Measuring supply voltage of AVR chips via software @MicrochipMakes
MCUVoltage measures the voltage supply (Vcc) of Arduino without extra components. Supported board includes Uno, Leonardo, Mega as well as the ATtiny3224/3226/3227. This library also supports oversampling and averaging. Hardware oversampling for the ATtiny3224/3226/3227 is also supported.
While the Vcc is often assumed to be 5V for the Arduino, it is often not the case. Due to factors like having diode on the power rail, long USB cable, inaccurate bus voltage etc., Vcc can vary, usually between 4.5 to 5.25V.
Since analogRead() uses the Vcc as a reference by default, it may be useful to know the actual Vcc instead of making an assumption that it is 5V.
While the out-of-the-box measurement using this library may not be better than the 5V assumption, this library allows for calibration of the Vcc reading, and is able to achieve consistent results across various USB power supplies. Sadly, needs to be done on a board by board basis. An example, Calibrate_Bandgap is included to help with this calibration along with a digital multimeter.
This library is also useful for battery powered projects to read the current battery voltage, assuming it is hooked up directly to the Arduino.
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