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RP2040 ADC calibration (schematic)
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<blockquote data-quote="epsi1on" data-source="post: 739932"><p>I was working with raspberry pi pico ADC pins, and found out there are minor error in pico ADC (12bit) values:</p><p></p><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><p></p><p>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:</p><p></p><p><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></p><p></p><p>with above values ([ICODE]14[/ICODE] and [ICODE]4083[/ICODE]) it can be calculated that:</p><p></p><ul> <li data-xf-list-type="ul">Ru=291*RI</li> <li data-xf-list-type="ul">Rd=339*RI</li> </ul><p></p><p>so i've gone one step further and used a 100k 1/4w resistor:</p><p></p><p><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></p><p></p><p>then</p><p></p><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><p></p><p>with 1, the RI is calulated 5185 Ohm with 2, the RI is calulated 15762 Ohm</p><p></p><p>values 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?</p><p></p><p>Thanks</p></blockquote><p></p>
[QUOTE="epsi1on, post: 739932"] I was working with raspberry pi pico ADC pins, and found out there are minor error in pico ADC (12bit) values: [LIST] [*]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] [*]When ADC pin is connected to [ICODE]AGND[/ICODE], the readout value is [ICODE]14[/ICODE] but i expect [ICODE]0[/ICODE] [/LIST] 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: [URL='https://i.sstatic.net/ytNiu60w.png'][IMG alt="enter image description here"]https://i.sstatic.net/ytNiu60w.png[/IMG][/URL] with above values ([ICODE]14[/ICODE] and [ICODE]4083[/ICODE]) it can be calculated that: [LIST] [*]Ru=291*RI [*]Rd=339*RI [/LIST] so i've gone one step further and used a 100k 1/4w resistor: [URL='https://i.sstatic.net/kEK2cXeb.png'][IMG alt="enter image description here"]https://i.sstatic.net/kEK2cXeb.png[/IMG][/URL] then [LIST] [*]1- When input is connected to [ICODE]ADV_VREF[/ICODE], the readout value is [ICODE]3881[/ICODE] [*]2- When input is connected to [ICODE]AGND[/ICODE], the readout value is [ICODE]97[/ICODE] [/LIST] with 1, the RI is calulated 5185 Ohm with 2, the RI is calulated 15762 Ohm values 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 [/QUOTE]
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RP2040 ADC calibration (schematic)
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