## Intro: 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

*in series across the inductor.*

**voltage divider made of two capacitors**Remember **C**olpitts = 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.**

## 4 Discussions

1 year ago

Hated those when I studied them... Made a lot of Colpitts and Hartleys "Amps"... They wouldn't oscillate... But a great instructable :-)

Reply 1 year ago

Where did you study?

Reply 1 year ago

I studied in the late 70s, begin 80s in Aalst, Belgium... Quite a long time ago :-)

1 year ago

No doubt Colpitts would have loved to see the popularity of his circuit among the enthusiasts.