MrDEB,
You truly go to great lengths to avoid actually understanding how anything actually works. You must put forth considerable effort to avoid having any knowledge rub off on you, no matter how many times it's explained.
As for the floating input?? not sure if I need to worry about it since it is an ADC input
Why worry about a floating input? You are depending an an ADC reading to tell you what switch is read. When you tested it above, it was reading mid scale with no switch pressed because it's floating. That will wander around depending on electrical noise, humidity and the phase of the moon, so how will you know what's noise and what's a button press?
I planned on using the divide by 1024. 5 ? 1024 = .0048828
Aside from your error in math, why would you convert ADC readings into "volts"? You don't actually know what voltage a reading of 1023 means since you don't have a voltage reference. What you know is that ratio of the reading to the full scale value. A reading of 1023 means it's the same voltage as the supply voltage. Is it 5? 4.5? 3? Who cares. The steps from the switches will be the ratio from full scale, no matter what full scale is. Of course you haven't considered that if you convert some value to 2.345 volts, in integer math, that equals 2. You'll get only 4 or 5 steps using integer math...and 12 more pages in the forum trying to explain why.
actual circuit is IMO better than just doing the math. No guessing but just hard facts on the actual output.
No. Sorry. Your opinion is worth ZERO in this case. If you do this, you will have data for that exact set of resistors under those exact conditions. You mentioned using 1% resistors. The values of these resistors will vary by +/- 1%. No two resistor ladders made with 1% resistors will be the same. But it's easy to find the band each switch can be in. Use the voltage divider equation. Calculate the bound with all the resistors on the top of the voltage divider at the max value and all the resistors on the bottom at their minimum value. Then to the reverse to calculate the other bound. If your resistors are truly 1% tolerance, the ADC values MUST be within those bounds.
I'll bet I can design a circuit board to do this task, send the files to China, have the boards back, assembled and programmed before this forum thread reaches a conclusion.