In this page, we will introduce two examples of how logic circuits are actually used in our daily lives.

Switches that can be turned
on and off from both the first and second floors

As shown in the diagram above, there is a light near the top of the stairs,
and the light can be turned on and off freely from the switches on the first and second floors.

This can be achieved by using the XOR Circuit introduced in the Basics of Logic Circuits.
If we replace the input of the XOR circuit with a switch and the output with an electric light,
the truth table will look like the one below.

To switch switch 1

At first, we will consider fixing switch 2 to OFF and switching switch 1 ON/OFF.
From the truth table, even if switch 2 is left OFF
You can see that the lights can be turned on and off freely by switching switch 1 on and off.
This is the same when switch 2 is fixed to ON.

To switch switch 2

Next, we will consider fixing switch 1 to OFF and switching switch 2 ON/OFF.
In the same way, from the truth table, we can see that the light can be
turned on and off freely by switching switch 2 on and off, even if switch 1 remains off.
This is, of course, also true when switch 1 is fixed at ON.

Summary

From the above,we can see that the light can be turned on and off freely with one switch,
regardless of the status of the other switch.
Thus, the lights can be turned on and off freely from switches on both the first and second floors.

Bus drop-off button

In the bus, pressing any of the get off buttons will cause all the LEDs in the bus to light up.
This can also be realized by logic circuits.

The bus drop-off button is made up of several RS flip-flop circuits, as shown here.
The output from the last Q is summed up in an OR circuit, and the output is transmitted to the LED.

S and R are connected to the get off button and the light off button respectively.
When any of the yield buttons is pressed,
the ON signals output from Q are put together in an OR circuit, and the LED lights up.
Also, since it is through a flip-flop circuit,
the LED does not turn off even if the button is released The LED does not go out. .
On the other hand, when the light off button is pressed,
the signal goes to all R The output (Q) of the flip-flop circuit is turned off,
and the lamp is turned off.

Summary

As mentioned above, logic circuits are also used in various places in our daily lives,
such as the stairs in our houses and on the bus.
It is just that we don't know about them, but logic circuits are surprisingly familiar to us.