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Support Forum » First project in the Nerdkits Manual

July 10, 2011
by tombuss2000
tombuss2000's Avatar

I am working through the temp sensor program logic right now. I have a question that I think I know the answer to but not sure. I am learning here.

Why did they scale the process clock down by a factor of 1/128? I think it's because the temp sensor has a response time of no more than 20 milliseconds (from the chart in the temp spec manual) which means it can respond 50,000 time per second.

50,000 is about half the speed of 115kHzs but is the slowest processing speed available? There is still some mismatch there. Am I dumb here?

July 11, 2011
by hevans
(NerdKits Staff)

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Hi tombuss2000,

Your initial thought is close to the right answer. It is not the LM34 that is the limiting component here though, it is the ADC inside the chip. If you take a look at page 248 of the ATmega168 datasheet you will see the ADC requires a clock frequency between 50KHz and 200KHz for maximum resolution.

Humberto

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