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'[EE] clean A/D'
2002\10\07@190717 by Nick Stedman

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I would like to get the really clean A/D conversion, so would it be
recommended that I use shielded wire, like audio cable to hook up the
variable resistors/passive sensors to the ADC, or is noise not generally a
factor? And to be clear, the shield connects to VSS, right?
TIA
nick

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2002\10\08@142125 by Mike Singer

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> Alan B. Pearce wrote:
> With regard to the original problem of noise on the analogue
> signals, this is where you need to sort out a proper grounding
> scheme for your sensors. If the sensors have a metallic body,
> then you will need to ground these back to the central "ground
> point" at your processor. If the sensors do not have a metallic
> body then you may need to have some form of metallic shield
> around it to stop hum pickup from surrounding mains wiring.

Proper shielding & grounding are really needed, but if even
this doesn't help, I'd suggest we should transmit digital, not
analog signal.
As example, voltage to frequency converter could be used
close by sensor. Pulses should be counted by PIC's counter.
Counter values should be stored as a stream in RAM.
Then, to calculate input voltage you should find a difference
between last stored value and the value stored at of one or
few steps ago.
The approach is extremely noise-immune due to its integrating
nature.

Mike.

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