I have a queston about using a 28 pin ATMega8 for a tachometer cicruit. From what I can draw the AVR will handle all of the process in code, so all I need(major components) on the board is the LED display connected to the AVR? Or should I use a multiplexing/IC, I am using 6 sevenseg displays(six digits). What pin on the AVR would I have the pulses from the pick up go to? My pick up is a LED/phototransistor unit I built. Also do I need some sort of signal filter to boost the pulses before they go into the mega8? Thanks for all your help.

 

For 6 seven segment displays you will need an external multiplexor of some sort. There are 7segment decoder ICs available that might do the trick. Also take a look at LCD displays- the AVR should be able to generate all the timing signals for on of these. You can use just about any pin for the pulse input. Using a external interrupt will make your software a little nicer though. The pulses you input should be logic level pulses (0-5V or 0-3.3V depending on your power supply).

You should add an RS232 connector and Max232 type level shifter so you can talk to your PC for debugging. It will make your life much easier.

Brent