I might be blind, stupid or barking up the wrong tree, but I can't find any information in here regarding how a pot's value affects the function of the ADCs. I know that PICs have a prescaler to customize linearity and such, but I'm having a hard time getting the ADC on a PICAXE to work exactly how I want it to. Perhaps I'm over-thinking it, I dunno. Can anybody render the straight scoop on this?
Back to basics; the POT(entiometer) is simply a variable resistor with a "slider" that can travel across the value of the POT; said value can be any value! Now, "any value" can become problematic because of the basic E=IR equation; which is to say, we wish to have voltage control via wiper rotation, but we do not wish to introduce significant current through the POT. Therefore, rule of thumb is often 10K - BUT, it can be 5K, 20K or 50K; at some high value point the ADC input current flowing in the PICAXE pin begins to distort the fact that we typically discard input pin current and that current would have an effect of the E=IR math; no longer being a simple, singular resistance.
POTs have an current limitation before heat (and ultimately cremation) become a concern: check out
http://sound.westhost.com/pots.htm
I strongly recommend that you spend a weebit of time with this free online program:
http://www.falstad.com/circuit/
You can create a simple POT voltage divider and then plot the voltage/current on a realtime graph. Using a real POT of the same value as the virtual POT and a high-impedance voltmeter, the simulation and the realworld results should match closely. Remember, POTs are not all linear, so ensure you have a linear POT by setting the wiper at 50% of rotation and ensuring you have 1/2 of the total resistance between either end of the POT and the wiper of the POT.
Here is the SPICE for the above:
$ 1 5.0E-6 10.20027730826997 50 5.0 50
174 320 352 384 96 0 1000.0 0.5 Resistance
v 240 352 240 96 0 0 40.0 5.0 0.0 0.0 0.5
w 240 96 320 96 0
w 240 352 320 352 0
O 320 96 432 96 1
O 384 224 432 224 1
O 320 352 432 352 1
o 5 64 0 34 5.0 9.765625E-5 0 -1
I also prefer to scale in software because we wish to keep the external E=IR relationship as stable as possible; the POT should be on a voltage regulated bus... +5V or whatever is feeding the PICAXE - definitely not an external voltage rail unless you are very, very confident with designing electronic circuitry and can ensure that the ADC input never exceeds the PICAXE positive supply rail- assuming a 0V ground reference.
If you require all 255 values for the 8-bit conversion, then no problem, use the value directly. However, sometimes an analysis of the need leads to a stepped-value requirement, and you can use Select Case to implement discrete actions for ranges of POT values.
Good luck.