Note: The circuit as shown will NOT work. You have two active TTL outputs tied together in one spot and you cannot do this. Fix that by putting in an OR or whatever gate you need. Not knowing the desired output I can't advise any further.
Some hints.
1. me, I'd simplify this. Put pullup resistors (5k, 10k, somewhere around there) on each of the 4 inputs. Then you need only SPST switches to switch the inputs to ground.
2. right now, you need 3 14 pin ICs. You could reduce this to 2 packages. The LS32 can be replaced by the unused LS08 and 3 LS04 sections.
3., redraw it to show the IC pins. Include power and ground pins.
4. redraw using the IC layout drawings for the ICs. that is, draw the 14 pin DIP outlines with pin numbers, and draw the connections between the pins.
5. From #4, it's easy to assemble the circuit.
I did not examine your schematic very closely but here are a few tips to using the solderless breadboard:
*****Before you start breadboarding, go through this tutorial:
http://www.wisc-online.com/Objects/ViewO...
Take note that not all breadboards are exactly like this so make sure you understand how yours works.
WISC-ONLINE has many more useful tutorials including a number on digital logic.
1) Start breadboarding with simple circuits. This means literally starting with something like a 9 V battery and a current limiting resistor in series with an LED. Did you calculate the proper value of the resistor so that the LED lights up but does not burn out? A typical forward voltage for an LED is somewhere in the range of 1.7 V to 2 V. That means the remaining voltage drop across the current limiting resistor is around 7 V. The LED will have a maximum current it will pass before burning out. Make your resistor large enough so that it does not allow more than that current. Then add another resistor in series so you have a voltage divider among the resistors. Measure the voltage drop across both resistors and the LED. Is is what you expected?
2) The magazine Nuts And Volts has a section for beginners.
3) Instructables is a good website to use for beginner's electronics.
4) You can check websites like Wikipedia for a list of logic ICs.
5) Use your materials provided to you in class including the textbook if you have one. A good reading of the material and working through the examples provided while covering the material can really help.
By the way, Instructables is a very good website for providing pictures of circuits that people have worked on so take advantage of that.
When you get to working with digital logic ICs make sure you take the time to figure out what the outputs are possible given all the possible inputs. This is very easy to do with a digital multimeter (or a logic tester if you have one). A logic 1 is 5 V and a logic 0 is 0 V. This is true for TTL but CMOS values are 3.3 V for a logic 1 and 0 V for a logic 0. Alternate names for 1 and 0 are HIGH and LOW. Use your truth tables to proceed through the inputs to get your outputs.
When you go to write your practical exam in this course this process will pay off. You cannot get by without putting in the time. If you put in the time, at the end of the course you will wonder what the big deal was.
OK, so let's say you do not have a digital multimeter or a logic tester. Simply use a an LED in series with a 470 ohm resistor. When the LED lights you have a logic 1. If the LED does not light or is very dim then you should have a logic 0. These calculations are not concrete but should be close. The point is you need a certain amount of current running through your circuit to light the LED as well as a certain forward voltage. These numbers can be found on your spec sheets.
The U1A/U7A issue apart there's only going to be two outputs from this circuit, zero or +5V. It doesn't matter which switches are at zero or +5V on the input the output hasn't got a clue as to which is which. As to where the 2.5V comes from is anybody's guess. It needs a serious re-think about what the circuit is supposed to do and redesign before you breadboard this. Soz mate but this is a mess at the moment.
You better go back to the drawing board, the output of the U7A 74LS04 inverter is tied to the output of the U1A 74LS08 AND gate. Neither of these TTL logic devices are tri- state or wire OR logic. If one device attemps to go to logic 1 while the other is at logic 0 the output will be undefined, the gate trying to go to logic 1 will be sourcing excessive current.
Furthermore you can probably reduce the kinds of gates used with both negative logic and the use of NAND and/or NOR gates
I really need help bread boarding this circuit. If anyone is familiar with Project lead the way, this should look familiar. This is for my digital electronics class. If anyone who is experienced with bread boarding., and they don't mind taking the time to bread board it themselves and taking reference photos would be appreciated. I'll be at work today, but I'll check this when I get home.
Best Answer will be rewarded 10 points.
Here is a picture of the circuit from Multisim: http://tinypic.com/r/20hpqbc/6
