ic_555_timer.py

from __future__ import annotations

"""
 Calculate the frequency and/or duty cycle of an astable 555 timer.
 * https://en.wikipedia.org/wiki/555_timer_IC#Astable

 These functions take in the value of the external resistances (in ohms)
 and capacitance (in Microfarad), and calculates the following:

 -------------------------------------
 | Freq = 1.44 /[( R1+ 2 x R2) x C1] | ... in Hz
 -------------------------------------
 where Freq is the frequency,
 R1 is the first resistance in ohms,
 R2 is the second resistance in ohms,
 C1 is the capacitance in Microfarads.

 ------------------------------------------------
 | Duty Cycle = (R1 + R2) / (R1 + 2 x R2) x 100 | ... in %
 ------------------------------------------------
 where R1 is the first resistance in ohms,
 R2 is the second resistance in ohms.
"""


def astable_frequency(
 resistance_1: float, resistance_2: float, capacitance: float
) -> float:
 """
 Usage examples:
 >>> astable_frequency(resistance_1=45, resistance_2=45, capacitance=7)
 1523.8095238095239
 >>> astable_frequency(resistance_1=356, resistance_2=234, capacitance=976)
 1.7905459175553078
 >>> astable_frequency(resistance_1=2, resistance_2=-1, capacitance=2)
 Traceback (most recent call last):
 ...
 ValueError: All values must be positive
 >>> astable_frequency(resistance_1=45, resistance_2=45, capacitance=0)
 Traceback (most recent call last):
 ...
 ValueError: All values must be positive
 """

 if resistance_1 <= 0 or resistance_2 <= 0 or capacitance <= 0:
 raise ValueError("All values must be positive")
 return (1.44 / ((resistance_1 + 2 * resistance_2) * capacitance)) * 10**6


def astable_duty_cycle(resistance_1: float, resistance_2: float) -> float:
 """
 Usage examples:
 >>> astable_duty_cycle(resistance_1=45, resistance_2=45)
 66.66666666666666
 >>> astable_duty_cycle(resistance_1=356, resistance_2=234)
 71.60194174757282
 >>> astable_duty_cycle(resistance_1=2, resistance_2=-1)
 Traceback (most recent call last):
 ...
 ValueError: All values must be positive
 >>> astable_duty_cycle(resistance_1=0, resistance_2=0)
 Traceback (most recent call last):
 ...
 ValueError: All values must be positive
 """

 if resistance_1 <= 0 or resistance_2 <= 0:
 raise ValueError("All values must be positive")
 return (resistance_1 + resistance_2) / (resistance_1 + 2 * resistance_2) * 100


if __name__ == "__main__":
 import doctest

 doctest.testmod()