The Traffic Light Hack


The 74HCT125

Here is the diagram for the CMOS chip, scanned in from the packaging. Since this is a tri-state chip, and lights are only two states (on or off), the third state had to be disabled by attaching all the OE pins to ground. The 5VDC from an AC adapter comes in through the VCC pin, three pins from the parallel port are attached to 1A, 2A, and 3A, and the three relays are attached accordingly to 1Y, 2Y, and 3Y.
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May 2005  

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