Electronic devices are based on Logic gates. These logic gates use switches to perform a logic operation. The switches in turn are of many types and evolved continuously with time.

Back in my days, there were TVs which a kid today won’t even recognize as a TV. These TVs used switches (called vacuum tubes) which were very heavy, and so were the TVs containing them. Let’s go into some details:

Actually in TVs and other electronics we implement Logic by using different combinations of switches.

The figure above is just a rough demonstration to understand the concept.

Input 1 is coming to the Green switch and Input 2 is coming to the Orange switch. The two switches perform the logic implementation and the output is delivered accordingly. There is current in both the inputs indicated by the arrows. Now let us open and close the two switches in various combinations and check the output (This is summarized in the table below)

Note: An open switch means an open circuit and a closed switch means a closed circuit.

You just performed a simple logic operation. Using this combination of switches, the current in the output will be zero only when both the switches are open (It’s a Logic Operation). It’s that simple. These two switches (performing the logic operation) form an important device called “Logic Gate”.

Switches are of different types based on “how they are operated?” . Some switches, which you and I use everyday to turn the lights and other common household appliances on or off are manually operated by us. Some switches operate by current. When you send a current to them, they are open and when you send no current to them, they remain closed. In case of current operated switches, instead of using our hand to turn the switch on and off, we use a current.

To understand this switch consider the demonstration below.

The orange circle represents a current controlled switch. When there is a current in the Control wire, the switch becomes open and no current flows in the circuit. When there is a current in the control wire, the switch is closed.

How such a switch works? What makes the switch closed when there is no current in the control wire? All these questions will be answered in the next part (Logic Gates - Part 2) .