Daily Archives: September 28, 2010

Me and the Cap’n

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So, it turns out that clock crystals need a “load capacitance” between each of their two pins and ground. I’m not entirely certain what these capacitors even do, but I do know that they are critical to keeping good time.

That nixie tube clock that I made originally had a clock crystal in it that had no load capacitors. This resulted in it being inaccurate.

Tik Tok

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I have a clock!

So last night/today, I worked on getting the clock part of my AVR working. Here’s the basic rundown.

The ATmega48A has what’s called an asynchronous timer. A timer usually works by simply incrementing a number on a fixed interval of time and doing something special when that number reaches a certain value. Most of the time, the timer will just increment every time the processor’s clock ticks. An asynchronous timer is special in that it can clock along at an entirely different pace.

While the processor is chugging along at 8MHZ, my clock timer is clicking along at 32.768kHz. How do I know this? Because I have it connected to a 32,768Hz clock crystal. Why such an odd number? Lemme explain.