Re: Gaussmeter - hall-effect sensors


"Melodolic" <a@xxx> wrote in message
news:O%klg.88276$wl.36954@xxxxxxxxxxxxxxxxxxxxxxxxxxxxx
My gaussmeter project is moving along. I dropped the multimeter idea and
I'm
doing one with a PIC. It reads the voltage from a hall-effect sensor
through
the ADC, crunches the numbers and puts a gauss value on a 4-digit display.
(The multimeter idea went for a burton last night, when my shiny new
16F876A
sprang into ADC life - I wasn't looking forward to doing deltaV * 320 in
my
head, outdoors, anyway!) I've migrated most of the bits, other than the
chip, from the PIC development board to a breadboard.

I'd like to use it to measure very small quantities - milligauss. Can I do
something to the sensor's output to amplify the voltage changes within a
small range, while still presenting 0-5Vdc to the PIC's ADC, with a null
around 2.5V? Per the earlier idea with the multimeter, I'd like to use the
same supply that runs the PIC and LEDs.

Can I do something like: apply a -2.5V DC offset, amplify the resultant,
apply a +2.5V offset, and send that to the ADC? (If my single-rail 5V
supply
precludes this, can it be done if that's disregarded?)

Do these sensors have the resolution to match a display that can show
9.999
gauss? If not, what's the best high sensitivity range I can hope for?
99.99?


--
Melodolic Spielberg

I don't believe you have enough bits in the PIC ADC's to do what you want.
These ADC's are 10 bits and if you use all 10 bits you have one part in 1024
as the maximum resolution. You are asking for one part in 10,000 which at
minimum would take 14 bits. In order to provide head room and less fooling
around with precise analog range, gain and offset, I'd go for a 16 bit ADC.
You can still use a PIC for linearization and display taking two bytes at a
time and processing as a 16 or 14 bit word.
Bob


.

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