This is an audio demo of using this circuit here: http://i.imgur.com/YDBlJST.png ( you can also click on the picture to the left and it will pop up another larger view of this circuit) as a morse code practice oscillator powered only from the voltage contained in all soundcard mic jacks.  A simple square wave generator is used, LM3909, and uses AUDIO to MIDI technique to recreate the cw audio tone.  This audio file starts by sending cq 3 times without the AUDIO to MIDI system and then followed by 3 cq's with the AUDIO to MIDI system engaged, so you can hear how effective using the AUDIO to MIDI technique is at creating a great morse code practice oscillator on you computer.  For more info see this article: http://qrqcwnet.ning.com/profiles/blogs/code-practice-oscillator-powered-by-any-computer-mic-jack-no-batt

Morse code oscillator circuit powered by the computer MIC JACK VOLTAGE

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