This circuit was obtained in a Popular Electronics of the 90s. The circuit uses integrated from the time, uncommon today. Note that the speaker has a higher impedance than ordinary speakers.
The indicated circuit uses an unusual buffer from National Semiconductor. The frequency is given by...
This battery charger is suggested by National and has a switch that turns it off when the battery is...
This circuit reinforces signals in a frequency range between 1500 and 2000 Hz for use in...