The 555 timer IC is an integrated circuit (chip) used in a variety of timer, pulse generation and oscillator applications. The part is still in widespread use, thanks to its low price and ubiquity. The 556 timer is simply two 555 timers in a single package.
The 555 timer IC is a monolithic integrated-circuit (chip) used in a variety of timer, pulse generation and oscillator applications. The part is still in widespread use, thanks to its ease of use, low price and good stability. In 2017, some estimates amounted to a billion 555 timers produced annually. - Wikipedia
It can be found in a variety of versions, both cmos and ttl, metal or plastic packaging. It even comes in a dual package as the 556 Timer, providing two independently programmable 555 timers. There is a less common 558 Quad timer, but it has some pins of the 4 internal 555 timers connected together internally.
Further reading:
- NE555 datasheet, LM555 datasheet. Two versions of the same chip by different manufacturers.
- NE555 and NE556 applications, Philips (NXP) application note
555 circuit collections:
One could also call these "cookbooks".- 555 timer circuits
- 555 timer circuits (another different one)
- 555 timer by Doctronics
- Fifty 555 circuits by Colin Mitchell
