AVR-Chat

I have also been in a situation where I needed to read a pot with modest requirements... something like reading a brightness pot and dimming a display using the color lookup table palette on a pc104 app. I actually have a program that will read a pot charging a cap on a regular old input pin. The cap charges thru the variable resistor. I assume it goes hi at the logic threshold voltage. Then you change it to an output and discharge the cap. I used log and exp and a bunch of fp because it was on a pc. I guess you could use fp on a big avr to prove the concept, the make a table of time to charge cap vs resistance. Something like vcap = 5v*(1-exp(t/tau) where tau is the pot R and the cap value. Need to solve for R given t. This is doable in c no prob. Lets keep working on it. Do you need more than 6 bits? 



-----Original Message-----
From: Marc R.J. Brevoort <mrjb@dnd.utwente.nl>
To: AVR-Chat@yahoogroups.com
Sent: Fri, Nov 27, 2009 4:26 pm
Subject: Re: [AVR-Chat] C version of AVR400?


On Mon, 23 Nov 2009, BobGardner@aol.com wrote:
> Thats a really minimal a/d converter...
 its only 6 bits, doesnt have much range.
 If you had an 8 bit spi d/a converter you
 could use the analog comparator and have
 a nice accuate 8 bit successive approximation
 a/d with a real 0-5V range.
That would mean ordering in DAC chips. But the
olution feels 'chunky'. Using a DAC chip just
o that I can do ADC using the analog comparator?
'd rather just buy an ADC chip then. But if
'm going to get additional components anyway,
t would make more sense to me to choose a
ifferent AVR- one that already has an ADC
or several) built-in.
Thanks for the suggestion, though.
Best,
arc

-----------------------------------
Yahoo! Groups Links
   Individual Email | Traditional
   http://docs.yahoo.com/info/terms/



[Non-text portions of this message have been removed]