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I recently got my hands on a sn74ls83an 4 bit adder adder chip.I made my own circuit and it doesn't work.Here is the circuit diagram(sorry for the messy wiring:

enter image description here

I used a 4 switch dip switch instead of the slide switches in the diagram.The exact chip name is:SN74LS83AN from texas instruments.

I am powering the circuit with a micro usb wall wart with an output of 5v at 500mA.

Here is the datasheet for the chip:http://pdf1.alldatasheet.com/datasheet-pdf/view/80346/TI/SN74LS83A.html

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  • \$\begingroup\$ Note:the top set of switches is the a input and the bottom set of switches is the b input \$\endgroup\$ – zack1544 Sep 26 '15 at 0:46
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    \$\begingroup\$ The messy wiring is enough for me to not even attempt to look at your circuit. If you want help, why not spend the time to make sure your circuit is easily readable. It would help even more, if you provided a schematic and not a fritzing wiring diagram. \$\endgroup\$ – efox29 Sep 26 '15 at 0:57
  • \$\begingroup\$ Check your bread board power rails, some need jumpers to connect left and right banks. \$\endgroup\$ – Tyler Sep 26 '15 at 1:03
  • \$\begingroup\$ sorry for the wiring efox29(I am new to fritzing)where can I make a schematic diagram?are there online tools that you can use? \$\endgroup\$ – zack1544 Sep 26 '15 at 1:31
  • \$\begingroup\$ The breadboard power rails are connected internally. I just checked the circuit. \$\endgroup\$ – zack1544 Sep 26 '15 at 1:34
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First of all, you don't say what doesn't work. Do the LED's ever light up? Under what conditions?

I checked all of the wiring, and it looks okay (with one exception, see below); this is assuming the switches are wired correctly as you didn't provide a datasheet for them.

The one wiring anomaly is that you have n input (C0) that is left unconnected; this is not a good idea with TTL (or any logic for that matter). Tie it either to ground or to VCC, and then use the left half or right half for the Outputs section of the truth table in the datasheet.

It's better actually to connect inputs like C0 to VCC through a resistor, like 4.7K. This goes for all the switch inputs also. However your circuit should work as shown with them tied to VCC.

There are some breadboards where power and ground are interrupted at the midpoint, and you need to bridge across the two sections horizontally so you have VCC and ground on both sides. If this is the case, there is usually a bigger separation between those sections than the others.

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    \$\begingroup\$ The circuit works now.I actually had Cin connected to ground(I forgot to add it to the diagram), which caused the three leftmost output bits to turn on when I powered the circuit.(I don't know why this happened)When I removed it I found out that the outputs were inverted.I don't think that the inverted outputs was mentioned in the datasheet. Now it's working.Thanks for your response! :) I am new to circuit building, and your answer has given me tips and general things I should know about TTL. \$\endgroup\$ – zack1544 Sep 26 '15 at 5:42

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