Analog reference on Arduino MKR1000

Hi, is there any reason why the analog reference works on Arduino UNO and MEGA2560 but not on MKR1000?
I need to set the reference voltage to 1.5V on the Arduino MKR1000 but it seems not to work.

Thanks,
Corrado

CORRADO2016:
Hi, is there any reason why the analog reference works on Arduino UNO and MEGA2560 but not on MKR1000?

The processors used on the UNO and Mega2560 aren't even from the same manufacturer much less are they in any way similar chips to the one on the MKR. There's no reason to think that anything from UNO or Mega2560 is going to apply to MKR1000.

I understand but the question is why the MKR1000 has the AREF pin?
If it's there I suppose it can be used, right?

Is there any other way I can change the reference voltage on the MKR1000.
I chose this board because of the 12bit DAC and the small dimensions.
I need to read a load cell with high resolution and the only way I can reach this resolution is to reduce the reference voltage.

Thanks!

CORRADO2016:
I need to read a load cell with high resolution and the only way I can reach this resolution is to reduce the reference voltage.

Do you want to measure load cell voltage directly with the Arduino.
No instrumention amp. No excitation voltage regulator.
Bad idea.
Even a 12-bit A/D will have very few A/D values with the ~20mV or so output of a load cell.

Use a specialised breakout board for that, like the HX711 (ebay).
Excitation voltage regulator, instrumentation amp, PGA, and 24-bit A/D.
Can interface with any Arduino.
Leo..

No, I'm not connecting the load cell directly to Arduino: I'm using a load cell amplifier (Standalone Load Cell Amplifier [LCAMP] - 14.99GBP : Leo Bodnar, Simulator Electronics).

My load cell can read up to 3Kg but I need to read a max weight of 2 Kg with a resolution of 0.5 gr.

At 2 Kg I have a signal of 1.5V so I would like to set the reference voltage at 1.5V and with the 12 bit DAC of the MKR1000 (4.096 values) I should be able to have the resolution I need (2.000 gr/ 4.096 = 0.488 gr).

If I can't set the reference voltage to 1.5V I cannot have this resolution (if I?m not wrong, the default ref voltage is 3.3V so I have a resolutin of "only" 1 gr).

This solution is just for the prototype than I will go with a custom board (w/out Arduino).

If anyone has another (fast) solution please let me know.

Corrado

Sorry, forum is broke so I can't quote from iPhone.

You say the pin is there so you "suppose" it should work. Why suppose? Why guess? Go read the data sheet for that product and find out for sure.

I already did it (I searched also on the Internet) and I didn't find the answer and that's why I'm asking here in the forum to understand if anyone has succesfully used the AREF with EXTERNAL reference with the MKR1000.

My "suppose" means:

  • I'm using a board from Arduino family that can normally use the AREF
  • the AREF pin is on the board (why making it available if it cannot be used?)
  • the AnalogReference documentation says:

DEFAULT: the default analog reference of 5 volts (on 5V Arduino boards) or 3.3 volts (on 3.3V Arduino boards)
INTERNAL: an built-in reference, equal to 1.1 volts on the ATmega168 or ATmega328 and 2.56 volts on the ATmega8 (not available on the Arduino Mega)
INTERNAL1V1: a built-in 1.1V reference (Arduino Mega only)
INTERNAL2V56: a built-in 2.56V reference (Arduino Mega only)
EXTERNAL: the voltage applied to the AREF pin (0 to 5V only) is used as the reference.

as you can see in the last row there is no exclusion for the MKR1000 board (as in other cases)

so my "assumption" was the AREF should work.

Corrado

So you use a 5volt instrumentation amp on a 3.3volt MCU.
That means the output of the instrumentation amp must be dropped with a voltage divider to <3.3volt.
Or lower if you can use 1.1volt Aref. Don’t know.
This board seems badly documented, so shouldn’t be used IMHO.

That still leaves the question of how to get a stable excitation voltage.
Arduino’s 5volt rail is a poor choice.
Load cell output depends on load cell supply. And you have a fixed gain opamp.
You walk a narrow path with these parts. Better get a cheaper and better HX711 board.
Leo…

I will check for the HXT11.

@GrOnThOs: thanks for the link ... I watched it that's exactly what I need to do BUT the problem is still that I can't make the AREF pin of the MKR1000 work!

Sorry if I insist but, apart from some improvements on the load cell amp that I can certainly implement, the question is still if anyone is (succesfully) using the AREF pin on the MKR1000.

Thanks,

Delta_G:
The processors used on the UNO and Mega2560 aren’t even from the same manufacturer much less are they in any way similar chips to the one on the MKR. There’s no reason to think that anything from UNO or Mega2560 is going to apply to MKR1000.

Actually the processor on the MKR1000 is in fact manufactured by Atmel. Atmel ATSAMW25 SoC (System on Chip) to be exact. The MKR1000 even has a a product called the MKR2UNO in the store that basically gives you a 3.3 Super Uno with WiFi; https://store-usa.arduino.cc/collections/products-atheart/products/tsx00005

Anyways!!

I use the Aref pins on the MKR1000 and have never had a problem with them. I have also used them with the MKR2UNO and it works flawlessly.

For a quick help see; http://arduino.stackexchange.com/questions/31605/analog-reference-aref-pin-on-arduino-mkr1000-not-working