Another CPO: Cheaper Beeper

I’ve been busy plugging away at my DDS/Arduino/VFO for 630m (more on that later), however yesterday I came across a neat little circuit for a code practice oscillator.

Cheaper Beeper CPO

Cheaper Beeper CPO

I’ve still got my previous CPO, however the simplicity of this one appealed to me. It’s two transistors, two resistors and a capacitor. All on a small piece of perf board.

In the image above, you can see the 9V battery connector. At the bottom are the two wires for audio out. And then in the middle there will be two more wires for the cw key. My plan it to mount it all in a small box with two 3.5mm mono ports – one for audio out and one for the key. That way I can either feed the audio into my computer for practice or into a speaker.



I’m thinking I may still build another CPO yet, as I really would like one with a sine wave – the square wave is a bit harsh and annoying. Plus, one with a sine wave I could wire into my FM rig for some code sending practice – if I find someone else so equipped. (I think sending the tone of these guys over the air would probably drive me and my practice partner nuts – not to mention anyone listening!)

Anyway, if you’d like to build one of these little guys yourself, the instructions can be found online here at the ARRL website. However, a word of caution.

There is a minor error in the schematic. If you’re rushing through trying to build the thing up quickly after work it may bring you unstuck – as it did to me. The PNP transistor in the schematic is marked as a 2n3904, however it is in the parts list as a 2n3906. Now a quick check would show that the correct one is the 2n3906, but if you just look at the schematic and go barging in blindly, well it wont work.

Anyway, enjoy! If you build one up send me a photo! 🙂

Sacrificial transistor - should've checked.

Sacrificial transistor – should’ve checked.


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