A logic level shifter is use to shift one voltage level to another which is essential for some digital chips to work.

Let's take a example when we want to upload a sketch to the esp8266-01 by using arduino we need to shift tx logic of arduino to 3.3v. As arduino logic level is 5v, it is dangerous for esp8266. It may get damaged, so we need logic level shifter.

Let's make a simple logic level shifter using two npn transistors. These types of level shifter are widely use in many of the digital devics. In this instructables we are going to design a simple circuit of level shifter just for understanding how they works. Practically cmos are preferred for making logic level shifters.