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Date: Thu, 5 Mar 2015 20:03:12 +0100
From: Gabriel Paubert <paubert AT iram DOT es>
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Subject: Re: [geda-user] [OT] Temperature sensor and control recommendation
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On Thu, Mar 05, 2015 at 11:00:30AM -0600, John Griessen wrote:
> On 03/05/2015 10:21 AM, DJ Delorie wrote:
> >I use the same averaging trick on my thermostats to get 0.1F readings
> >on a 1C-rated sensor.  If your sensor isn't noisy enough to use this
> >trick, you can always add noise - you're basically building a 1-bit
> >ADC.
> 
> The extra noise lets you explore the single bit crossings of your system statistically.
> Then you get out of the trap of temperature varying, but not seen crossing single bits
> of the system ADC.

That's called dithering and it's used on instruments like low frequency
spectrum analysers to increase dynamic range. I remember one HP spectrum
analyser from the time when these things were carefully documented,
adding some bandpass-limited noise around the Nyquist frequency of the sampler
but above the displayed frequency range (which was only a quarter of the
sampling frequency if I remember correctly).

But for very low frequencies, I would these days consider either a high
resolution delta-sigma ADC (LTC24xx for example but there are many
others), or a time proven solution like a VFC (voltage to frequency
converter). Monostable based VFC need a high stability capacitor to work
properly, but synchronous V/F (AD652, AD774x) do not need any critical
component, and with only two wires for the interface, are easy to
isolate galvanically or optically.

    Gabriel