1. Home
  2. Hobby Electronics Basics
  3. How to build a simple LC oscillator

How to build a simple LC oscillator

Hello !

I'm new to analog electronics (although I've been using uCs for a while) and I'm trying to build a really simple RC oscillator, a Hartley or a Colpitts one. All the schematics I've found on the web or in books are using complex and additionnal components (like 4 pins MOSFETS, JFETS, transformers...). The two or three models that I've tried to build weren't oscillating at all. I want to keep it simple to be able to fully understand what's happening (otherwise I'd have used somme xtal or IC).

Do you know some simple LC oscillator schematics using standard components that would simply oscillate at few MHz ?

Thanks

Reply to
Alexis Bezverkhyy
Loading thread data ...

A phase shift oscillator using a regular low-cost transistor? Figure 2 shows it:

formatting link 

--
Regards, Joerg

http://www.analogconsultants.com/
 Click to see the full signature
Reply to
Joerg 

--
9V>-------+------+
          |      |
 Click to see the full signature
Reply to
John Fields

If you want a simple OSC and make your own coil, look at a Armstrong Oscillator.

That has what is called a tickler coil, another coil is wound on the same form as the feed back etc.. We use a armstrong variant osc that generates 100Khz at 250 K watts. It's all one tube!, Very simple.

formatting link
"

Reply to
Jamie

A good healthy bypass cap from 9V to ground is probably essential -- John forgot to mention it because he bypasses _everything_ (I'm sure).

--
Tim Wescott
Control systems and communications consulting
 Click to see the full signature
Reply to
Tim Wescott 

--
I\'m sure you didn\'t mean to say that I let everything go by unheeded, so
thanks for the kind words and yes, I mostly do. :-)
 Click to see the full signature
Reply to
John Fields

I'm completely swamped with work that makes me money (thank goodness!), but send away if you can get the PCB to fit into an email (gawd I'm being a smartass tonight).

--
Tim Wescott
Control systems and communications consulting
 Click to see the full signature
Reply to
Tim Wescott

Thank you a lot, this is what I was looking for ! I'll try to build them tonight.

Reply to
Alexis Bezverkhyy

If you will be using this to drive digital circuitry, you can build simple RC oscillators with CMOS gates that have clean rectangular outputs. Requires 2 inverter stages (or NAND or NOR with appropriate inputs ties high/low), one C, and 1 or 2 Rs. See Don Lancaster's "CMOS Cookbook" page 225. (At least, it's page 225 in my ancient edition.)

In fact, if you have a Schmitt-trigger gate like a CD4093 you only need one gate: Tie one input high, put your C from the other input to ground, and the R from that input to the output. Simple!

Best regards,

Bob Masta DAQARTA v4.51 Data AcQuisition And Real-Time Analysis

formatting link
Scope, Spectrum, Spectrogram, Sound Level Meter FREE Signal Generator Science with your sound card!

Reply to
Bob Masta

I've just succeeded in building the phase-shift oscillator (fig. 2). I did it with a 2N2222 which seems to be almost the same as 2N3904, but the setting of R6 was quite subtle to make the circuit oscillate. I could finally probe the RC network with a scope and understand how it works !

I'll try John's circuit tomorrow.

AB

Reply to
Alexis Bezverkhyy

The hfe for the 2222 is quite poor at low currents, see if you have some small signal BC-type in your junk box. Those are more popular in Europe.

Hey, but at least it worked.

--
Regards, Joerg

http://www.analogconsultants.com/
 Click to see the full signature
Reply to
Joerg

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.