Inside the 555 Timer
You may wonder what is inside the 555 timer chip or what makes it work. Well, the 555 timer chip an Intergrated Circuit (IC) and therefore it contains a miniturized circuit surrounded by silicon. Each of the pins is connected to the circuit which consists of over 20 transistors, 2 diodes and 15 resistors.
The illustration below shows the functional block diagram of the 555 timer IC.
Do you notice the three 5k resistors? This is how the chip got it's name.