AVR-Chat

It depends on the accuracy YOU need. There are several
factors that contribute:

1. The referemce
2. The ADC conversion accuracy
3. The external circuit accuracy

If you use all 10 bits, then you can resolve 1 part in
1000, basically. 

But, if you use the internal reference, you are within a
few percent, at best. If you use Vcc, you are within the
accuracy spec of your supply (5% or worse, usually). You
can get external references that will do a lot better than
1% (but you have to pay for that precision).

If your reference isn't better than 1%, you won't get 1%
with 1% resistors. 

Jim
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I'm just starting to play with the ADC capabilities of the AVR... Are 1% resistors what everyone uses, or do I need something more precise?

 - jim

At 07:43 PM 1/20/2005, James Washer wrote:


>I'm just starting to play with the ADC capabilities of the AVR... Are 1% 
>resistors what everyone uses, or do I need something more precise?

It all depends..

There's all kinds of fun to be had in precision land, but remember, every 
resistor is exactly what it is.. It may be marked 10,000 ohms, and actually 
be 10,050 ohms, but a meter can sort that out for you.

I use 1% resistors in some designs, and 5% in others, it depends on the 
relative cost and availability, against what I'm trying to accomplish.

--- In AVR-Chat@yahoogroups.com, James Washer <washer@t...> wrote:

> I'm just starting to play with
> the ADC ... Are 1% resistors
> what everyone uses ...

Are you sure this is what you want to know? In my case, yes, I use 1% 
resistors in analog circuits around the ADC. But your needs may be 
different from mine.

> ... or do I need something more
> precise?

You say "play", so I think the answer is no, use 1%. To properly 
answer the question, we would need to know what you are trying to do 
and what your circuit is (i.e. how many resistor tolerances are 
adding up in your error).

It has been suggested that you can use a meter to measure the 
resistance accurately. Many meters have accuracies of less than 1% 
and if you are "playing" this is probably what you have. Take a look 
at your meter specs before you trust its reading more than the 
nominal value of a 1% resitor.

Graham.