Oh No...Ran out of PIN's.. NOR saves the day!

Discussion in 'FAQs' started by kf4jqd, Nov 22, 2006.

  1. kf4jqd

    kf4jqd Active Member

    Oh no I ran out of PIN's on my 25 PIN connector by add switching LED's! I was going to run 12vdc up the cable to the box from the Atlas Relays to indicate which way the track is switch. I have enough PIN's to do that, but I have no PIN for a common ground. :curse:

    I started to think, TTL or transitor-transitor-Logic. I thought about the NAND and NOR gates. The NOR gate will do the trick! I will tire 2 of them together. Take alook at fig 1. When S goes hi (connected to +5vdc) Q goes Hi. Even when S goes Low, Q will stay on until R is Hi. Then Q overline goes Hi.

    What does this mean? I am using mometary DPDT switches. One side is connected to the track. The over side will be connect to the NOR chip. When the switch is not in use. It is in the LOW state. Which means the track was just switch, that LED will remain lite. Until it is switched the other way. As you can see. It will take 2 NOR gates for every switch. I need a total of 2 chips for 4 switched. Only other componets I need is a 7805 voltage regulator.

    Radio Shack really makes me mad. :curse: :curse: They used to sell this componet. They don't any more!:curse: :curse: :curse: :curse: :curse: I actually found them on EBay for $.05 each!:thumb: :D Shipping cost more than what I spent!:rolleyes:

    Fig 2 is the componet layout. It is very easy to use. Plus they use low voltages. Another plus. I'll have picture of it when it's built.:thumb:


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