The Nostalgic 555 Timer IC!

This is the 555 timer Integrated Circuit with which we used to make Code Practice Oscillators when we were short wave listeners to practise Morse Code while preparing for the Amateur License Examination. In those early days of integrated circuits, it was mind boggling to think that this tiny device incorporated the equivalent of 25 transistors, 2 diodes and 15 resistors! Remember that we were just coming out of the bulky vacuum tube era.

Reverse side of 555 IC showing the 8 pin dual-in-line package (DIP), which is common package for multiple types of devices. Some of us who were scared of soldering the IC pins directly to the printed circuit board used 8 pin sockets which were soldered to the PCB and 555 IC was just inserted into it.

Here are the internal block diagram and schematic diagram of 555 IC showing the transistors, resistors and diodes on the IC 555 chip. Colours in the block diagram corresponds to the regions in the schematic diagram with same colour.