A/F gauge schematics are all over. They're painfully easy to make, as practically all use a LM3914 LED-bar driver IC. The datasheet for the LM3914 will have a circuit that does exactly what you want.
Tach is a bit more complex, as you're converting frequency to volts. It too can be made with an LM3914 (or two, or three etc.) once you've got the voltage signal, though. Search for frequency to voltage converters.
Tach is a bit more complex, as you're converting frequency to volts. It too can be made with an LM3914 (or two, or three etc.) once you've got the voltage signal, though. Search for frequency to voltage converters.
