breadboarddigital-logiclogic-gates
I am supposed to design my first circuit on a breadboard and the output will be defined by the logical formula:
ab + a'c
The problem is I don't understand how are the inputs placed, a b c as inputs are three connections to the main power souce? or what?
I tried to test a simpler circuit:
a+b
But my simulation doesn't light the led. Can someone tell me why is this wrong?
You connected the DIP switches between Vcc and the AND gate's input, and that's wrong. A floating TTL input (DIP switches off) is seen as logical 1, and when you close the switch you just enforce that 1. So inputs are always seen a 1, and output will be 1, and the LED will light.
Two things:
Assuming the redrawn schematic is an accurate representation of what you actually built, then the problem is that you have the LED connected directly in parallel with the B-E junction of Q2.
The circuit is working, but Q2 prevents the voltage across the LED from rising high enough to light it up.
The fix would be to make the connection between the base of Q2 and the LED using another 10 kΩ resistor. This will limit the current into Q2's base and allow the LED to light up.
Best Answer
If, as you commented: "I actually designed the circuit using 1 or, not, and gates each.", then your lineup is wrong and should be:\$\ \$ two ANDs, one NOT, and one OR, and your logic should look like this:
I don't know what you're trying to imply with your breadboard example, but in the real world it should look something like this: