How to make a digital number detector: Circuit diagram

In the last article we learned how we can play with the equation of a logic circuit and how we can represent it by means of truth tables or chronograms. In today's article we will explain how to implement any type of equation in a circuit.

First of all, it is important to know the symbology.

Symbology logic gates

Each symbol corresponds to a logic gate that performs an operation. Its operation is as follows:




NAND: (A+B)'.

NOR: (A*B)'

XOR: A'B+AB' = A(+)B

If we substitute this symbology in our circuit number detector (from 0 to 9) we will obtain the following result:

S = (A1′*A2′)+A3′

Logic Circuit

As you can see in the design, each input is drawn only once, even if it is not going to be used, as well as the output.

In addition to these simple logic gates, there are some logic blocks that are very useful when making our circuits. These are the following:

EncoderThe input is activated, which is identified by a decimal number and displays the equivalent binary number on its output. There is also a decoder that performs the inverse function.


MultiplexerIt works like an electrical switch. It consists of a circuit that has selection inputs that inform about the input that must go to the output. Thus, if the selection inputs show the code 01, the input I1 will be sent to the output. As in the previous case, there is also a demultiplexer.


As always, remember that you can use our forum to answer any questions you may have.

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