Page 120 - Robots Androids and Animatrons : 12 Incredible Projects You Can Build

pulse generator. The output (pin 3) of the 555 remains low until a
negative pulse on the number 2 pin triggers its operation. Once
triggered, the output (pin 3) of the 555 goes high for approxi-
mately 1 s.
The output of the 555 connects to a 2N2222 NPN transistor. An
output is taken off the emitter of the transistor and connected to a
buffer on the 4049 hex inverting buffer IC. The buffers on the 4049
chip are connected to a four-MOSFET (metal oxide semiconduc-
tor field-effect transistor) H-bridge that controls the drive motor.
When the output of the 555 timer is low, the H-bridge powers the
robot’s drive motor forward. The sensor to be tested is connected
to the trigger input, pin 2 on the 555 timer. The sensor is wired in
such a way as to cause a negative pulse (goes to ground) when it is
activated or tripped. The negative pulse on pin 2 causes the output
of the timer to go high for 1 s, which reverses the motor direction
for 1 s.
Tester can be used to check a variety of sensors and transducers.

Improving the tester robot
When I designed Tester, I had imagined most of the sensors I
would test and use to be tiny miniature modules. This was not the 99
case. In the process of prototyping different circuits I rarely had
the time to produce a PCB, let alone miniaturize the circuit.

If I were to build another tester robot, I would use a much larger elec-
tric car as a foundation. Having a lot of room to work on the robot
makes it easier to secure different types of sensors and circuits.
Parts for the projects outlined in this chapter are available from:
Images Company
P.O. Box 140742
Staten Island, NY 10314
(718) 698-8305
http://www.imagesco.com

Team LRN Sensors