This circuit that generates a special sound was found in a Popular Electronics from the 90s. The base is the 555 and the transistors admit equivalents, and a power stage can be added.
This circuit was found the Optoelectronics Sourcebook by Texas Instruments. Any phototransistor...
This keypad telephone encoder circuit was found in ancient American documentation. The components used...
This simple alarm with latching uses a relay as the main element. The circuit is from a Radio...