555 Design Assistant

    Given the recent contest at Hackaday.com, as well as my recent use of the 555 timer on the Knight Rider Scanner, I decided to put together a simple program to ease in the design of 555 timer circuits. Version 1.0 contains probably the 3 most common uses: Astable, MonoStable, and modified Astable allowing for duty cycles of less than 50%.
    This program is free to use in the hopes that it helps others understand a little better the 555 timer. I have also included the formulas used in the program if you wish to see how it is calculated.

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    The astable circuit allows for varying R1, R2, and C. The program then calculates Frequency, Time on (t1), Time off (t2), and the duty cycle. It also generates a theoretical waveform to visually see the shape of the output.

    The modified astable circuit is the same as the astable with the addition of a diode across R2. This allows for a <50% duty cycle. The capacitor charges through R1 and the diode, and discharges through R2.
    Because of this, the charge time to 2/3 Vcc is dependent on the voltage of Vc + Vd (capacitor voltage + diode voltage). Since the diode voltage is constant, it must be considered in the charge time.
For example: a 5V Vcc with a silicon diode(.7v) means a Vc of 2/3Vcc - .7 = .66 x 5 - .7 = 2.63V (3.33V no diode or 21%)
    with a 10V Vcc, 2/3Vcc x 10 -.7 = 5.97V (6.66V no diode or 10%)
Therefore, the smaller the Vcc, the greater the impact.

Finally, the monostable circuit takes a signal pulse in, and creates a pulse width output of R x C.

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