How to Implement a Full Adder Circuit Using 3 To 8 Decoder

The full adder circuit is a critical component in digital electronics. It can be used to perform addition or subtraction of two binary numbers. It is a combinational logic circuit that adds two binary numbers and provides the sum and carry output. In this article, we will discuss how to implement a full adder circuit using 3 to 8 decoders. We will cover the circuit diagram, wiring diagrams, and the working of the circuit. Additionally, we will also talk about how to test the circuit.

What is a 3 to 8 Decoder?

A 3 to 8 decoder is a combinational logic circuit used to convert a 3-bit binary number into one of eight possible output selections. It is also known as an octal decoder. It has three data inputs (A, B, C), an enable input (E), and eight outputs (Y0 – Y7). The outputs are activated when the enable input is active. The decoders are widely used in memory address decoding, interfacing, and for converting data from one form to another.

Wiring Diagrams

To implement a full adder circuit using a 3 to 8 decoder, you need the following components:

• 3 to 8 decoder


• 2 NOT gates


• 2 AND gates


• OR gate

The wiring diagram of the full adder circuit is shown in the figure below:

Working of the Circuit

The circuit consists of three data inputs (A, B, C) and two outputs (SUM, CARRY). The SUM output is the sum of the two binary inputs A and B. The CARRY output is the overflow of the sum calculation. The 3 to 8 decoder is used to decode the three input bits and generate the output. The NOT gates are used to invert the input bits. The two AND gates are used to generate the CARRY output and the OR gate is used to generate the SUM output.

The circuit works as follows:

• When the inputs A and B are 0, the output SUM will be 0 and the CARRY output will be 0.


• When A and B are 1, the output SUM will be 0 and the CARRY output will be 1.


• When A is 0 and B is 1, the output SUM will be 1 and the CARRY output will be 0.


• When A is 1 and B is 0, the output SUM will be 1 and the CARRY output will be 0.

Testing the Circuit

To test the circuit, you can use a logic probe or an oscilloscope. You can use the logic probe to check the logic levels of the inputs and outputs. You can use the oscilloscope to check the timing of the signals. This will help you determine if the circuit is working correctly.

In conclusion, this article discussed how to implement a full adder circuit using a 3 to 8 decoder. We covered the circuit diagram, wiring diagrams, and the working of the circuit. Additionally, we discussed how to test the circuit. With the help of this article, you can now design and implement your own full adder circuit.