Very Simple Oscillator

Posted by on April 17, 2010

This is the first oscillator I ever built. I remember looking at books and magazines, schematics on the net, etc. They were all either colpitt or hartley oscillators. Generally speaking while they’re simple enough, they require the use of proper inductors which is something that usually you don’t have when you’re just starting out or you can’t measure them because you don’t yet own the proper equipment (unless you’re lucky).

As to avoid frustration, you should ignore them for now and take a look at simpler oscillators like the one that follows:

( This schematic is also available in PDF: Very_Simple_Oscillator )


This one is based on a cheap mosquito repellent, however the frequency was modified to a lower audible region, this is indeed an audio oscillator.
The output wave:

If you want something even simpler, you may take a look at “negistors” — however you will need a much higher voltage than 3V so it may not be possible to operate it in a portable device, unless you were to use two 9V batteries (and this to me wouldn’t be cheap nor practical!)

List of materials:

  • 1x 100K Resistor (1/4W)
  • 1x 10nF Capacitor (Ceramic or any other type)
  • 1x 3V Cell (use a button cell or two 1.5V batteries)
  • 1x BC548 (Or any other general purpose NPN transistor)
  • 1x BC558 (Or any other general purpose PNP transistor)
  • 1x 8 Ohm Speaker (any low power speaker will do)
  • 1x SPST Switch or Push button (optional, highly recommended)

Note: this oscillator will generally work reliably with voltages down to ~1.0V

If you want to operate the oscillator at higher voltages, you’ll have to replace the transistors with higher power devices such as the BC337 and the BD140. These should allow you to run it up to 12V (although the BC337 may run hot!)

The total cost is just pennies, considering you may already have a suitable speaker, switch and button cell which are arguably the most expensive components in the list.

Have fun building it!

Cheers.