555 Timers

The 8-pin 555 timer is one of the most popular Integrated Circuits (ICs) ever made. It is also one of the cheapest chips on the market, costing anywhere from $0.20 to $1.20 depending on the quantity and distributor.

The 555 timer will operate from a power supply of 4 V (some versions even less) to about 16 V. The 14-pin 556 timer contains two 555 timers in a single package -- the two timers (A and B) share the same power supply pins.

Most 555 timers are connected to a couple of resistors and capacitors in one of these 4 configurations:

• Astable - producing a square wave
• Monostable - producing a single pulse when triggered
• Bistable - a simple memory which can be set and reset
• Buffer - an inverting buffer (Schmitt trigger)

For more details on variety of circuits that can be built using a 555 timer, see

• http://www.555-timer-circuits.com/
• http://en.wikipedia.org/wiki/555_timer_IC