Motorola suggests this circuit in an 80's documentation. The circuit uses an inverter to produce a higher voltage for 9 V battery charge from a single cell.
This circuit was found in Radio Electronics from the 90s. It uses a transconductance operational...
The UVTRON tube is an ultraviolet radiation sensor. In this circuit from Radio Electronics from...
This circuit can function as an output shield for microcontrollers, being compatible with TTL...