555 Timer Monostable Circuit Calculator
Input
Output
Theory of Operation
The 555 timer in monostable mode is a one-shot timer that produces a single output pulse of a specific duration when triggered. The duration of this pulse is determined by the external resistor (R) and capacitor (C) connected to the circuit.
When a trigger pulse is applied to the timer’s input (pin 2), the output (pin 3) goes high for a time duration (T), calculated as:
Pulse Width (T): T = 1.1 × R × C
- R: External resistor connected between pin 7 and Vcc (in Ohms).
- C: External capacitor connected between pin 6 and ground (in Farads).
- 1.1: A constant derived from the internal circuitry of the 555 timer.
Once the time duration T elapses, the output returns to a low state until another trigger pulse is received.
Applications
- Pulse Generators: Used to produce precise time delays for triggering other circuits.
- Timer Circuits: Useful in timing applications such as LED blinkers or power delay circuits.
- Frequency to Voltage Converters: Converts pulse durations into proportional voltage levels.
Example Calculations
Example 1: Basic Calculation
Given:
- Resistor R = 10kΩ (10,000 Ω)
- Capacitor C = 100µF (0.0001 F)
Formula: T = 1.1 × R × C
Calculation:
- Convert R and C to base units:
- R = 10,000 Ω
- C = 0.0001 F
- Substitute values into the formula:
- T = 1.1 × 10,000 × 0.0001
- Perform the multiplication:
- T = 1.1 × 1 = 1.1 seconds
Result: The output pulse width is 1.1 seconds.
Example 2: Smaller Time Duration
Given:
- Resistor R = 1kΩ (1,000 Ω)
- Capacitor C = 1µF (0.000001 F)
Calculation:
- Convert R and C to base units:
- R = 1,000 Ω
- C = 0.000001 F
- Substitute values into the formula:
- T = 1.1 × 1,000 × 0.000001
- Perform the multiplication:
- T = 0.0011 seconds or 1.1 milliseconds
Result: The output pulse width is 1.1 milliseconds.
