A simple oscillator which may be used for code practice. In order to have sufficient inductance to produce an audio frequency, an iron core transformer such as used in audio transformer-coupled amplifiers is hooked up as shown.
The major functional blocks necessary to design a general purpose audio oscillator, and give all the details of my current prototype. Implementation is in the mode of an analog computer, since the desired outputs are sine and cosine values as a function of time. The following snapshot shows my prototype connected to an X-Y oscilloscope, to display a Lissajous pattern.