Mega8 without external crystal. Problems or OK?

I'm working on a project to build an optical tachometer. I've got a couple mega8's to use on this.

As I've been drawing the schematic in Eagle I'm wondering how much trouble would I be making for myself if I were to leave out the crystal and caps and instead use the internal crystal in the mega8. My thinking is less components to have to lay out on the schematic and PCB.

As this is using time functions for counting would I be making trouble for myself?

I saw a blog post from TodBot about making a minimal Arduino with a mega8. I realize I'd need to add an entry into the 'boards' file for the IDE that would deal with the lack of external timing.

As always, thanks in advance.

Atmel guarentees the oscillator is ±10% when it leaves the factory. It can be tuned to better then ±1%. The oscillator is measurably effected by supply voltage and temperature (but stays within ±1% at room temperture). I've had trouble using Serial if the processor is more than ±4.5%.

Thanks for the reply. After reading some other posts here I am considering replacing the Mega8 with a tiny85. I'd like to use the internal oscillator if I can. My tach takes a signal in on a digital pin and outputs the data on the I2C bus. The max input would be not more than 200 pulses/sec.

I do use millis() to keep track of time for pulse counting.

So now I am looking at my options and would like to hear suggestions.

You'll only going to get an enthusiastic thumbs-up from me. I'm a big fan of the 85 processor.

This is the core I'm going to recommend... http://arduino.cc/forum/index.php/topic,51984.0.html http://code.google.com/p/arduino-tiny/

You can find a list of other cores and resources at that website.

You'll want TinyTuner from that site as well.

Thank you.

I spent waaaay too much time reading everything I could find via the forums about the tiny85 etc. I've got a couple t85's on order from Mouser...

If I can get this to work I will be replacing the atmegaxx8 with the tiny.