This circuit was found in a 1980s Signetics documentation. The integrated circuit is from the era. The circuit enables coded matrix control via a toggle switch.
IDT ZSSC3230 Capacitive Sensor Signal Conditioner Available from Mouser Electronics stock, this IDT...
This circuit uses only two common transistors and provides good audio power in a speaker. Readers who...
This is the analog part of the previous circuit with the pressure sensor for the altimeter. The...