The OP may use 1023 but it really should be 1024 ;) And yes, you can only measure up to 1023 * (5/1024) = 4,995V, not 5V.
OP, you print mV but you just print the value in V. The change in value for a steady voltage is just because of the ADC error in de Arduino. The LSB is just flipping.
But, like I said many times around here, don't use floats. They are slow, inaccurate and not necessary.
I changed the code to not use floats. Also, 4 digits is "to much" for the 10-bit ADC in the Arduino. The reading isn't that accurate, every bit is almost 5mV. So I limited to 3 digits (but you can change it to 4 if you really really want).
/*
Read Analog Voltage
Reads an analog input voltage on pin A5 & common ground, converts it to voltage,
and prints the result to the Serial Monitor.
Attach the center pin of a potentiometer to pin A0, and the outside pins to +5V and ground.
Includes a Loop Command for future use
// Indicates Notes & Compiler Does Not Include
; Semi Colon After Each Command
Chad J. Stoltzmann 04-08-2015
*/
// The setup routine Runs once when you press Reset:
int Counter =0; //Simple Counter Loop (See Below to Close Loop)
void setup() { //Needed in all Code!
// Initialize serial communication at 9600 bits per second
Serial.begin(9600); //BAUD Rate
Serial.println("*****Upload to Micro-Controller Complete*****"); //Text
Serial.println("*****Reading Device Analog Voltage Input*****"); //Text
}
// The loop routine runs over and over again forever:
void loop() { //Needed in all Code
int sensorValue = analogRead(A5); // Read Input V on Analog Pin (A5) and Ground on UNO R.3
// Convert the Analog Reading (which goes from 0.00 - 1023) to a voltage (0.01 - 1V):
//Do multiplication first to keep accurate. Long because 1023 * 5000 is to big for an int.
unsigned long voltageInMv = sensorValue * 5000UL;
//check for rounding errors, if remainder is larger then halve the resolution, add 1 mV
if(voltageInMv % 1024 >= 512){
voltageInMv = voltageInMv / 1024 + 1;
}
else{
voltageInMv = voltageInMv / 1024 + 1;
}
Serial.println(Counter = Counter + 1); //Simple Counter Loop Adjust (1) with Integers
Serial.print(voltageInMv / 1000); //Print the whole volts
Serial.print("."); //Print decimal point on same line
Serial.println(voltageInMv % 1000); //Print decimal places (up to mV) and end line
Serial.println("Volts(mV)"); //Text
Serial.println("_________"); //Text
delay(1500); //Delay(ms)
}
