Old phones with dials can be used in a simple home intercom system, as this circuit from Popular Electronics from the 90's shows.
This circuit can be used with receivers to attenuate signals that may cause interference. The...
This circuit is from a Linear datasheet. The circuit provides a 5 m voltage with 40 mA from an AA...
Found in a Popular Electronics from the 90s, this game can be seen in other configurations on this site. The...