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# The explanation made sense. The board is taking longer.
- URL: https://sreekars-journal.labvion.com/pq-03-the-adc-explanation-made-sense-then-i-saw-the-pins/
- Published: 2025-06-11T12:30:00.000Z
- Updated: 2026-10-29T08:13:30.000Z
- Description: GAIN_ONE is a small name with a large effect on the meaning of a reading. The saved raw sampler selects it and gives the scale as 0.125 millivolts per count. It then reads A0 and A1 separately and calls computeVolts for each. I can follow that much directly instead of leaving the ADC as a box l
- Author: Sreekar
- Tags: Power meter, #Import 2026-10-29 10:08

GAIN\_ONE is a small name with a large effect on the meaning of a reading. The saved raw sampler selects it and gives the scale as 0.125 millivolts per count. It then reads A0 and A1 separately and calls computeVolts for each. I can follow that much directly instead of leaving the ADC as a box labelled sixteen bits. The conversion has a configuration behind it, and the number coming out is still the voltage at the ADC input. Sensor scaling is another step.

I'm trying to keep three different questions apart. What can the chip do? What does the small board around the chip provide? And how is this particular project using it? An explanation of the chip doesn't automatically explain every label on a breakout board. A drawing of one board doesn't automatically match another. If I move between them without checking, I can end up with a collection of individually sensible instructions that don't describe the same circuit. That’s a much more confusing problem than simply not knowing a term.

The number of bits was one of the first things that caught my attention. Sixteen bits sounds impressive. It describes the number of codes available, but it doesn't promise that every final reading will be accurate to the last displayed digit. The input signal, the chosen range, noise and the conversion into the original quantity still matter. I can have many possible digital values and still interpret them incorrectly. I'm finding that quite a few specifications answer a precise question while my first reading of them answers a much larger one.

The gain setting is another place where I need the actual configuration beside the explanation. It affects the full-scale range used for the conversion. That means the same raw count can represent a different input voltage under a different setting. I can't safely take a formula from one example and assume the program has selected the range that formula expects. Before worrying about the original voltage or current being measured, I have to know what voltage the ADC thinks its own input represents.

For one check, a conversion used steps of 0.125 millivolts. A change of 100 counts would then correspond to 12.5 millivolts at the input. If I change the step size, the calculation changes. It helps me see why the raw number needs its configuration with it. A count isn't a complete measurement any more than a length without its unit is a complete answer.

The same file prints raw counts and input volts side by side. That’s a useful pairing because I can check the arithmetic without pretending it already represents the original mains voltage or current. A count change and a voltage change should agree under the selected scale. The source also fixes the communication pins at GPIO 8 and GPIO 9 and begins the ADC at 0x48\. These settings belong to different questions, but they meet in one program: finding the device makes a reading possible, and knowing its conversion scale makes that reading interpretable.

There’s also a speed question waiting behind the range question. A changing signal keeps changing while the ADC is working. More possible values do not automatically mean more readings per second. I want to understand both, because a detailed answer taken at the wrong moments can still leave out the part of the signal I needed.

The address belongs to a different part of the problem. It lets the controller communicate with the device on I²C. Finding an address is useful, but it doesn't tell me the input range, the value on a channel or whether the sensor conversion is correct. I'm trying not to make one success carry more meaning than it has. There’s still something satisfying about that first communication target, though. It’s a small enough question that I can recognise an answer instead of wondering whether the entire meter works.

I'm also learning to look at the pin I'm reading about. It sounds obvious, but I can spend a surprising amount of time following an explanation on a screen without being able to locate the corresponding connection on the board. The name in the notes, the label in a drawing and the physical pin need to meet somewhere. Keeping them together makes the reading slower. It also tells me much sooner when I have understood the general idea but lost the actual arrangement.

The chip specification becomes much less abstract when it reaches a particular call and a particular unit. I can explain that part before asking the later equations to do anything with the result.