/*
  *DC_voltage_measure_demo*

  Arduino DC Voltage Demo 1
  dc-voltage-demo.ino
  Use Arduino A/D converter to measure voltage
  Use external voltage divider with 30k & 7.5k resistors
  Results displayed on Serial Monitor
 
  DroneBot Workshop 2021
  https://dronebotworkshop.com

  Sketch takes voltage input and through a voltage divider
  feeds input to ADC pin. This value is calculated and returns
  a reading that is the original voltage in value.

  Using 3.3V aref, 
  ADC 1024 = 16.484V
  ADC 383 = 6.171V


*/
 
// Define analog input
#define ANALOG_IN_PIN A0
 
// Floats for ADC voltage & Input voltage
float adc_voltage = 0.0;
float in_voltage = 0.0;
 
// Floats for resistor values in divider (in ohms)
float R1 = 30000.0;
float R2 = 7500.0; 
 
// Float for Reference Voltage
// float ref_voltage = 5.0; // measured from 5V output of Arduino
float ref_voltage = 3.3; // measured from 3.3V output of Arduino

// Integer for ADC value
int adc_value = 0;
 
void setup() {
  Serial.begin(9600);
  Serial.println("DC Voltage Test");

  // Use 3.3 external voltage reference. 3.3 output to AREF pin.
  analogReference(EXTERNAL);
}
 
void loop(){
   // Read the Analog Input
   adc_value = analogRead(ANALOG_IN_PIN);
   
   // Determine voltage at ADC input
   adc_voltage  = (adc_value * ref_voltage) / 1024.0; 
   
   // Calculate voltage at divider input
   in_voltage = adc_voltage / (R2/(R1+R2)); 
   
   // Print results to Serial Monitor to 2 decimal places
  Serial.print("ADC Value: "); Serial.print(adc_value);
  Serial.print(" * Ref Voltage: "); Serial.print(ref_voltage);
  Serial.print(" / 1024 = ADC Voltage: "); Serial.println(adc_voltage, 3);
  Serial.print("ADC Voltage: / "); Serial.print(R2/(R1+R2));
  Serial.print(" = Input Voltage: "); Serial.println(in_voltage, 3);
  Serial.println("");
  
  // Short delay
  delay(3000);
}