In this circuit the LED lights up when the voltage drops below the value set in the trimpot. The transistors can be the BC548. The circuit is from a 1999 American publication.
This metal detector circuit uses an AM radio as an indicator. The radio is placed off-station and tuned...
This oscillator produces a modulated signal using a unijunction transistor. We found it in an...
This transmitter was obtained in a 1953 publication. The original transistor was made of...