Found in a Popular Electronics from the 1990s, this circuit is a 1-digit counter that advances under the command of S2. The circuit can be expanded to more digits.
In the figure we show how to implement a voltage reference with the ON Semiconductor rail-to-rail...
This circuit is from a technical documentation from 1978. The maximum output current is of the...
This RF and audio follower applies its signals to a small amplifier. The FET can be any...