Page 114 - Robots Androids and Animatrons : 12 Incredible Projects You Can Build

5.42 Thermistor

93

5.43 Positive (left) and negative (right) temperature co-
efficient thermistor graphs

the flexing of fingers, these versatile sensors can easily be adapted
to robotics. The bend sensor makes an interesting feeler that can
inform the robot of an obstacle.
I am reminded of a cat’s whiskers. Cats use their whiskers to deter-
mine if a particular passageway is wide enough to pass through.
If the whiskers on both sides of a cat’s face touch each side of a
passageway, the cat will most probably not try to pass through it.
The bend sensors can be used in a similar manner.

Heat
The most common heat sensor is the thermistor (see Fig. 5.42).
This passive device changes resistance in proportion to its tem-
perature. There are positive temperature coefficient and negative
temperature coefficient thermistors (see Fig. 5.43). Thermal radia-
tion can also be detected by piezoelectric materials as discussed
earlier.

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