I've had a look around at all the various different ways to build a Full Adder and decided to have a crack at it myself. I looked at what it consisted of (2 XOR gates and a few AND gates) and built a model from diagrams of the gates that I managed to find. After having built this model I tested it and funnily enough it doesn't work.

Now, I can't see where I went wrong in this as according to my logic it should work perfectly. The only thing that I see that could be happening is that there is a leakage from the base to the emitter of all my AND gates.

This is the diagram of what I've built:

enter image description here I've used 2N3904, which are BJT NPN transistors. I'm not using a ACS713 on the real thing but that was the only image that I could find that was close to what I wanted. The input voltage is 5V with a 1k Ohm resistor.

Can someone please help me to figure out what is wrong with this model and potentially give me some improvements?

Thanks in advance.

  • \$\begingroup\$ How does it fail? Is any sub-part working? \$\endgroup\$ Commented May 24, 2017 at 17:35
  • \$\begingroup\$ See: electronics.stackexchange.com/questions/300091/… and also electronics.stackexchange.com/questions/281152/… \$\endgroup\$
    – jonk
    Commented May 24, 2017 at 17:49
  • \$\begingroup\$ Why do you think your design should work? Can you expand your question to document your design thinking, as I did in the links presented to you above? And then present what you are observing? \$\endgroup\$
    – jonk
    Commented May 24, 2017 at 18:59
  • \$\begingroup\$ I looked at how each gate is made using transistors from some random internet pages I put them all together to form what I would see as a full adder. However it doesn't seem to work and I was wondering if it was down to a design fault and that their was a certain reason as to why what I've built hasn't worked. \$\endgroup\$ Commented May 25, 2017 at 17:02


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