This circuit was obtained in an Electronics Now from the 90s. The circuit uses operational amplifiers from the time and the indicator is of the Sonalert type with internal oscillator.
This interesting circuit was found in a 1967 Japanese documentation. Transistors are types of...
This assembly circuit using a small motor as a generator was found in Radio Electroics magazine from...
This circuit is of great use today, when solar energy is becoming increasingly important. The...