Difference between revisions of "555 Timers"

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The 8-pin 555 timer is one of the most useful Integrated Circuits (ICs) ever made and it is used in many circuits. It is also one of the cheapest and most-rugged chips on the market costing anywhere from $0.20 to $1.20 depending on the quantity and distributor  
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The 8-pin 555 timer is one of the most popular [[Integrated Circuits]] (ICs) ever made.
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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.
  
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With just a few external components it takes about 10mA (even when the output is not driving a load) and will operate from 4v to about 16-18v which can be used to build many circuits, not all of them involve timing! A popular version is the NE555 and this is suitable in most cases where a '555 timer' is specified. You may have heard of a 556 timer also, this is simply a dual version of the 555. The dual version (556) is housed in a 14-pin package, the two timers (A and B) share the same power supply pins.  
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The 555 timer will operate from a power supply of 4 V (some versions even less) to about 16 V.
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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.
  
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The 555 relies on both analogue and digital electronic techniques to perform its functions, but if we consider its output only, it can be thought of as a digital device. The output can be in one of two states at any time, the first state is the 'low' state, which is the voltage 0V at the '-' (black) connection of your power supply. The second state is the 'high' state, which is the voltage Vs at the '+' (red) connection of your power supply. Vs is commonly 5V when using digital ICs. For convenience, these states are sometimes referred to by other names:
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Most 555 timers are connected to a couple of resistors and capacitors in one of these 4 configurations:
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* Astable - producing a square wave
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* Monostable - producing a single pulse when triggered
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* Bistable - a simple memory which can be set and reset
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* Buffer - an inverting buffer (Schmitt trigger)  
  
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Low is also known as 'space', or 'logic 0'. If a digital device is said to be 'off', its output is normally 0V.
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For more details on variety of circuits that can be built using a 555 timer, see
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High is also known as 'mark', or 'logic 1'. If a digital device is said to be 'on', its output is normally Vs.  
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* http://www.555-timer-circuits.com/
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* http://en.wikipedia.org/wiki/555_timer_IC
  
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The most common types of outputs can be categorized by the following (their names give you a clue as to their functions):  
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[[Category:Components]]
  
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Astable - producing a square wave
 
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Monostable - producing a single pulse when triggered
 
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Bistable - a simple memory which can be set and reset
 
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Buffer - an inverting buffer (Schmitt trigger)
 
  
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Original source from [http://www.555-timer-circuits.com/ 555-timer-circuits.com].
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== Example ==
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555 timer is an analog integrated circuit based on voltage comparison. If on '''pin 2''' there is a voltage which is lower than 1/3 power supply, the output ('''pin 3''') takes the high level. The circuit keeps that condition until the voltage on '''pin 6''' goes over 2/3 power supply.
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'''Pin 7''' is an electronic switch, and we use it on delay applications, to discharge the capacitor.  When the output takes the low level, pin 7 closes to the ground.
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In the following diagram you can see a possible application, based on 555.
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This simple circuit can be utilized to drive a monostable relay, using a single button switch.
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When I press the button IC output (pin3) assumes the high level, but Q1 transistor swithces
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off. So when I release it the relay is energized (now the exchange switch is closed on 5 and 9).
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When I press the button again IC output assumes the low level, but Q3 transistor switches
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on: when I release the button the circuit goes to the start condition.
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*[http://docs.google.com/leaf?id=0B7LPpongh6DzOTZlNjc3MDUtMzYwMy00ODQ2LWFmODItYmJiZTUyN2IzZDRj&hl=it Schematic]
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*[http://sites.google.com/site/plcandcircuitdiagram/home Related resources]
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*[http://www.mykoncept.com Related resources]

Latest revision as of 06:23, 23 February 2010

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


Example[edit]

555 timer is an analog integrated circuit based on voltage comparison. If on pin 2 there is a voltage which is lower than 1/3 power supply, the output (pin 3) takes the high level. The circuit keeps that condition until the voltage on pin 6 goes over 2/3 power supply. Pin 7 is an electronic switch, and we use it on delay applications, to discharge the capacitor. When the output takes the low level, pin 7 closes to the ground. In the following diagram you can see a possible application, based on 555. This simple circuit can be utilized to drive a monostable relay, using a single button switch. When I press the button IC output (pin3) assumes the high level, but Q1 transistor swithces off. So when I release it the relay is energized (now the exchange switch is closed on 5 and 9). 

When I press the button again IC output assumes the low level, but Q3 transistor switches

on: when I release the button the circuit goes to the start condition.

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