Page 68 - 15 Dangerously Mad Projects for the Evil Genius

Chapter 4 ■ Mini Laser Turret 47

Figure 4-21 Servo motors

The 555 and 556 Timer ICs

To generate the pulses for our servo, we use a
timer chip. Actually, the chip contains two timers
in one package. That is, one for each servo.
The chip is an NE556, which contains the
equivalent of two NE555 chips, one of the best-
selling chips ever created. This chip has been
around since 1971 and sells around a billion units
a year. It can be used as both a one-shot
monostable that produces just a single pulse, or as
an astable oscillator that produces a stream of
pulses.
We use it in this astable mode. The overall
frequency and duration of the pulses are controlled
by the timing components, comprised of a
capacitor and two resistors. Figure 4-22 shows the
basic arrangement on which our design is based.
Using this arrangement, as we said before, the
circuit will oscillate, producing a waveform similar
Figure 4-22 The basic 555 timer schematic
to that shown in Figure 4-23.