GAINING HIGHER ACCURACY

Creating a high-accuracy instrument is an interdisciplinary task. One nice area of improvement involves the reference voltage fed into the ADC. The Raspberry Pi Pico board doesn’t enables us to harness the entire capabilities of the RP2040 microcontroller. A detailed explanation of the issues faced can be found in section 4.3 of the Raspberry Pi Pico datasheet document.

Should you feel like improving your reference voltage, please avoid falling victim to the accuracy fallacy. The reference voltage doesn’t necessarily need to be precise: in the end, no one cares if the absolute value is 3.205V or 3.235V. Instead, absolute stability is important – keep in mind that components are affected both by ambient temperature and aging.

If you have a stable voltage reference at an odd voltage level, values can be massaged using various algorithms. Compensating temperature or aging effects, on the other hand, isn’t possible due to entropy. The same is valid for a resistor: if the voltage divider is constant with a ratio of 1:2.201, computing values isn’t an issue.

Incidentally, voltage reference design is one area where each multimeter vendor cooks their own soup. Datron, Hewlett Packard and Schlumberger Solartron take their own approach to the problem, the service manuals of the high-end products make for highly recommended reading. Finally, don’t forget mathematical processes. Using sophisticated filters lets you “eke out“additional information from imperfect hardware. Grouping together ten samples into one measurement, for example, eliminates some noise sources.