555 Timer Calculator: Free Online Tool for Accurate IC Timing Configurations  Astable & Monostable Modes
The 555 Timer Calculator is a digital tool designed to calculate the timing configurations of a 555 Timer IC (Integrated Circuit) which is one of the most popular and versatile ICs used in many electronic projects. The 555 timer IC can be configured in multiple modes, with this calculator specifically supporting the Astable and Monostable modes.
The calculator assists in determining the correct resistor and capacitor values for the circuit to produce a specific output waveform in these modes. The resulting waveform will have specific periods of high and low output, frequencies, and duty cycles, all based on the inputted values of resistance and capacitance.
Parameters:
 Mode Select: Users can choose between Astable and Monostable modes.
 Astable Mode: This mode is also known as the freerunning or selftriggering mode. It oscillates automatically between high (1) and low (0) state without any external triggering. This mode is often used for devices like pulse generation, LED and lamp flashers, clocks, tone generation, etc.
 Monostable Mode: This mode, also known as oneshot mode, only goes high (1) for a period determined by the resistor and capacitor, then returns to low (0). It requires an external trigger to initiate each pulse. This mode is often used for time delay applications, pulse width modulation (PWM), touch switches, etc.
Astable mode  parameters & measurement: For the Astable mode, users input values for resistors R1 and R2 (in Ohms, Ω), and capacitor C (in Farads, F).
 R1 (Ω): The resistance of resistor R1, connected between the discharge and threshold pins of the 555 timer IC.
 R2 (Ω): The resistance of resistor R2, connected between the threshold and trigger pins of the 555 timer IC.
 C (F): The capacitance value of the capacitor connected between the trigger pin and ground in the 555 timer IC circuit.
Results:
After the user enters the required parameters, the calculator will output:
 Time High (ms): This is the duration (in milliseconds) of the output pulse when it is in the high state (1).
 Time Low (ms): This is the duration (in milliseconds) of the output pulse when it is in the low state (0).
 Cycle Duration (T) (ms): This is the total duration of one complete cycle of the output waveform (in milliseconds), the sum of time high and time low.
 Cycle Frequency (f) (Hz): This is the frequency of the output waveform (in Hertz), which is the reciprocal of the total time period T (f = 1/T).
 Duty Cycle Calculator Duty Cycle (%): The duty cycle is the percentage of one period in which a signal or system is active. In this context, it is the ratio of the Time High to the total period (T), expressed as a percentage.
The 555 Timer Calculator therefore provides a valuable tool to simplify the calculations required for setting up a 555timer circuit, allowing you to focus on the implementation and overall design of your electronic projects.
Math:
The mathematical calculations involved in the 555 Timer Calculator, specifically for the Astable mode, are based on the following equations:

Time High (ms):
The time duration for which the output pulse remains high (T_high) can be calculated using the following formula:
T_high = 0.693 * (R1 + R2) * C
This equation is derived from the charging time of a capacitor through a resistor in an RC (ResistorCapacitor) circuit.

Time Low (ms):
The time duration for which the output pulse remains low (T_low) can be calculated using the formula:
T_low = 0.693 * R2 * C
This equation is derived from the discharging time of the capacitor through R2.

Cycle Duration (T) (ms):
The total time period of one complete cycle of the output waveform (T) is the sum of T_high and T_low.
T = T_high + T_low

Cycle Frequency (f) (Hz):
The frequency of the output waveform (f) is the reciprocal of the total time period (T), and is usually represented in Hertz (Hz).
f = 1/T

Duty Cycle Calculator Duty Cycle (%):
The duty cycle (D) is the percentage of one period in which a signal or system is active. It is the ratio of the Time High to the total period (T), and it's expressed as a percentage.
D = (T_high / T) * 100%
These calculations help you understand the timing behavior of the 555 timer in Astable mode and also guide you in choosing the correct resistors and capacitors for your specific needs.
Disclaimer:
It is believed that these calculations are accurate, but not guaranteed. Use at your own risk!