DivideByZero Posted May 26, 2009 Share Posted May 26, 2009 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. :evil: thank you so much in advance. I also found this circuit board online: In that diagram I don't know where the power source comes in. Also what connects to that node in the bottom right?? Help! Link to comment Share on other sites More sharing options...
Externet Posted May 27, 2009 Share Posted May 27, 2009 (edited) Hi. The first schematic is a theoric analogy for the AND gate. The lamp, relay or load would connect between the 'out' node and the ground (bottom) The positive of your battery goes at the top and its negative to the ground. The second schematic is very wrong. Erase the short vertical line portion above the top transistor that joins the red and black curved wires. The leftmost vertical line is very wrong. Puts a direct short circuit connection between the battery terminals. At least erase the portion from the "0V" up to the lower B switch The bulb won't shine bright as has a 680 ohm resistor in series with it. A led instead of the light bulb would work much better. Observe polarity if you replace it. Anode to the top (+) , cathode to the upper transistor collector. The top horizontal line is where you connect your 6V battery (+); the bottom horizontal line is for the battery (-) Ignore or erase the rightmost extension of the bottom line, (from the 680 ohm resistor towards the right.) Miguel Edited May 27, 2009 by Externet 1 Link to comment Share on other sites More sharing options...
DivideByZero Posted May 27, 2009 Author Share Posted May 27, 2009 Will this be guaranteed to work? Link to comment Share on other sites More sharing options...
Externet Posted May 27, 2009 Share Posted May 27, 2009 It should. Come back with results. Some transistors have the habit of staying on when a 'pull down' resistor is omitted, but go ahead. Miguel Link to comment Share on other sites More sharing options...
DivideByZero Posted May 27, 2009 Author Share Posted May 27, 2009 one more thing... Do I need any of the resistors? or can I just build it without the resistors? Link to comment Share on other sites More sharing options...
Externet Posted May 28, 2009 Share Posted May 28, 2009 You do need those two 1000 ohms resistors in the circuit. Miguel Link to comment Share on other sites More sharing options...
DivideByZero Posted May 28, 2009 Author Share Posted May 28, 2009 Oh My God it worked!!!!!!!!! Thank you so much Miguel!!!!! You're the best! +rep!! Thank you thank you thank you thank you! Link to comment Share on other sites More sharing options...
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