This circuit was found in a 90s Popular Electronics. It generates tones given by the oscillators and can be changed. The circuit already includes an amplification stage.
August 2016 - It can be obtained from Mouser Electronics, Modules Intel Curie low power containing...
This circuit was found in a 1965’s General Electric documentation. It is intended for low voltage...
This transformerless 16-ohm speaker circuit was found in a Radio Electronics from October 1963. The...