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Topic: Very Small Arduino (Read 16315 times) previous topic - next topic

cyclegadget

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So there are multiple connections, but only one ground plane


If I counted correctly there are 21 spots to connect ground pins or headers to, and they are all the same ground / GND.



   I have found the extra ground pins very handy for running lots of LEDs without a bread board. I at first thought the extra grounds took too much extra board space but, now I realize that trying to make up extra ground area would have been a major pain.
Good links: Eagle tutorial= http://www.youtube.com/playlist?list=PLDE1858BD83D19C70
General Arduion tutorials = http://tronixstuff.wordpress.com
http://www.gammon.com.au/forum/bbshowpost.php?bbtopic_id=123

fm

Yeap, not enough space on that small board to have separate ground planes. Mind you, the original Arduino is much, much bigger with several ground pins and no ... no separate ground planes, not even a filtered analog supply.

The vinciDuino however does have separate ground planes for analog and digital and supply is nicely filtered out.
   

funkyguy4000

Filters, wait wha wha what?  I'm confused, you need a filter for the ground?
Accelerate to 88 miles per hour.

fm

What I meant was, that the vinciDuino has separate ground planes for analog and digital joint at a star point on the board. For the analog supply of the AVR it has a small filter.

After reading the wording it does lead to confusion, sorry.
   

funkyguy4000

ohh okay.

So why would one want a different ground plane for analog and digital?
Accelerate to 88 miles per hour.

johnwasser


So why would one want a different ground plane for analog and digital?


To keep the switching noise associated with digital circuitry out of the analog conversion hardware and thus reduce noise in the inputs.
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fm


ohh okay.

So why would one want a different ground plane for analog and digital?

Ummmm a bit of a long story, but the analog world doesn't like very much the switching noise generated by the digital world.

On mix-signal chips or in this case an AVR on its ADC, you end up loosing the least significant bits due to noise. How much? It very much depends on the application, but if there is a lot of switching activity or switching big loads it will be fairly big. I've measured on some stock Arduinos that you loose the 3 LSB on 10bit ADC reading due to noise. You are loosing about 19 dBFS of the 62 dBFS of its dynamic range, i.e. your noise floor would be at about -44 dBFS. All this translates into: if you used a 7 bit ADC you would get the same result. Not bad at all! So if your ADC has a 5V reference, signals that change less than 40mV would be blurred with noise. Is that bad? Well, it depends on the sensor, amplifier ... and your application.

Having a separate analog and digital ground plan joined at a star point helps significantly by having both these worlds separated (the quiet and the loud).
   

funkyguy4000

makes sense, what is LSB?
Accelerate to 88 miles per hour.

fm

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