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From: Rich Webb
Subject: Re: digital voltmeter and ammeter
Organization: Line Eater Memorial Fund
References: <3E2AB7F8.firstname.lastname@example.org> <3E2ACBE3.email@example.com> <3E2AF137.firstname.lastname@example.org>
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Date: Sun, 19 Jan 2003 20:05:49 GMT
NNTP-Posting-Date: Sun, 19 Jan 2003 15:05:49 EST
On Sun, 19 Jan 2003 18:40:33 +0000 (UTC), Alex Graham
>I forgot to mention that my charger is switch mode. Will this mess up
>the voltage reading as far as the ADC is concerned?
>Bill Sloman wrote:
>> "Alex Graham" wrote in message
>>>Thanks for your suggestions.
>>>Im trying not to make this _too_ complex, it being an A level project
>>>(last year of school), so what Im really trying to do is simply use an
>>>ADC that I can plug into a protoboard and get cracking with...
That's the whole purpose behind integrating the ADC into a
microcontroller -- it really does simplify things considerably. Often
you can kick off a conversion and do other things. When the conversion
completes you get an interrupt (or poll for a flag bit) and read the
results from a register or two. Interfacing to an outboard ADC adds
complexity. You could probably piece together enough discrete logic
chips to control, read, and display the results from a stand-alone ADC
but it would be unnecessarily messy. *Possibly* a CPLD but then you get
into programming again.
The advantage of a roll-your-own approach with a microcontroller versus
a more integrated controller is a considerable cost savings, balanced
against a more complex development process.
Nevertheless, probably your simplest way to do this using an ADC-type
sensor would be an integrated module like a PicStic. It has all the
elements but you still need to program them. A nice thing about the
PicStic is that it directly communicates with a 4x20 LCD display and
matrix keypad. It also includes routines to handle the ADC grunt work.
Summary at http://www.micromint.com/app_notes/picstic4_summary.htm
WRT the switcher. Yes, it will add noise. Yes, you'll need to deal with
it by using an analog anti-aliasing (low pass) filter on the front end
as well as (probably) a digital filter on the back end.
Rich Webb Norfolk, VA
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