3S Lipo battery monitor
Hi,
I’m tring to setup a lipo Battery monitor using an Arduino Nano and an I2C 128x64 Display OLED.
I have surf and found many example to do it, and I have implement this code :
#include <SPI.h>
#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64
#define OLED_RESET 4
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);
const int analogInput1 = A0;
const int analogInput2 = A1;
const int analogInput3 = A2;
const float R1 = 13.2; // (100K + 8.2K) / 8.2K
const float R2 = 13.2; // (100K + 8.2K) / 8.2K
const float R3 = 13.2; // (100K + 8.2K) / 8.2K
float readCellVoltage(int inputPin) {
float vCell = analogRead(inputPin);
if (vCell < 0.09) vCell = 0.0;
float returnValue = (vCell * 1.1) / 1024;
return returnValue;
}
void setup() {
analogReference(INTERNAL);
display.begin(SSD1306_SWITCHCAPVCC, 0x3C);
display.display();
display.clearDisplay();
display.setTextColor(WHITE);
display.setTextSize(1);
}
void displayLipoMeter() {
float B1Voltage = (readCellVoltage(analogInput1) * R1);
float B2Voltage = (readCellVoltage(analogInput2) * R2) - B1Voltage;
float B3Voltage = (readCellVoltage(analogInput3) * R3) - ( B1Voltage + B2Voltage );
display.clearDisplay();
display.setTextSize(2);
display.setCursor(0, 0);
display.println("LiPo Meter");
display.setTextSize(1);
display.setCursor(0, 12);
display.println("---------------------");
display.setCursor(0, 20);
display.println("- V Cells -- V LiPo -");
display.setCursor(0, 30);
display.println("Cel1= |");
display.setCursor(31, 30);
display.println(B1Voltage);
display.setCursor(0, 40);
display.println("Cel2= |");
display.setCursor(31, 40);
display.println(B2Voltage);
display.setCursor(0, 50);
display.println("Cel3= |");
display.setCursor(31, 50);
display.println(B3Voltage);
display.setCursor(65, 36);
display.setTextSize(2);
display.println(B1Voltage + B2Voltage + B3Voltage);
display.display();
delay(5000);
}
void loop() {
displayLipoMeter();
}
The code work but I have a problem that the read value is not stable, I mean the values have a window from 4.14V to 4.25V but for all the cells the voltage measured with a multi meter is 4.18V-4.19V.
I 'm became crazy with un-useful small code refinements or voltage divider value correction >:( , but nothing change the results. The values are still be from 4.14V to 4.25V 
.
Any suggestions?
