Page 332 - Robots Androids and Animatrons : 12 Incredible Projects You Can Build

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16.14 Second mechanical device “lever”

IBM interface

Computer control is easy. The computer operates an electric
three-way air valve. An inexpensive three-way electrically oper-
ated solenoid air valve is available (see Fig. 16.15). This air valve
operates at 5 volts DC (VDC) and is rated at 90 psi. This air valve
5
has quick connect and disconnect air ports. The / 32"-diameter stiff
tubing is simply inserted into the port hole, and it locks in. To dis-
connect, hold and secure the port ring with your fingers into the
5
air valve and tug the / 32"-diameter air tubing out.
To operate a single air valve, we only need one pin off the parallel
(printer) port, along with a ground (see Fig. 16.16). The output pin
is buffered with a gate off of a 4050HCT noninverting hex buffer. The
output of the hex buffer turns a TIP 120 NPN Darlington transistor
on or off. The transistor controls the current going to the air valve.
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