The featured picture is by OpenClipart-Vectors on Pixabay.
Building one’s own MCU board, one often does not use a crystal or resonator. Instead, the internal RC-oscillator is employed, which can be quite inaccurate. Similarly, if one wants to use the internal reference voltage to measure the supply voltage, it turns out that the reference voltage can deviate from its nominal value quite a lot. Both, the RC-oscillator and the internal reference voltage can be calibrated, though. In this blog post, I describe a simple method to calibrate both using only a UNO board and a multimeter employing the avrCalibrate library.