Introduction: 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.
Step 1: Theory and Operation Principle.
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.
Step 2: Oscillation Conditions.
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.
Step 3: Schematic and PCB.
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.
