555 Timer - Revision history

129.105.90.217: /* Basic Operation */

2006-08-05T00:23:08Z

Basic Operation

2006-08-05T00:17:32Z

Basic Operation

2006-08-04T23:55:12Z

2006-07-11T18:46:30Z

2006-07-11T18:46:04Z

2006-07-05T16:12:14Z

2006-07-05T16:11:39Z

References

2006-07-05T16:10:04Z

References

2006-07-05T16:09:43Z

2006-07-05T14:37:01Z

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 The output of a 555 timer is either ''high'' (close to +V<sub>CC</sub>) or ''low'' (close to GND).
-Inside the 555 timer is a voltage divider the divides +V<sub>CC</sub> into thirds.  A voltage comparator compares the '''trigger''' input (pin 2) with 1/3 V<sub>CC</sub>, and another comparator compares the '''threshold''' (pin 6) with 2/3 V<sub>CC</sub>.  The point at 2/3 V<sub>CC</sub> on the voltage divider is connected to the '''control voltage''' (pin 5).  This pin can be used to modify the values of 1/3 V<sub>CC</sub> and 2/3 V<sub>CC</sub> without having to change V<sub>CC</sub>.  However, if this input is not going to be used, it should be connected to a bypass capacitor (0.01uF) to protect it from noise.
+Inside the 555 timer is a voltage divider the divides +V<sub>CC</sub> into thirds.  A voltage comparator compares the '''trigger''' input (pin 2) with 1/3 V<sub>CC</sub>, and another comparator compares the '''threshold''' (pin 6) with 2/3 V<sub>CC</sub>.  The point at 2/3 V<sub>CC</sub> on the voltage divider is connected to the '''control voltage''' (pin 5).  This pin can be used to modify the values of 1/3 V<sub>CC</sub> and 2/3 V<sub>CC</sub> without having to change V<sub>CC</sub>.  However, if this input is not going to be used, it should be grounded through a bypass capacitor (0.01uF) to protect it from noise.
 The 555 timer also has a flip-flop, which is controlled by the two comparators and the '''reset''' input.

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 The 555 timer also has a flip-flop, which is controlled by the two comparators and the '''reset''' input.
-The '''trigger''' and '''reset''' inputs are level-sensitive [[Digital#Active_Low_Input|active low]] inputs.  To activate the trigger, the voltage on the ''trigger'' pin must be pulled down to under 1/3 V<sub>CC</sub>.  The trigger experiences a delay when it "turns off," so it should be returned to ''high'' at least 10&mu;s before the end of the timing cycle to avoid double triggering.
+The '''trigger''' and '''reset''' inputs are level-sensitive [[Digital#Active_Low_Input|active low]] inputs.  To activate the trigger, the voltage on the ''trigger'' pin must be pulled down to under 1/3 V<sub>CC</sub>.  The trigger experiences a delay when changing states so it should be returned to ''high'' at least 10&mu;s before the end of the timing cycle or else the cycle will be immediately re-triggered.
 To reset the timer, the voltage on the ''reset'' pin must be pulled under 0.4V.  The ''reset'' input will override other inputs and set the '''output''' (pin 3) to ''low''.  If the ''reset'' input is not going to be used, it should be wired to V<sub>CC</sub> to prevent false signals.

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 __TOC__
+==Basic Operation==
 Connection diagram for the 555 IC timer (click for larger image).
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 The 555 timer also has a flip-flop, which is controlled by the two comparators and the '''reset''' input.
-The '''trigger''' and '''reset''' inputs are level-sensitive [[Digital#Active_Low_Input|active low]] inputs.  To activate the trigger, the voltage on the ''trigger'' pin must be pulled down to under 1/3 V<sub>CC</sub>.  The trigger experiences a delay when it "turns off," so it should be returned to ''low'' at least 10&mu;s before the end of the timing cycle to avoid double triggering.
+The '''trigger''' and '''reset''' inputs are level-sensitive [[Digital#Active_Low_Input|active low]] inputs.  To activate the trigger, the voltage on the ''trigger'' pin must be pulled down to under 1/3 V<sub>CC</sub>.  The trigger experiences a delay when it "turns off," so it should be returned to ''high'' at least 10&mu;s before the end of the timing cycle to avoid double triggering.
 To reset the timer, the voltage on the ''reset'' pin must be pulled under 0.4V.  The ''reset'' input will override other inputs and set the '''output''' (pin 3) to ''low''.  If the ''reset'' input is not going to be used, it should be wired to V<sub>CC</sub> to prevent false signals.

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 [[Image:555_symbol.png|400 px]]
-See the [[media:LM555.pdf|Datasheet for the LM555]][http://www.national.com/ds/LM/LM555.pdf Datasheet for the LM555] for more information and example applications/circuits.
+See the [[media:LM555.pdf|Datasheet for the LM555]] for more information and example applications/circuits.
 The output of a 555 timer is either ''high'' (close to +V<sub>CC</sub>) or ''low'' (close to GND).

@@ Line 4: / Line 4: @@
 [[Image:555_symbol.png|400 px]]
-See the [http://www.national.com/ds/LM/LM555.pdf Datasheet for the LM555] for more information and example applications/circuits.
+See the [[media:LM555.pdf|Datasheet for the LM555]][http://www.national.com/ds/LM/LM555.pdf Datasheet for the LM555] for more information and example applications/circuits.
 The output of a 555 timer is either ''high'' (close to +V<sub>CC</sub>) or ''low'' (close to GND).

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 ==References==
-LM555 Datasheet.
+[http://www.national.com/ds/LM/LM555.pdf LM555 Datasheet.]
 van Roon, Tony. ''555 Timer Tutorial'''. 5 July 2006. [http://www.uoguelph.ca/~antoon/gadgets/555/555.html http://www.uoguelph.ca/~antoon/gadgets/555/555.html].

← Older revision		Revision as of 16:10, 5 July 2006
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	==References==		==References==
	van Roon, Tony. ''555 Timer Tutorial'''. 5 July 2006. [http://www.uoguelph.ca/~antoon/gadgets/555/555.html].		van Roon, Tony. ''555 Timer Tutorial'''. 5 July 2006. [http://www.uoguelph.ca/~antoon/gadgets/555/555.html http://www.uoguelph.ca/~antoon/gadgets/555/555.html].

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 [[Image:555_astable_timing.gif]]
+==References==
+van Roon, Tony. ''555 Timer Tutorial'''. 5 July 2006. [http://www.uoguelph.ca/~antoon/gadgets/555/555.html].