Editing 555 timer IC (section)

=== Monostable ===
{{stack|[[File:555 Monostable.svg|thumb|Schematic of a 555 in monostable mode. Example values C = 100&nbsp;nF, R = 180&nbsp;kΩ to 220&nbsp;kΩ for debouncing a pulled-up pushbutton.]]}}
{{stack|[[File:NE555 Monotable Waveforms (English).png|thumb|Waveform in monostable mode]]}}
{{see also|RC circuit}}

Monostable mode produces an output pulse when the trigger signals drops below {{Frac|1|3}} ''V''<sub>CC</sub>. An [[RC circuit]] sets the output pulse's duration as the time <math>t</math> in [[second]]s it takes to charge C to {{Frac|2|3}} ''V''<sub>CC</sub>:<ref name="Signetics_1973_555-556_Databook" />

: <math>t = \ln(3) \cdot R \cdot C,</math>

where <math>R</math> is the resistance in [[ohm]]s, <math>C</math> is the capacitance in [[farad]]s, <math>\ln(3)</math> is the [[Natural logarithm|natural log]] of 3 constant.{{efn|[[Natural logarithm|ln(3)]] is a constant, approximately 1.098612 (rounded to 6 significant digits), or commonly rounded to fewer digits in 555 timer books and datasheets to 1.099 or 1.1}}  The output pulse duration can be lengthened or shortened as desired by adjusting the values of R and C. Subsequent triggering before the end of this timing interval won't affect the output pulse.<ref name="TI_LM555_Datasheet" />

==== Example values ====
{| class="wikitable floatright" style="text-align: right"
|-
|+ Monostable mode examples with [[E series of preferred numbers|common values]]
! [[Second|Time]] !! [[Farad|C]] !! [[Ohm|R]]
|-
| 100 μs (−0.026%) || 1 nF || 91 kΩ
|-
| 1 ms (−0.026%) || 10 nF || 91 kΩ
|-
| 10 ms (−0.026%) || 100 nF || 91 kΩ
|-
| 100 ms (−0.026%) || 1 μF || 91 kΩ
|-
| 1 s (−0.026%) || 10 μF || 91 kΩ
|-
| 10 s (−0.026%) || 100 μF || 91 kΩ
|}<!-- NOTE: Common preferred values are best for examples. Capacitors are E3 series values, resistors are E24 series values. user:sbmeirow -->

The timing table (right) shows common electronic component value solutions for various powers of 10 timings.

Scaling R and C by opposite powers of 10 will provide the same timing. For instance:<!-- NOTE: per [[Wikipedia:These are not original research#Simple calculations]], from user:sbmeirow -->
* 1{{nbsp}}ms [[≅]] 1{{nbsp}}nF and 910{{nbsp}}kΩ,
* '''1{{nbsp}}ms ≅ 10{{nbsp}}nF and 91{{nbsp}}kΩ (values from table)''',
* 1{{nbsp}}ms ≅ 100{{nbsp}}nF and 9.1{{nbsp}}kΩ.

For each row in the example table (right), additional timing values can easily be created by adding one to three of the same resistor value in parallel and/or series. A second resistor in parallel, the new timing is half the table time. A second resistor in series, the new timing is double the table time.<!-- NOTE: per [[Wikipedia:These are not original research#Simple calculations]], from user:sbmeirow -->
* 2.5{{nbsp}}ms (0.25x) [[≅]] 100{{nbsp}}nF and 22.75{{nbsp}}kΩ (four 91{{nbsp}}kΩ resistors in [[Series and parallel circuits|parallel]]),
* 5{{nbsp}}ms (0.5x)  ≅ 100{{nbsp}}nF and 45.5{{nbsp}}kΩ (two 91{{nbsp}}kΩ resistors in parallel),
* '''10{{nbsp}}ms (1x) ≅ 100{{nbsp}}nF and 91{{nbsp}}kΩ (values from table)''',
* 15{{nbsp}}ms (1.5x) ≅ 100{{nbsp}}nF and 136.5{{nbsp}}kΩ (one 91{{nbsp}}kΩ resistor in series with "two 91{{nbsp}}kΩ resistors in parallel"),
* 20{{nbsp}}ms (2x) ≅ 100{{nbsp}}nF and 182{{nbsp}}kΩ (two 91{{nbsp}}kΩ resistors in [[Series and parallel circuits|series]]),
* 25{{nbsp}}ms (2.5x) ≅ 100{{nbsp}}nF and 227.5{{nbsp}}kΩ ("two 91{{nbsp}}kΩ resistors in series" in series with "two 91{{nbsp}}kΩ resistors in parallel"),
* 30{{nbsp}}ms (3x) ≅ 100{{nbsp}}nF and 273{{nbsp}}kΩ (three 91{{nbsp}}kΩ resistors in series),
* 40{{nbsp}}ms (4x) ≅ 100{{nbsp}}nF and 364{{nbsp}}kΩ (four 91{{nbsp}}kΩ resistors in series).
{{clear}}