Battery voltage checking

// Function created to obtain chip's actual Vcc voltage value, using internal bandgap reference
// This demonstrates ability to read processors Vcc voltage and the ability to maintain A/D calibration with changing Vcc
// Now works for 168/328 and mega boards.
// Thanks to "Coding Badly" for direct register control for A/D mux
// 1/9/10 "retrolefty"

int battVolts;   // made global for wider avaliblity throughout a sketch if needed, example a low voltage alarm, etc

void setup(void)
    Serial.print("volts X 100");
    Serial.println( "\r\n\r\n" );

void loop(void)
    battVolts=getBandgap();  //Determins what actual Vcc is, (X 100), based on known bandgap voltage
    Serial.print("Battery Vcc volts =  ");
    Serial.print("Analog pin 0 voltage = ");
    Serial.println(map(analogRead(0), 0, 1023, 0, battVolts));

int getBandgap(void) // Returns actual value of Vcc (x 100)
#if defined(__AVR_ATmega1280__) || defined(__AVR_ATmega2560__)
    // For mega boards
    const long InternalReferenceVoltage = 1115L;  // Adjust this value to your boards specific internal BG voltage x1000
    // REFS1 REFS0          --> 0 1, AVcc internal ref. -Selects AVcc reference
    // MUX4 MUX3 MUX2 MUX1 MUX0  --> 11110 1.1V (VBG)         -Selects channel 30, bandgap voltage, to measure
    ADMUX = (0<<REFS1) | (1<<REFS0) | (0<<ADLAR)| (0<<MUX5) | (1<<MUX4) | (1<<MUX3) | (1<<MUX2) | (1<<MUX1) | (0<<MUX0);
    // For 168/328 boards
    const long InternalReferenceVoltage = 1056L;  // Adjust this value to your boards specific internal BG voltage x1000
    // REFS1 REFS0          --> 0 1, AVcc internal ref. -Selects AVcc external reference
    // MUX3 MUX2 MUX1 MUX0  --> 1110 1.1V (VBG)         -Selects channel 14, bandgap voltage, to measure
    ADMUX = (0<<REFS1) | (1<<REFS0) | (0<<ADLAR) | (1<<MUX3) | (1<<MUX2) | (1<<MUX1) | (0<<MUX0);
    delay(50);  // Let mux settle a little to get a more stable A/D conversion
    // Start a conversion
    ADCSRA |= _BV( ADSC );
    // Wait for it to complete
    while( ( (ADCSRA & (1<<ADSC)) != 0 ) );
    // Scale the value
    int results = (((InternalReferenceVoltage * 1023L) / ADC) + 5L) / 10L; // calculates for straight line value
    return results;

Could you please format your code as following:

In which you replace:

// This #include statement was automatically added by the Spark IDE.
# include "WebServer.h"

By your code.
This formats your code in a way that makes it infinitely more readable, and would be greatly appreciated!

The code is for arduino not for spark core device

took it from here,92074.0.html

I’m aware of that, but by putting (any) code between those “```cpp” tags, it formats the code, so it’s a lot easier to be read on the forum. If you could edit your original post and try it, I’m sure you’ll agree on the difference :wink:
(wrong signs, use the ones in the picture above! They should be the ` signs)

It won’t change anything in the code, but makes is so much easier to read, and therefor debug/port/edit, for those trying to read it. Thanks in advance!

Got it . fixed .
Still the idea is i dont want to debug the code because this wont work on spark … i just uploaded it as exemple so you understand what kind of function i needed.
one that can read board voltage.


Hi @Gentmat

I fixed your code posting above in the way that @Moors7 suggested (thanks!). You can go back and edit posts for this sort of thing–click on the little pencil.

Unfortunately the STM032 chip on the Spark core does not have a bandgap reference so this type of self-measurement is not easy on the Spark core. You could add an external band-gap reference like the LM185/285/385 series and use the internal ADC or you could add a battery voltage IC like these: