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 old documentation, however the components used are common today. The...
This circuit is from a 1964 Electronic Design. The sensor is an LDR and the transistors are...
This circuit from Delta Products was published in the May 1974 Radio Electronics magazine. The...