hunicombs:
i am making turn signals to make my UTV street legal. so the need to blink at a regular rate so far with my program using it on the arduino shield it works great i was going to mock it up and a bread boars tonight with out the shield to see how it works out.
If the board clock may be off by 3 or 4%, what is the legal range of turn signal blink rates? Legalese is a kind of code, it should detail or refer to details in another document -- between cool morning and hot afternoon most blinkers should drift, temperature compensation circuits cost money!
I'm a bit surprised you don't just have a 555 circuit and switches to do this.