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Message: <blockquote data-quote="epsi1on" data-source="post: 739932">I was working with raspberry pi pico ADC pins, and found out there are minor error in pico ADC (12bit) values:<ul> <li data-xf-list-type="ul">When ADC pin is connected to [ICODE]ADV_VREF[/ICODE], the readout value is [ICODE]4083[/ICODE] (average of 100k samples) but i expect [ICODE]4095[/ICODE]</li> <li data-xf-list-type="ul">When ADC pin is connected to [ICODE]AGND[/ICODE], the readout value is [ICODE]14[/ICODE] but i expect [ICODE]0[/ICODE]</li> </ul>So i think there is need to calibration. To calibrate, i think there is need for a schematic. so i did my first try with the simplest schematic i could imagine, like this:<a href="https://i.sstatic.net/ytNiu60w.png"><img src="https://i.sstatic.net/ytNiu60w.png" alt="enter image description here" class="fr-fic fr-dii fr-draggable " style="" /></a>with above values ([ICODE]14[/ICODE] and [ICODE]4083[/ICODE]) it can be calculated that:<ul> <li data-xf-list-type="ul">Ru=291*RI</li> <li data-xf-list-type="ul">Rd=339*RI</li> </ul>so i've gone one step further and used a 100k 1/4w resistor:<a href="https://i.sstatic.net/kEK2cXeb.png"><img src="https://i.sstatic.net/kEK2cXeb.png" alt="enter image description here" class="fr-fic fr-dii fr-draggable " style="" /></a>then<ul> <li data-xf-list-type="ul">1- When input is connected to [ICODE]ADV_VREF[/ICODE], the readout value is [ICODE]3881[/ICODE]</li> <li data-xf-list-type="ul">2- When input is connected to [ICODE]AGND[/ICODE], the readout value is [ICODE]97[/ICODE]</li> </ul>with 1, the RI is calulated 5185 Ohm with 2, the RI is calulated 15762 Ohmvalues do not match so i think the schematic is not corrent! is there any better schematic that can describe the internals of RP2040 ADC pins?Thanks</blockquote>

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