We found this circuit in a Hands-On Electronics from the 90s. The circuit must be connected to an external amplifier. Frequency control is capacitive, using an antenna for this purpose
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...