I understood the basics of a voltage divider. The ratio between resistors is important. But between a 20K[ch937]/10K[ch937] voltage divider and a 2K[ch937]/1K[ch937] one, which one is the best ? I have to deal with a 80V power supplie. I have to. I have to use this power supplie to feed 2 things, 1 device that need this 80V, and the arduino UNO who needs between 7V and 12V according to arduino website. So, .... I am about to use a voltage divider, to lower the 80V, until 9V.
IF i use R1 = 2,53 K[ch937] and R2 = 20K[ch937], i have = Vout = R1/(R1+R2) * Vin Vout = 2530/(20000+2530) * 80 Vout = 8, 98 V
OK fine, but should i use R1 = 2,53 K[ch937] and R2 = 20K[ch937] or R1 = 25,3 K[ch937] and R2 = 200 K[ch937], or smaller, or bigger resistor ?
Should i use something to protect the Arduino ? from what , I don't know, maybe if the divider don't work very well or gives more that 9V in a brief time ... something like a voltage regulator ?