[time-nuts] uC ADC resolution (was: Poor man's oven)

[Poul-Henning Kamp]

--------
In message <3897C09A-D76C-474C-8907-9EA25F8C3451 at n1k.org>, Bob kb8tq writes:

>The “limited range” part of it is why the op-amp makes so much
>sense. If the ADC can “see” +/-10C that’s way more than will ever be useful.

Most uC's have a pile of mux'ed ADC inputs, so do all of the above:

AI0 = Full range

AI1 = +/- 10C

AI2 = +/- 2C

A big upside to this is that you will not need to invent heuristics
for clamped inputs in your PI(D) controller, something which is a bit
harder than most people realize.

Assuming a 10-bit ADC, the code will look something like this:

	double
	get_temp(void)
	{

		T = read_AI2();
		if (T > 50 && T < 975) {
			T += T2_offset;
			T *= T2_scale;
			return (T);
		}
		T = read_AI1();
		if (T > 50 && T < 975) {
			T += T1_offset;
			T *= T1_scale;
			return (T);
		}
		T = read_AI0();
		if (T > 50 && T < 975) {
			T += T0_offset;
			T *= T0_scale;
			return (T);
		}
		abort("You have problems...");
	}

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