AVR-Chat

Thanks for confirming.  As for other techniques, I thing I'll just stick
with the simple voltage divider, turning it on only to sample.  I've already
bread-boarded up the divider/dual-mosfet thing and it works just fine.
Steve

 

From: AVR-Chat@yahoogroups.com [mailto:AVR-Chat@yahoogroups.com] On Behalf
Of Graham Davies
Sent: Saturday, December 15, 2007 6:08 AM
To: AVR-Chat@yahoogroups.com
Subject: [AVR-Chat] Re: ADC Vref

 

--- In AVR-Chat@yahoogroups.com <mailto:AVR-Chat%40yahoogroups.com> ,
"Steven Hodge" <stevehodge@...> wrote:

> In Graham's post he says "To turn
> the whole thing on, we apply a high
> level to the drain of the N-channel."
> I assume he meant to the gate, not
> the drain?

Argh! And I read that post through THREE TIMES before I sent it! Yes, 
yes, gate not drain.

Now that we know more about your application, it's clear that other 
solutions would work equally well (including those that sacrifice some 
accuracy). For example, you could have a voltage divider with high 
value resistors to get a very low (but continuous) current and use an 
op-amp in voltage follower configuration between that and the 
microcontroller. Power the op amp from a port of the microcontroller 
and turn it on only when you need it. A multi-megohm resistor between 
the supply and your circuit would go a long way towards protecting it 
from damage and the tiny current when the op amp is off would surely 
just bleed harmlessly away.

As this is a one-off, what you end up doing might have a lot to do with 
what you have in your parts drawer so the fun can continue and we can 
collect more ideas.

Graham.

 

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