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Topic: New tutorial - the AREF pin (Read 7642 times) previous topic - next topic

tronixstuff

Have updated the AREF tutorial. It's pretty self-explanatory:

http://tronixstuff.com/2013/12/12/arduino-tutorials-chapter-22-aref-pin/
Check out my Arduino tutorials at http://tronixstuff.com/tutorials - Order my  Arduino book from http://nostarch.com/arduino

retrolefty

Nice write up. You might consider adding that the internal voltage references available are stated as nominal values. That is the 1.1vdc voltage reference may be between 1.0 and 1.2 for any specific chip. It will a stable reference but may not be exactly 1.1vcd and thus may not return the the reading one would expect if one always assumed that the 1.1vdc band gap is exactly 1.1vdc.

For that matter when using the ADC with the normal chip's Vcc (Avcc actually) one shouldn't expect the reference voltage to be exactly 5.000 vdc as USB voltage can vary from 4.75 to 5.25 or so, and the on board +5vdc voltage regulator will have some accuracy tolerance/variation.

A key to getting the best accuracy possible out of the arduino analog inputs is to be able to measure the actual Vcc and or internal voltage references so one can 'calibrate' the results in your mapping functions, if best accuracy is required.




mmcp42

on a UNO, you need to use
analogReference(INTERNAL), instead of INTERNAL1V1
:)
there are only 10 types of people
them that understands binary
and them that doesn't

polymorph

I find it distressing that they ignored Atmel's recommendation of an RC decoupling network when bringing Vcc to the AVcc pin. AVcc is the power supply to the ADC converter chip, not to be confused with Aref. Both should have bypass capacitors directly from the pin to ground to reduce noise in the ADC circuits.

The Freeduino has an empty spot to insert an 0603 chip capacitor for bypass on the AVcc pin, but no space for a series resistor as suggested by Atmel.
Steve Greenfield AE7HD
Nick Gammon on multitasking Arduinos:
http://gammon.com.au/blink
http://gammon.com.au/serial
http://gammon.com.au/interrupts

polymorph

Oh, and I wanted to say: Nice!

http://tronixstuff.com/2013/07/02/tutorial-arduino-and-the-ti-ads1110-16-bit-adc/

Also, if you want to know what the internal reference voltage actually is, you can measure it. When you have selected the internal reference (and I think you must do at least one analogRead), then you can just put a DMM on the Aref pin.
Steve Greenfield AE7HD
Nick Gammon on multitasking Arduinos:
http://gammon.com.au/blink
http://gammon.com.au/serial
http://gammon.com.au/interrupts

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