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.


  • 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 serial vs. connected in parallel
  • What voltage decay is, and how it’s used in a resistor-capacitor circuit


  • 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
  • How to use the Arduino’s constrain function to set upper and lower limits for a variable value

Robotics Skills

  • Using a pair of phototransistors for autonomous sensor navigation in response to light level

Engineering Skills

  • Subsystem testing of circuits and code routines
  • The concept of resolution, in the context of the Arduino reporting a 10-bit value from an analog input
  • Using an equation to get a zero-justified normalized differential measurement