Using a 555, this configuration appears elsewhere on this site. This is from American documentation from the 90s. The indicator can be an LED or some device controlled by a relay.
In the figure we have a simple way to have a peak bargraph indicator. The amplifier is of the...
This amplifier of some watts with transistors in complementary symmetry NPN is from a Japanese...
This speed control for motors up to 500 mA was obtained in an old European documentation, but it...