Arduino - ADC voltage measurement using Aref

 

 

- 아두이노 우노의 3.3V 핀을 A0에 연결해서 전압측정함.

>측정시 5V의 실제 전압은 4.65V가 나와서 (PC USB PORT <-> UNO) 이 값으로 Aref 핀에 연결하고 측정함. 

(이렇게 해야 정확한 값이 측정됨)

16:18:42.132 -> digital value = 742, Aref:4.64, ADC voltage = 3.36 16:18:43.188 -> digital value = 743, Aref:4.64, ADC voltage = 3.36 16:18:44.242 -> digital value = 740, Aref:4.65, ADC voltage = 3.36 16:18:45.312 -> digital value = 742, Aref:4.64, ADC voltage = 3.36 16:18:46.352 -> digital value = 743, Aref:4.64, ADC voltage = 3.36 16:18:47.423 -> digital value = 742, Aref:4.62, ADC voltage = 3.35 16:18:48.480 -> digital value = 742, Aref:4.64, ADC voltage = 3.36

 

- Aref 전압을 입력받아서 정확한 값 측정,

int sensorPin = A0;  // input pin for the potentiometer int digitalValue = 0;// variable to store the value coming from the sensor void setup() {   Serial.begin(9600);   // 아날로그 입력 핀을 읽기 전에 아날로그 기준 값을 외부 전원을   // 사용하는 것으로 설정합니다: } void loop() { //  analogReference(EXTERNAL);     delay(10);   digitalValue = analogRead(sensorPin);// read the value from the analog channel   Serial.print("digital value = ");   Serial.print(digitalValue);        //print digital value on serial monitor   float voltage = readAref();   Serial.print(", Aref:");   Serial.print(voltage);       float ADC_voltage = voltage * (float)digitalValue / (float)1024;   Serial.print(", ADC voltage = ");   Serial.println( ADC_voltage );        //print digital value on serial monitor   delay(1000); } // // Function readAref // // Reads AREF (when external voltage is supplied). // When the AREF pin is open, a value of 1.1V is returned. // This function is only valid for a voltage at AREF of 1.1 to 5V. // // The calculations can be translated for integers to prevent // use of float. // Only for the Arduino Uno, Nano, Pro Micro at this moment. // Experimental, no guarantees. // public domain // // Ref: https://forum.arduino.cc/t/is-there-a-way-to-print-aref-value/258646/9 float readAref (void) {   float volt; #if defined (__AVR_ATmega8__) #elif defined (__AVR_ATmega168__) #elif defined (__AVR_ATmega168A__) #elif defined (__AVR_ATmega168P__) #elif defined (__AVR_ATmega328__) #elif defined (__AVR_ATmega328P__)   // set reference to AREF, and mux to read the internal 1.1V   // REFS1 = 0, REFS0 = 0, MUX3..0 = 1110   ADMUX = _BV(MUX3) | _BV(MUX2) | _BV(MUX1);     // Enable the ADC   ADCSRA |= _BV(ADEN);   // Wait for voltage to become stable after changing the mux.   delay(20);   // Start ADC   ADCSRA |= _BV(ADSC);   // wait for the ADC to finish   while (bit_is_set(ADCSRA,ADSC));   // Read the ADC result   // The 16-bit ADC register is 'ADC' or 'ADCW'   unsigned int raw = ADCW;   // Calculate the Aref.   volt = 1.1 / (float) raw * 1024.0; #elif defined (__AVR_ATmega32U4__) #elif defined (__AVR_ATmega1280__) || defined (__AVR_ATmega2560__) #endif   // Try to return to normal.   analogReference(EXTERNAL);   analogRead(A0);            // the mux is set, throw away ADC value   delay(20);                 // wait for voltages to become stable   return volt; }