After building the circuit the sound produced was very distorted and unlike the slow whoop I was expecting. The LED connected to the first chip performed as expected with about one pulse per second. After inspection of the circuit I noticed that the 100 ohms resistor in series with the speaker had become very hot. I changed it for a resistor of 180 ohms and now the circuit worked fine. I substituted a 10K potentiometer (see images below) for the R7 resistor (1K) which made some interesting changes in the slow whoop (higher or lower pitched).
At this point in the book I believe the use of an oscilloscope would become interesting even helpful. I would be able to analyse the waveform on several pins of the circuit. The oscilloscope is however an expensive piece of equipment which I don't own yet. It will put it on my wishlist. Something I noticed with this hobby that there appears to be an ever increasing need for space, equipment and components.
A video of the experiment, with several tweaks of the circuit, is available at https://www.youtube.com/watch?v=d_ADg2LS3fA
|Complete circuit of figure 4-30. R7 is substituted with a 10K trimmer.|
|Close-up of the circuit.|