6 Summary
This chapter focused on using a pair of light sensors to detect bright light and shade for
robot navigation. Lots of interesting electronics concepts and programming techniques
come into play.
Electronics
• What a phototransistor is, and how to identify its base, emitter and collector
• What wavelengths are in the ultraviolet, visible, and infrared spectrums
• What is meant by ambient light
• What the difference is between a binary sensor and an analog sensor
• What Ohm’s Law is, and how to use it to select a resistor to adjust the
phototransistor circuit’s voltage response
• Using a phototransistor as a simple binary sensor in a voltage output circuit
• What a capacitor is, and how small capacitors for breadboard circuits are labeled
in units of picofarads
• Using a phototransistor as an analog sensor in a resistor-capacitor charge-
transfer circuit, also called a QT circuit
• What it means when components are connected in series vs. connected in parallel
• What voltage decay is, and how it’s used in a resistor-capacitor circuit
Programming
• How to use the Arduino’s analogRead function to take a voltage measurement
from an analog sensor’s output
• How a sketch can measure voltage decay time from a resistor-capacitor circuit to
take a measurement from an analog sensor