Page 88 - Robots Androids and Animatrons : 12 Incredible Projects You Can Build

clock pulses to a stepper motor controller chip like the UCN5804.
As the light increases, the stepper motor turns faster.
Photovoltaic
Solar cells, photodiodes, and phototransistors are similar in con-
struction. They all have a light-sensitive PN junction. Solar cells use
a wide-area PN junction to produce electric power in proportion to
light intensity.

Photodiodes are usually reverse-biased in a circuit. When light
strikes the diode’s PN junction, the current flows. The photodiode
has a quicker response than the CdS cells and can relay information
encoded in the light.
Phototransistors are light-sensitive transistors. The advantage of
a phototransistor over the photodiode is that it can provide ampli-
fication of the light signal.
Infrared

Infrared (IR) sensors detect low-frequency [900-nanometer (nm)
and longer] light. They deserve special consideration because they
are widely used in robotics for tracking, collision avoidance, and
communication. 67

Using infrared sensors has never been easier. Infrared receiver
modules that incorporate modulation detection, shown in Fig. 5.9,
are available through a number of electronic distributors. The

5.9 Infrared receiver module
Team LRN Sensors