The current available from the parallel port of a PC is enough to activate an opto-coupler. The circuit shown here uses an opto-coupler to close a relay. The relay is capable of carrying 2 amps of current , enough to run a small DC motor.

Caution! It is possible to damage your computer doing this type of experimenting. Proceed only if you have some knowledge of electronics and an inexpensive computer - a 286 is an excellent computer for doing this type of electronic interfacing.

Parts:

• R1 - 330 ohm resistor
• D1 - 1N400 Diode (Stops current spikes from relay coil, check polarity.)
• Opto-coupler - 4N29 (Darlington output, available from Active Components)
• Relay - (Radio Shack # 275-243)
• Motor - Salvage a motor from an unused battery operated toy, model car, tape recorder, etc.

This Qbasic program allows control of the parallel port. Enter "8" to turn pin 5 on, "0" to turn pin 5 off. To learn more about Qbasic, click here - Qbasic Information

• CLS
• PRINT
• PRINT " - 8 turns pin 5 on -"
• PRINT " - 0 turns pin 5 off - "
• PRINT " Press x to exit"
• SLEEP 4
• DO
•        INPUT "ENTER NUMBER - ",n
•        OUT (888), n
• LOOP UNTIL INKEY$ = "x"

Launching Model Rockets:

This circuit can also be used to launch model rockets. All safety procedures, including manual safety switches must be incorporated into the design of a computerized rocket launch system.

Examples of Rocket Launch Programs created by Hila campers.

More information about Parallel Ports

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