Make a Colpitts Oscillator!

The curiosity in this proyect is to show: How obtain a pure sine wave from a DC power source?

I found this beautiful circuit in www.learabout-electronics.org

Remember this is only a practical proyect and demostrative and all the credits except the pcb and probes are the same "bros" of learnabout-electronics! :)

The answer is a LC Tank circuit, that can make Oscillations in the time, and the oscillator that i made can do that :)

It's pretty simple to make and You can see in a electronic Scope, you can do anything with a sine wave.

The colpitts oscillatoir...

A Colpitts oscillator, invented in 1918 by American engineer Edwin H. Colpitts, is one of a number of designs for LC oscillators, electronic oscillators that use a combination of inductors (L) and capacitors (C) to produce an oscillation at a certain frequency. The distinguishing feature of the Colpitts oscillator is that the feedback for the active device is taken from a voltage divider made of two capacitors in series across the inductor.

Remember Colpitts = Tapped C (Capacitors)

The capacitor form in effect a single "tapped" capacitor is necesary to calculate the Total capacitancy (Ctot).

The values of the two capacitors (connected in series) are chosen for general rule 10 to 1 which means that C1 = C2/10.

Ctot= (C1*C2)/C1+C2

This gives the total capacitance necessary for the tank circuit to achieve "parallel resonance" at the requeried frecuency.

The oscillation frecuency is calculated by:

F resonance= (1)/(2*pi(sqrt(L*Ctot))

pi= 3.1416

L=inductor value in Henrys

Ctot=capacitor total equivalency in microfarad usually

*The individual values of the C1 Y C2 are choosen so that the radio of the values produces the necessary proportional feedback signal to maintain the oscillation estable.

*The ratio of the voltages across the capacitors in series is in inverse proportion to the ratio of the values, this means: Smaller capacitor values has a larger signal voltage and viceversa.

One method of oscillator analysis is to determine the input impedance of an input port neglecting any reactive components. If the impedance yields a negative resistance term, oscillation is possible. This method will be used here to determine conditions of oscillation and the frequency of oscillation.

Here it is the original circuit from the page.

Calcules:

Ctot= 3nF = 0.000000003 F

fosc= 1 MHz

Construction of the inductor:

L=8.44 uH= 0.0000084 H

Simple inductor ecuation design for practical circuits:

L(uH)= (D(n)(n))/((nd/D)+0.44)

*Requieres to add 10% of spires more for adjusts.

D=Internal diammeter of the inductor

n=number of spires

d=diametter of the wire = AWG *(See the table for differents coil diammeter and equivalents).

NOTE:

If you want to choose a different frecuency for your purposes, you have to use the formula for Frencuency of oscillation in the image above, the other values of the circuit doens´t care.

Here is the final circuit ready to print and make your own colpitts oscillator!

I put a video in the instructable for demostrative pruposes!

:)