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### Topic: Uno Reference Voltage of 1.1v (Read 7462 times)previous topic - next topic

#### gggggggg

##### Jan 17, 2013, 12:31 am
Hello, I am told the Reference Voltage of 1.1v exists on the UNO, but can someone please tell me which pin I need to connect my multi meter to, to read it.

thanks

#1
##### Jan 17, 2013, 12:34 am

http://arduino.cc/forum/index.php/topic,38119.msg282514.html#msg282514

#### gggggggg

#2
##### Jan 17, 2013, 01:07 am

http://arduino.cc/forum/index.php/topic,38119.msg282514.html#msg282514

Perfect, thank you.  1.071v

#### gggggggg

#3
##### Jan 17, 2013, 03:51 am
Follow up question:  if my voltage is 1.071, and the system is expecting 1.1, does that mean I can hook up the Positive of my battery power source to A1, read the value, and get 97.36363636363636% of that value as the current voltage in my battery source?

Or would I need to get 102.7077497665733%  of it, to get the current battery source voltage.

2.7% is a fair amount to be out.  Aside from the above example, where else would you use a value like this?  I have a triply axis gyro/accel/temp in my project (connected to A4 and A5  - https://www.sparkfun.com/products/11028) does that mean I should expect my results there are 2.7% out also?

Or is it even more complex than that, and I have to apply the 2.7% to the current battery volt.  Check that against 5v (or 3.3v), and use that new ratio or 'something' against my values based on if my module is using 3.3v or 5v source from the arduino.

#### mauried

#4
##### Jan 17, 2013, 04:12 am
Its important to read the spec sheet for the Atmega328 when looking at the internal voltage referance specs.
The 1.1 volt referance can vary anywhere between 1.0 to 1.2 volts, which is 20% variation.
Its not a stabilised voltage referance.
If you want a stabilised referance voltage for things like calibrating voltmeters, then you need something like this.
Voltage guaranteed to be stable within 0.02%.
They aint cheap though.

#5
##### Jan 17, 2013, 04:20 am
Its not a stabilised voltage referance.

You are not reading the specifications correctly.  The variation is due to manufacturing differences.

#### retrolefty

#6
##### Jan 17, 2013, 04:23 am

Its important to read the spec sheet for the Atmega328 when looking at the internal voltage referance specs.
The 1.1 volt referance can vary anywhere between 1.0 to 1.2 volts, which is 20% variation.
Its not a stabilised voltage referance.
If you want a stabilised referance voltage for things like calibrating voltmeters, then you need something like this.
Voltage guaranteed to be stable within 0.02%.
They aint cheap though.

I'm not sure I can agree with you that the internal voltage reference is not a stabilized voltage reference. There can be device to device variation for the nominal 1.1vdc band-gap reference, but for any specific chip it will be a stable voltage reference that will be somewhere within that stated range. And once one does actually measure the specific bandgap voltage of their specific chip then steps can be developed a calibration factor one might apply to ADC readings.

Lefty

#7
##### Jan 17, 2013, 04:24 am
...hook up the Positive of my battery power source to A1, read the value, and get 97.36363636363636% of that value as the current voltage in my battery source?

Your "battery power source" has a voltage less than 1.071?

#### gggggggg

#8
##### Jan 17, 2013, 05:02 am

...hook up the Positive of my battery power source to A1, read the value, and get 97.36363636363636% of that value as the current voltage in my battery source?

Your "battery power source" has a voltage less than 1.071?

No my source is ~5v.   My reference voltage is 1.071v

#### mauried

#9
##### Jan 17, 2013, 05:07 am
The spec sheet is here.
http://www.atmel.com/Images/doc8161.pdf

Vint Internal Voltage Ref   Min 1.0 Typical 1.1 Max 1.2
Seems pretty clear to me.

#10
##### Jan 17, 2013, 06:08 am
The spec sheet is here. ... Seems pretty clear to me.

In that case you should have no problem explaining when the internal reference would be 1.0 volts and when it would be 1.2 volts.

#11
##### Jan 17, 2013, 06:15 am
No my source is ~5v.   My reference voltage is 1.071v

So you'll be using the technique described in that post?  Using the battery voltage as a reference to measure the 1.071V bandgap?

#### dhenry

#12
##### Jan 17, 2013, 01:39 pm
Quote
Vint Internal Voltage Ref   Min 1.0 Typical 1.1 Max 1.2

Not sure what those Atmel guys were thinking when they designed that sucker.

#### retrolefty

#13
##### Jan 17, 2013, 03:36 pm

Quote
Vint Internal Voltage Ref   Min 1.0 Typical 1.1 Max 1.2

Not sure what those Atmel guys were thinking when they designed that sucker.

Well to me that spec is giving the nominal band-gap voltage allowable range for any specific chip you might obtain, not the stablity spec of the band-gap voltage which is not specified in the datasheet. It's been my first hand observation that the band-gap voltage is very stable, just different nominal values for different chips.

Lefty

#### olf2012

#14
##### Jan 17, 2013, 06:47 pm

Quote
Vint Internal Voltage Ref   Min 1.0 Typical 1.1 Max 1.2

Not sure what those Atmel guys were thinking when they designed that sucker.

Well to me that spec is giving the nominal band-gap voltage allowable range for any specific chip you might obtain, not the stablity spec of the band-gap voltage which is not specified in the datasheet. It's been my first hand observation that the band-gap voltage is very stable, just different nominal values for different chips.

Lefty

It is specified, data sheet page 525, and it is "quite stable"

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