Page 111 - Robots Androids and Animatrons : 12 Incredible Projects You Can Build

of the transducers. Turn on the receiver and transmitter circuits
and adjust R5 on the receiver circuit so that the subminiature LED
just lights.
To test the circuit, remove the solid object from the front of the
transducers; the LED should turn off. Fine-tune the circuit by
placing the solid object 5″ to 6″ in front of the transducers and
readjust R5 until the LED just lights. Note that the receiver is angle
sensitive. If the object is held at an acute angle, the ultrasonic
sound is reflected away from the receiver. The angles become less
critical as the object gets closer to the transducers.

The circuit easily detects solid objects up to 8″ away from the
transducers. Greater distances can be detected, but as mentioned
earlier they become angle sensitive. I have the transducers set
perpendicularly. You may angle the transducers slightly to obtain
different ranging effects.
The circuit provides a transistor-transistor logic (TTL) high signal
that is indicated by the lit LED whenever the circuit detects an
obstacle 6″ away. The TTL signal may be read directly by a neural
net or microcontroller.
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Arranging the ultrasonic sensors
The obvious uses for the ultrasonic system are side (left and right),
front, and back obstacle detection. Another use that may not be as
obvious is ground detection. If the ultrasonic sensor faces forward
and is pointed downward, the sensor will read the ground in front
of the robot. If the robot approaches a cliff or stair, the normally
high signal (LED lit) goes low informing the CPU to stop.

Touch and pressure

The fidelity of the human sense of touch has not been remotely
approached in robotics. However, there are a few simple sensors
that can be used to detect touch and pressure. Touch sensors are
commonly to detect bumps in the robot’s path and to allow the robot
to avoid collisions.

More sophisticated touch and pressure sensors are used on robotic
hands and arms. The sensors allow the robotic hand to grip with
enough force to lift an object without crushing it.
A simple touch or pressure sensor can be made from electrostatic
(also called conductive) foam. This is the same foam ICs are

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Chapter five