Monostable Oscillator with Range from 0.1Hz to 100kHz

The objective of this project is to get a square wave with a variable frequency from 0.1Hz to 100kHz.

To achieve this, we'll make use of a jumper that connects different arranges of capacitors to the NE555 integrated circuit so the resulting frequency range can vary.

This oscillator has 6 frequency ranges.

Range	Pin number
0.1Hz - 1Hz	1
1Hz - 10Hz	2
10Hz - 100Hz	3
100Hz - 1kHz	4
1kHz - 100kHz	5
10kHz - 100kHz	6

In order to get this ranges, we start from the generic 555 oscillator:

Pasted image 20241123192249.png

Here, the individual times required to complete one charge and discharge cycle of the output (VO1) is given by the resistors Ra, Rb and the capacitor C1 as follows:

\begin{aligned} t_{1} = 0.693 (R_{a} + R_{b}) & t_{2} = 0.693 (R_{b}) (C_{1}) \end{aligned}

Where, R is in Ohm’s and C in Farads.

And the frequency (T) is given as follows:

\begin{array}{r} F = \frac{1}{T} \end{array}

Where, F is in Hertz and T is in seconds.

We're going to start from the maximum desired frequency for the oscillator, 100kHz

\begin{array}{r} F = \frac{1}{T} \end{array}

\begin{array}{r} T = \frac{1}{F} \end{array}

\begin{array}{r} F = \frac{1}{100, 000 H z} = 1 x 10^{- 5} s e c o n d s \end{array}

From this, to make a roughly we'll divide this time between the ON time (t1) and the OFF time (t2).

\begin{aligned} t_{1} = 6 x 10^{- 6} s e c o n d s & t_{2} = 4 x 10^{- 6} s e c o n d s \end{aligned}

Since it's easier to variate a resistor, we'll propose two of these resistors and calculate from there the needed capacitance required to fulfill the frequency band.

\begin{aligned} R_{a} = 50 Ω \end{aligned}

And from there we need a second resistor that has a minimum value so it won't ever reach the value of zero ohms and add a variable resistor so we can go from the minimum frequency and the maximum frequency.

From here, we'll calculate each condenser so it matches the frequency range to each resistor.

Pasted image 20241123202132.png

Schematic

Pasted image 20241123201652.png

Where the frequency range is determined by a equivalent capacitor (Ceq), which is connected through a selector jumper.

Cover	Title	Description
	Monostable Oscillator Circuit Front Side	This is the finished 555 circuit oscillator. There is a LED indicator and an output to take that signal and use it in other circuits!
	Monostable Oscillator Circuito Back Side	Te back of this circuit was coated with stain to it wouldn't rust away.