The frequency meter by use the LC resonance circuit that adjustable until the frequency show peak amplitude.
Include: Volt meters :: Sound level meter :: Analog vu meter :: Soil moisture meter :: Digital meter circuit diagram :: Temperature measurements :: Electronic measurement tools :: Frequency meters :: Best battery tester :: Transistor tester project
These are Five Battery low voltage alarm indicator circuits, as ideas to make small projects, them use LED display easy, cheap with normal parts look below [...]
This is the Transistor tester circuit into PCB. When your project do not works, the tester electronic parts or component be what need very much.