Electrical calculators
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Work out the frequency and duty cycle of a 555 astable, or the pulse length of a monostable.
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Frequency
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Duty cycle
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High
–
Low
–
Period
–
Worked out with
f = 1.44 ÷ ((R1 + 2·R2)·C)
Pulse length
–
One pulse each time the trigger pin is pulled low. The pulse runs its full length even if the trigger stays low for less.
Worked out with
t = 1.1 × R1 × C
Electrical calculators
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How to use it
- Pick the circuit
Astable runs free as an oscillator. Monostable gives one pulse each time it is triggered.
- Type the parts
R1, R2 and the timing capacitor, each in the unit you pick.
- Read the timing
Frequency, duty cycle, high and low times, or the pulse length, with the wave drawn.
Tips
- Duty over 50 %
In this circuit the high time is always the longer one. Make R2 much bigger than R1 to get close to 50 %.
- Parts drift
Capacitors are often ±20 %, so measure the output and trim a resistor when timing matters.
- Keep R1 sensible
Use at least 1 kΩ for R1, so the discharge pin never shorts the supply.
In the app
Electrical calculator in Angle Meter
- 555 timer with its circuit drawn
- Air-core coils, transformers and dipoles
- Speaker boxes, sealed and ported
- RC time constants and reactance
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