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-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Ole Petter Rxnningen
Sent: Saturday, August 26, 2000 14:59
To: PICLIST@MITVMA.MIT.EDU
Subject: [PIC:] Floatingpoint multiplication, conversion etc..


(Reposting, forgot the brackets. Sorry.)

Hi all.

I am about to embark on my first project, so please be patient.. (BTW, I've
read the FAQ, but didn't really find the answers I was hoping for)

I am planning to make a two-channel powersupply (0-25VDC), with a
voltmeter/amperemeter (one for each channel) on a 16x2 LCD display. I havent
chosen wich chip to use yet, BTW, I was hoping to get some clues here..

1. From what I have gathered, all I need to do to use a 16xxx to measure
voltage is to reduce input voltage with a couple of resistors (anyone have a
comment/good design?) on an ADC to 0-5VDC, and read off the byte from the
register. Measuring current should be similar, except a different 'reducer'
would be needed(? hints anyone?) Here is my first question:

I would like to keep the ground on each of the channels separate. As far as
I have understood, I should be able to use RA3 as ground on the circuit
beeing measured, and measure voltage on another pin. If I am right, all is
well. But since I have 2 channels, are there any chips I can use so that I
can have two different "grounds" on two different AD's? (Well, 4 different
ADC's in two pairs, I guess; one pair for Volt/Amp on one circuit, and one
for the other. Unless I am mistaking..?)

Are there any chips that can do this? (using two separate pins as ground for
two*two other ADC's)

2. After I have sucessfully read a byte from ADC, I need to multiply that
with 25/256 to find the voltage (or xx/256 to find the amp). I'd like to
display the resulting number (16bit FP?) on the display, and so I need to
convert it to an ascii string.. (Preferably in the format of xx.xx.)

What would be the best way to do this? I have considered simply using two
tables of strings, and use the byte read from the volt-ADC/amp-ADC as
indexes. The tables would be about 1500 bytes each..

3. Okay, one more: The design I was planning to use for the powersupply
(http://home.maine.rr.com/randylinscott/apr20.htm) seems very simple. (I
would use two identical, separate circuits) It uses a 5K potmeter to adjust
voltage. What sort of component could I use in place of the potmeter, so
that I could control it from the PIC?

Thank you!
Ole Petter

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