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Atmega328p ADC & CPU frequency
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Please be positive and constructive with your questions and comments.

Re: Atmega328p ADC & CPU frequency

by tcharron on Sat May 29, 2010 9:07 pm

That's a reasonable thing to check, and I have been meaning to get back to this project. The weather outdoors is much improved from when I was last playing with this, and my attention has been elsewhere.

I have tried to use both a wall-wart supply, as well as powering the device via USB from my laptop computer, and did not have material differences. Perhaps the easiest way to test your theory is to use a battery as a power supply for the atmega/tmp36 and see if my results vary at all. I'd have to do some research on filtering devices before I can whip together a filter. I do have an oscilloscope but it's in the basement under a thick layer of dust.

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Re: Atmega328p ADC & CPU frequency

by didier on Sun May 30, 2010 3:51 am

Look, the power supply itself has a low concern for that, except for what is regarding its impedance. The critical point is the µP itself as asource of noise. In this cas, the groung plane design as well as the power supply path are important. I'll try to find articles on that; many datasheets for sensitive device contain valuable information.

Wheather is awful these days, thus a little bit more presence here :mrgreen:

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Re: Atmega328p ADC & CPU frequency

by fat16lib on Sun May 30, 2010 9:01 am

The TMP36 is really easy to use and in typical hobby environments noise is not the main problem. Your posted results don't look like you have a noise problem that would explain the strange behavior. I am not saying it isn't noise but I have mostly seen people have ADC/analogRead() problems with the TMP36.

If you have a reasonably good multimeter connect it to the TMP36 with the Atmega328p and compare the results at each frequency. This should at least give some new info.

Better yet verify that the ADC readings make sense by comparing the ADC readings to a multimeter using something like a 10K pot between 5V and GND. Do this at each CPU frequency.
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Please be positive and constructive with your questions and comments.