This simple circuit can work with either 4.5 V or 6 or 9 V if a 1k resistor is added in series with the set of LEDs. The circuit is from an old French publication.
The circuit presented in the figure is an amplifier for stereo sources with the Maxim MAX9723...
In fact, this 1994 circuit uses a scale of LEDs to indicate the pulse rate applied to its input....
What differentiates this circuit from the previous one (CB15613E) is the non-need to use a...