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I have a question that i hope that someone here can help me with. I am working through this tutorial http://www.play-hookey.com/digital/experiments/dl_or2.html on OR gate with diodes and the accompaning tutorial on AND gate the OR gate looks like this[br] dl_or2_full_sch.gif[br] I can understand what is going on here, seeing the diode direction. The AND gate looks like this [br] dl_and2_full_sch.gif[br]This one I don't understand it seems that if you just press one of the buttons that current would go through to the output. After staring at this thing for a while I realized that the diodes where going in the opposite direction from the ones in the OR gate. Could someone tell me if I am right about the diode direction and what is actually happening here. Hopefully I am making sense here, if not let me know. :)

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In the first example, you can close either switch and the other side of the circuit will continue to give you a voltage to the output. Only when both switches are closed will you get a change in state of the output. In other words, when S1 "AND" S2 are closed, the circuit will change state. This causes the circuit to act as an AND gate. Both switches must be closed to change state.

In the second example, either switch closing will cause the output to change state from high to low. Both switches do not have to be closed for this action. Closing either switch will cause a change of state. Of course, closing both switches will give the same result as closing either switch individually. This causes the action of an OR gate. Switching S1 "OR" S2 "OR" both will cause the output to change state.


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Yes, it is certainly not an OR gate or an AND gate, but I suppose that in the most simple application, you could replace the switches with digital 0 or 5V and have a simple gate. Digital gates actually have more function whereas they can buffer and improve your signal.
I did not check the link, but I think the site was a tutorial to teach how the actual gates function in simple terms.
In keeping with the same subject, here are some examples of using transistors as gates.



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