Two ways to determine the input resistance of any measuring device.
?Add series resistance to the input until measured voltage reads half what it did without the resistance.? This external resistance is then the same as the internal input resistance.
?Add a large series resistor (100K or greater) and measure voltage drop across this resistor while measuring a voltage near the maximum input.? Then calculate current through this added resistor and use that to derive input resistance for the meter from current and voltage at the meter input.
This gets tricky with some ADC devices because the charge capacitor in sample-and-hold
circuits causes different current flows based on left over charge from a previous hold action.
This is partially why in my code I read the ADC input twice and take the second reading as
On Thu, Sep 20, 2018 at 8:21 AM Jim Purvis <jimpurvis7474@...> wrote:
Arv interesting project. Do you know or can you tell me how to find out the input resistance of such a meter?? I don¡¯t seem to find it on the Arduino spec sheet.? When building an RF probe the series resistor is calculated based in meter input resistance.? Yes, not critical if all you need are relative readings or differential gain/loss measurements.? But would be nice to have the reading somewhat accurate.? Jim wa7hrg
