[Zappie]

Hi, 

Something i'm really missing is the possebillity to insert a calibrated external voltage reference. Very easy to add i think!

Regards, Zappie

Where you think that having it, will significantly improve the readings?

Where minivollts are readout from analog ports, The internal reference is stable, but still has about a +/- 10% error. To improve accuracy  of the analog readings i mostly use little calibrated voltage reference modules. They have almost the same size as the transmitter module.

Regards, Zappie

It's easy to theorize about some design options, with generic solutions: So, let's go...
Some of the analog reads done on the TX unit, use 1.1V internal reference, others use the 5V reference. How to use two external precision reference voltage sources without adding additional switching circuitry? Another consideration... if we chose to use just one reference voltage for the ADC, it must be 5V or at least 4.096V, but in that case we are seriously penalizing the resolution when we are reading those millivolt signals... talking on this: its right that the 1.1V Arduino internal reference voltage have a tolerance of around 10% from chip to chip, but it doesn't float, so in the worst case, on some chips it can be just 1.0V and on another it can be 1.2V. There lots of confusion about this matter, as most people think that the bandgap voltage floats on the same chip.

On both cases where we are using the 1.1V internal reference (Solar Radiation and UV sensors), both require additional hardware / software calibration after sensors installation, so having a reference voltage of 1.0V or 1.2V doesn't matter, since it doesn't change on the same chip.

...i mostly use little calibrated voltage reference modules. They have almost the same size as the transmitter module.

The use of the little MCP1541 chip, with its output connected to the Arduino AREF pin can be an easy way...


Regards

Thats how it is...but isn't it easiier to calibrate when you first calibrate your internal reference for the chip used at that time?
The module i'm using have the MCP1541.

Regards, Zappie