Frankenstien R0.1, that was more than 5 minutes ago, I forget what that was about
Per question 1,
puff wrote:Is that okay? Why is that so?
Sure why not
![Smile :)](./images/smilies/icon_e_smile.gif)
I'm assuming R250 = 36k, and R251 = 10k, as well R252 is also 10k.
I see it like the below, it appears to be fairly linear. I forget how it was skewing at the low end and top end for that chip. That was several years ago perhaps it skewed around 0.50V of either rail. From a quick eyeball, I believe you have not yet hit the skewing areas of the op-amp. I seem to recall the lower rail was the problem. We changed the resistor divider ratio to avoid the issues at the higher end, but 0V can not be scaled, so problems at the low end. To me it appears the ADC voltage just above 3% error, and consistent. Even with 1% resistor the tolerance stack up makes sense to me. I see the front end resistor divider being 1%, then the op-amp offset voltage, which is then again has 1% from the output divider.
![Capture.PNG](./download/file.php?id=2978&sid=ebf442ded7d22eba57f6d99dd4a96afd)
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puff wrote:Which value should I use for coefficient in tuner studio?
I do not know the TS constants. That would be an
@ question. Either that or provide it with a solid 12V or 14V voltage and adjust the constant until you read that voltage. If you eyeball it like this, you can calibrate out some of the resistor tolerances.
puff wrote:All the times 5V rail of the board was 4.97V
As 5V dip's, so does the op-amp voltage. If your high end skewing was at 0.05V from the top rail, then you drop this by an additional 0.03V, your top end voltage would skew at 0.08 from 5V. However at 14V you are only 3V, so you have allot of room before you start to skew. The analog is based on the 3V regulator, this regulator did not drop voltage because of this variation in 5V. So it would have read the same as it always does. AKA ratiometric issues do not apply in this situation. It's basically an absolute reading, and it will function until your 5V drops significantly more than you have noted.