Adc value to LCD using Arduino

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saugat

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I am trying to step down 40V dc supply using voltage divider circuit to 5 volts proportionally and the output voltage is to displayed on 16X2 lcd. I am always getting 0.0 on lcd, though i think my program is perfect.
I tried a lot but can not figure out what is the error in this circuit.
Please help me out.
Thanks in advance..
Here is my circuit



And here is my arduino code:

Code: 
#include<LiquidCrystal.h>
LiquidCrystal lcd(12,11,5,4,3,2);
void setup()
{
// set up the LCD's number of columns and rows:
lcd.begin(16, 2);
lcd.print("ADC value");
}
void loop()
{
  lcd.setCursor(0,1);
  float value = analogRead(A0)*5.0/1024.0;
  lcd.print(value);
}
 
Last edited by a moderator:

did you connect 40VBattery Ground(-ve terminal) to arduino ground?
 

I've never used an Arduino and I can't read the MCU type in your diagram but I suspect you are not following it's manufacturers guidelines about the impedance at the ADC input. Possibly the board also has a resistor to ground/supply on it as well which would effectively be in parallel with your series resistor chain.

Most MCU require an input impedance of < 10K to give accurate results. The solution is to use a buffer amplifier to provide more output current to the ADC input.

Another thought: does the "lcd.print()" function accept floating point numbers as input or do you have to convert to text first?

Brian.
 

yep, AVRs common ADC has a recommended input impedance of no more than 10Kohm... that voltage divider seems a little to high...
 

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