I'm not sure how the guage type tachs work, but this is how I would build one:

Pulses from the coil are recieved by a digital counter circuit based on the 555 Timer IC. The counter circuit determines how many pulses per how much time, and converts that into a binary number (which is the RPMs).

If you want a digital display, you just send that binary number representing RPMs to a display driver IC which converts it to decimal on the LCD or LED display.

If you want an analog display (conventional tach with needle) then you send the binary number which represents RPM to a DAC (Digital to Analog Converter). The signal is converted to analog (low voltage = low RPM, high voltage = high RPM). The analog signal is sent to a standard gauge which is nothing more than a coil of wire, a magnet core, and a needle.


Oh, and one more thing:

WE WANT PICTURES OF YOUR PROJECT!!!


[addsig]