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Author: Shuo Wu (ece265sp26 TA)

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Use this checklist to systematically debug a breadboard digital logic circuit (gates, decoders, adders, LEDs).

Checklist

1. Make sure your logic formula is correct.
   • [ ] Is your truth table correct?
   • [ ] Do you use NAND/NOR twice but you actually only need once?
   • [ ] Do you use XOR but you actually want OR?
2. Make sure your sources are good (e.g., a, b, and c can light up the LED).
   • [ ] Make sure everything is connected well with the breadboard.
   • [ ] If not, check your LED direction.
   • [ ] If still not, check battery voltage.
   • [ ] If still not, check cables.
   • [ ] If still not, check resistors.
3. For any gate/decoder/adder you used, check your input first. Does it light up the LED correctly?
   • [ ] If not, and the input is directly from the source, do step 2.
   • [ ] If not, and the input is from another gate, do step 3 to that gate.
   • [ ] If the inputs all work well, check the output. If it does not work correctly, do step 4.
4. If the input to a gate is all good, but the output is not correct, check the following:
   • [ ] Is the gate correctly put into the breadboard (deep enough)?
   • [ ] Is VCC connected to the battery and is the ground pin connected to ground?
   • [ ] For a decoder, are E1, E2, E3 connected to 0, 0, 1?
   • [ ] For an adder, is Cin connected to 0?
   • [ ] If all the above are checked and the output of the gate:
     • [ ] Is always 1: Does the cable connecting the gate and ground work well?
     • [ ] Is always 0: Does the cable connecting the gate and the battery work well?
     • [ ] If the above are checked:
       • [ ] Are any two inputs connected to the same pin of the gate and resulting in a problem?
       • [ ] Are pull-down resistors connected correctly?
       • [ ] If all the above do not work, try changing the gate

Requirements

1. Build the circuit step by step from 1 to 4. Check every input/output, and make sure they work well.
   1. For the output of the decoder, take M5 as an example: the LED connected to it should only be off when the input of the decoder is {1 0 1}.
2. If you have built the circuit and cannot find the problem, follow the steps in the order 1, 3, 4, 2.
   1. TA should know your exact problem like the following:
   2. Examples:
      1. A gate does not work (all inputs to the gate are checked).
      2. Sources (a, b, c) do not work, and the batteries have the correct voltage (all cables and resistors checked).
      3. Is my logic formula correct?