ADC input for arduino uno (0-5) volt. I want to measure 100 volt . Using voltage divider rule how much current need to flow to analog pin to get sense..
I used 100k and 5k resistor. But arduino uno can't sense the voltage..
Thanks
Find an on-line Ohms law calculator.
You add up your total resistance, using a voltage higher then what you are going to measure, enter these values into the ohms law calculator, and you'll get total current flow. From there you can figure the voltage drop at the resistor junction, you can use the Ohm's law calculator. The voltage drop, calculated, at the resistor junction should be less then 5V.
I will state that I have figured out that a 100K and a 10K resistor will allow the Arduino Uno to handle 55 volts. I use the 100K/10K for a max voltage of 35 volts; a safety. What I am also writing, is that you mention you used a 100K and a 5K resistor network. I'm not going to do the math for you but consider that a 100K/10K combo gives the Arduino Uno the ability to handle 55 volts. I figured you applied 100 volts to your less then adequate voltage divider and the reason your Arduino does not measure voltage any more is that the Arduino is, most likely, dead, now.
atiarali:
I used 100k and 5k resistor. But arduino uno can't sense the voltage..
That ratio should work, so you must have done something else wrong.
Read the "how to post" sticky, so we get all the information to help you.
Leo..
You're thinking about it wrong. The ADC should have a really high input impedance so forget current.
I've read that the ADC will sense up to 5V so you just need a simple voltage divider-
Use the formula: R2=Vout/((Vin-Vout)/R1)
Simplified: R2*R1/(Vin-Vout)
Vin - the 100V
Vout - the max voltage into the ADC when Vin is 100% (5V if supply to the arduino is NOT 3.3V | 3.3V if supply is 3.3V | 1.1V if you use the Internal Reference)
R1 - Pick a value (10K is good, you want enough current to overcome the ADC impedance).
IF R1 is 10K, it HAS TO BE AT LEAST a 1W resistor!
R2 - Unknown, solve for.
Vin
|
R1
|- Vout
R2
|
GND
100V Vin + 10K R1 = 526Ω R2 (for 5V Vout)
-OR-
R2=341Ω if supply is 3.3V
R2=111.2Ω if you use the 1.1V internal reference.
For 100volt-in you shouldn't choose a top resistor value less than 100k,
to keep fault current under 1mA in case you make a mistake.
I would use 1k to ground, and measure with 1.1volt Aref enabled.
Leo..
There's usually no reason not to use 10k for the lower resistor, since that's going to get full
precision for the least current draw.
For 100V use (100k+100k) : 10k.
These are common resistor values, and using a series string of resistors is a good idea with high
voltages around - no one component fault can destroy the Arduino.
Note that the levels of current involved (0.5mA) are safe for the Arduino should the lower resistor
fail. The upper resistor limits current and thus damage.
Using 10k : 500 divider will both blow up the Arduino should the 500 ohm resistor become detached,
and overheat the 10k resistor unless its rated at 1W or more.