battery charger by reading the data sheet of the battery and copy the full charge battery voltage then make a little adjustment in the program code for
disconnecting power when the battery voltage, reach or you can make it as battery protection circuit for example cut the power when the battery reach 3.0v and so on.
Demonstration
connect the positive of the battery to 100k resistor and the ground of the battery to 10k resistor with the Arduino then connect the resistors between each other and put a wire from analog pin A0 of the Arduino to the resistors connections after that make the connections wire between the LCD and the Arduino board like the image below.
Arduino code
#include <LiquidCrystal.h>
//RS,E,DB4,DB5,DB6,DB7)
LiquidCrystal lcd(7, 8, 9, 10, 11, 12);
int analogInput = A0;
float vout = 0.0;
float vin = 0.0;
float R1 = 100000.0; // resistance of R1 (100K)
float R2 = 10000.0; // resistance of R2 (10K)
int value = 0;
void setup(){
pinMode(analogInput, INPUT);
lcd.begin(16, 2);
lcd.print("DC VOLTMETER");
}
void loop(){
// read the value at analog input
value = analogRead(analogInput);
vout = (value * 5.0) / 1024.0; // convert to 5v scale
vin = vout / (R2/(R1+R2)); //Equation to read the value between the resistors
if (vin<0.09) {
vin=0.0;//statement to quash undesired reading !
}
lcd.setCursor(0, 1);
lcd.print("INPUT V= ");
lcd.print(vin);
delay(500);
}
voltmeter 7segment
if you want to use 7segment instead of LCD 16x2 you need to use "SevSeg.h" library and the code also below.Install the 7segment library: SevSeg.h
Arduino code
#include "SevSeg.h"
int pot=A0;
float vout = 0.0;
float vin = 0.0;
float R1 = 100000.0; // resistance of R1 (100K)
float R2 = 10000.0; // resistance of R2 (10K)
int value = 0;
SevSeg sevseg;
void setup() {
byte numDigits = 3;// the number of digits
byte digitPins[] = {2, 3, 4 };// digit power pins
byte segmentPins[] = {6, 7, 8, 9, 10, 11, 12, 13};// connect from A to P
Serial.begin(9600);
sevseg.begin(COMMON_ANODE, numDigits, digitPins, segmentPins);
sevseg.setBrightness(90);
}
void loop()
{
// read the value at analog input
value = analogRead(pot);
vout = (value * 5.0) / 1024.0;
vin = vout / (R2/(R1+R2));
if (vin<0.09) {
vin=0.0;
}
sevseg.setNumber(vin,2);
sevseg.refreshDisplay();
Serial.println(vin);
}