RE: Arduino Analog Input scaling

JWx — Wed, 19 Mar 2025 10:20:35 GMT

according to the datasheet, internal voltage reference of RA4M1 is more like 1.4V than 1.5V

https://www.renesas.com/en/document/dst/ra4m1-group-datasheet p. 95

Internal reference voltage input channel (min, typ, max)
1.36 1.43 1.50 V

the same issue is when using Atmega328 (Vmin = 1V, Vtyp = 1.1V, Vmax=1.2V)

I have even built Arduino calibrator once to increase measurement precision when using internal reference...

maybe some external reference of known value is needed to avoid calibrating the code for given reference voltage of the given MCU?

RE: Arduino Analog Input scaling

kmikemoo — Wed, 19 Mar 2025 02:15:08 GMT

[mention:626e6e27c407492d81c7e989443cdd1c:e9ed411860ed4f2ba0265705b8793d05] So... span error based upon the expected voltage. I don't think you're measuring anything incorrectly. You are just experiencing compounding tolerances of components. IMHO. It sounds like your span error is consistent. You can correct the displayed reading with a minor correction factor in the Arduino code. It's the temperature version of you tuning your servos for your robots. If the span error is consistent between the two Arduinos, at least you know the culprit lies in the circuitry you are connecting - and it should remain consistent enough to use the same code in different microprocessors. If it is different when you go back to the Nano, it's internal to the Arduino and each microprocessor will need to be "tuned" for the sensing circuit.

Or I'm misunderstanding the problem completely. I wouldn't rule that out.