Difference between revisions of "555 Timer"
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Connection digram for the 555 IC timer. |
Connection digram for the 555 IC timer (click for larger image). |
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[[Image:555_symbol.png|400 px]] |
[[Image:555_symbol.png|400 px]] |
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[http://www.national.com/ds/LM/LM555.pdf Datasheet for the LM555] |
[http://www.national.com/ds/LM/LM555.pdf Datasheet for the LM555] |
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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'''. |
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. |
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==Monostable and Astable mode== |
==Monostable and Astable mode== |
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The 555 family of timer chips can be used in either '''monostable'' mode or '''astable''' mode. |
The 555 family of timer chips can be used in either '''monostable'' mode or '''astable''' mode. |
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Revision as of 13:46, 3 July 2006
Connection digram for the 555 IC timer (click for larger image).
Inside the 555 timer is a voltage divider the divides +VCC into thirds. A voltage comparator compares the trigger input (pin 2) with 1/3 VCC, and another comparator compares the threshold (pin 6) with 2/3 VCC. The point at 2/3 VCC on the voltage divider is connected to the control voltage (pin 5). This pin can be used to modify the values of 1/3 VCC and 2/3 VCC without having to change VCC. 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.
Monostable and Astable mode
The 555 family of timer chips can be used in either monostable mode or astable' mode.
