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Thread: Logic Gate circuit

  1. #1 Logic Gate circuit 
    Forum Junior DivideByZero's Avatar
    Join Date
    Dec 2007
    Hi, I want to make a simple AND logic gate using transistors.

    I found this diagram:

    I believe it is using 2 NPN transistors to make an AND logic gate.

    I've been trying to make a simple gate with two switches but I'm failing miserably.

    The transistor I bought looks like this:

    I just can't figure out where the ground end goes and how the switches are wired to the battery. Can someone please help me out? Can someone draw out a diagram including the power source for this AND gate with the two switches and a light bulb?

    I've tried many times but can't figure out why the light bulb won't turn on when both switches are down.

    thank you so much in advance.

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  3. #2  
    Forum Freshman
    Join Date
    May 2009
    sei italiano ? io nn sn ancora arrivato a quel punto con le porte ma penso che tu mi potresti aiutare nel mio progetto light saber, no ?

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  4. #3  
    Join Date
    Apr 2007
    E, B, and C stand for emitter, base and collector. The emitter is shown on your diagram with an arrow symbol. The collector is the pin connected to the + voltage. The base has the input resistors connected to it.

    You would connect one side of each of the the two input switches to A and B. The positive terminal of your 6 volt battery would connect to the other side of the switches and to the collector of the A transistor. The negative side of the battery would connect to where the ground symbol is shown on the 4.7K resistor and to one side of the 6 volt lamp. The other side of the 6 volt lamp connects to the terminal labeled "Out" on your diagram.

    If you are still having a problem, take your voltmeter and measure the voltage to ground at each terminal of the transistors. Make a table. I'm sure somebody can help troubleshoot your circuit with that info.
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