Freeze Alarm (CB14454E)

The circuit of a 1968 publication can be implemented with more modern transistors such as BC548 for NPN and BC558 for PNP.

Receiver via power grid (CB5068E)
This receiver can be used to receive signals from the previous circuit transmitter. The circuit is...
STHVDAC 256MTG Antenna Tuning Circuit (COM091E)
September 2016 - It can be purchased from Mouser Electronics the new antenna tuning circuit from...
Infrared receiver (CB7822E)
In the figure we have an infrared receiver circuit using an operational 741. The circuit is an...