This circuit, from a Motorola manual, uses transistors from the time, but can be implemented with a BC548. The diodes are general-purpose, and the power must come from a source or battery since consumption is low.
This circuit, from a Motorola manual, uses transistors from the time, but can be implemented with a BC548. The diodes are general-purpose, and the power must come from a source or battery since consumption is low.