Schematic for a good AVR power supply

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Psychlow
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Posted by Psychlow: Tue. Nov 13, 2007 - 03:37 PM
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I was wondering if anyone has a good schematic for what a good AVR power supply should look like, assuming input from a noisy 10-15VDC source (like a wall transformer) along with components for decoupling/reducing noise on ADC channels (AVcc, AREF when using internal voltage source, etc.)

I'm having an issue going from the STK500 to a breadboard - no matter how I set my power supply up with decoupling capacitors and such, I can only get an ADC accuracy of about +-0.1V where on the STK500, I can get within +-0.04V.

Thanks in advance!

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Learning and Information, General Electronics
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S-Sohn
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Posted by S-Sohn: Tue. Nov 13, 2007 - 04:24 PM
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Look at the application note AVR042: AVR Hardware Design Considerations

Regards
Sebastian

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leon_heller
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Posted by leon_heller: Tue. Nov 13, 2007 - 05:05 PM
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It's a waste of time trying to get the ADC working properly on a solderless breadboard.

Leon

Leon Heller G1HSM

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Kleinstein
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Posted by Kleinstein: Tue. Nov 13, 2007 - 10:18 PM
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With some extra shielding, low noise circuits are possible on a breadboard. Having the breadboard mounted on one half of a large metall cookie box, make a really nice shield. This way one can even reach the noise limit of a 16 BIT A/D, most printed circuits in a plastic case are worse.

Regulating a wall-plug 12 V to 5 V or whatever one needs for an AVR, a simple 7805, LM317 or similar regulator is good enough. Just make sure that all the needed capcitors are there. Getting a stable (except +-1) reading from the 10 bit AD should be no real problem.

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Psychlow
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Posted by Psychlow: Wed. Nov 14, 2007 - 04:02 PM
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leon_heller wrote:
It's a waste of time trying to get the ADC working properly on a solderless breadboard.

Leon, what is the reason for this? Just the fact that there's not an effective way to reduce EMI/RFI?

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Kleinstein
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Posted by Kleinstein: Wed. Nov 14, 2007 - 06:29 PM
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Problems with breadbords are the large capacity betweeen contacts, high inductance of some connctions and a relativly high an not very reproducible contact resistance. From this only the last is realy a problem for slow AD circuit. For high frequency circuits that combination is a desater.

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vector86
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Posted by vector86: Sat. Nov 17, 2007 - 09:16 PM
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If you google STEPS, it's an extremely low noise\distortion audio power supply for headphone amps. I think it can be tweaked to power an AVR circuit.

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