Page 81 - Robots Androids and Animatrons : 12 Incredible Projects You Can Build

to, such as light, sound, or heat. The sensors one incorporates into
a robot will depend upon its intended operating environment and
application.
Signal conditioning
When determining which sensor to use for a robot, one must de-
cide how the robot will read the sensor signal. Many sensors are
resistance-type, meaning that the sensor varies its resistance in
proportion to the energy being detected. When the sensor is
placed in a simple voltage divider network, it outputs an electrical
signal whose amplitude varies in proportion to the energy it senses.

If the robot is required to read the actual energy intensity (analog),
an analog-to-digital (A/D) converter is needed. A/D converters can
measure the electrical signal and output an equivalent binary
number.
A/D converters will require a microcontroller or digital circuit to
function properly and extrapolate the data. In many cases an A/D
converter isn’t required to read sensor signals. Instead of an A/D con-
vertor one uses a comparator.
60 As its name implies, a comparator compares two voltages. One is
a reference voltage that we, the designers, set. The other voltage
is derived from the sensor (via the voltage divider). The compara-
tor can output one of two signals: high or low. The high signal is 5
V and the low signal is 0 V.
The output signal from the comparator depends upon the magni-
tude of the two voltages on its two input lines. There are three
possible choices. The sensor signal is less than the reference volt-
age, equal to the reference voltage, or greater than the reference
voltage.

Comparator example

The best way to learn about comparators is to use one in a circuit.
The first thing you notice in Fig. 5.1 is that the comparator looks
much like an operational amplifier (op-amp). This is true; com-
parators are specialized op-amps. The comparator used in our first
example is the LM339 quad comparator. This integrated circuit
contains four comparators in a 14-pin dip package. Like op-amps
the comparator has an inverting and noninverting input. In this
particular circuit the reference voltage is placed on the inverting
input ( ).

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Chapter five