1bit half adder with one relay

With just one double relay, you can make an adder capable of performing 1bit additions:

0 + 0 = 0
0 + 1 = 1
1 + 0 = 1
1 + 1 = 0 ( with Carry = 1 )


The circuit design isn’t mine, I found it with a quick google search.



This is the complete schematic of the above circuit.


  1. written by: model k on April 22, 2014 at 1:29 am - Reply

    i don’t understand

  2. written by: model k on April 22, 2014 at 1:38 am - Reply

    that schematic is not clear to me i have a short of seven years of studying electronics as an hobby and i can’t get what is drawn

    • written by: Mihai on April 22, 2014 at 9:39 pm - Reply

      That is a double relay, A and B are inputs ( and as it is shown in the truth table, A and B can only have two values, “1” (V+) or “0” (GND), this is done by switches ), SUM and CARRY are outputs, therefore connected to some indicators ( light bulbs, LED, voltmeters, etc).
      V+ is the operating voltage of the relay used.

  3. written by: Bilal on May 28, 2014 at 10:07 pm - Reply

    I wonder if you could make a detailed schematics for your design , I have been trying to make my own copy but I could not manage to work B input , except that all functions are working.

  4. written by: akismet on June 28, 2021 at 6:17 am - Reply

    what about full adder?

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