Yes the internal reference voltage.
I've been having a look on the data sheet.
You are right, it establishes a gap in between the two values. It sounds a little bit strange, as the reference should be much more stable than a +- 10%. I wonder if it refers to the values you can expect for different batchs, being much more stable for a certain chip . . .
Perhaps it would be a good idea opening a thread on this concern.
Regards
olof_n:
I also read that the internal 1.1V reference actually can vary between 1.0-1.2V so a good external voltage reference should improve the accuracy even more when calculating the VCC.
Across all AVR processors ever made. Any given processor has a stable reference voltage that is between 1.0 and 1.2 volts.
vffgaston:
...the reference should be much more stable than a +- 10%.
It is. I have been testing a processor for about a month. I am getting a variance in the third decimal (1.116 to 1.120) over the entire voltage range (5.0 to 1.8) at room temperature (22 to 28). Which is a variance of about 0.36%. Certainly close enough for government work.
In the past I have gotten very similar results with various AVR processors.
I wonder if it refers to the values you can expect for different batchs, being much more stable for a certain chip . . .
Correct.
With a "external voltage reference" I thought about using a external voltage reference source like TL431 or better.
/Olof
With a "external voltage reference" I thought about using a external voltage reference source like TL431 or better.
/Olof
I'm a little bit confused: if accuracy is a must in your project then using calibrated resistors is much more important than the, small, error that can come from the arduino internal reference. As Coding Badly said, once measured (and introduced in your code or calibration menu option) the internal reference should be good enough.
I think. :.
Regards
I agree that that calibrated resistors are important, and if the internal reference are as good as Code Badly writes it won't be a problem.
I guess the 1.0-1.2V figures come from the wide operational range (-40°C to 85°C) a AVR processor has.
As I wrote above , accuracy is not a problem in my current project, it is more a discussion for future projects.
In my previous post I was just explaining what I meant when I wrote about "external voltage reference" (and a programmable voltage reference like TL431 certainly has its usage - it all depends on the project).
vffgaston, one more question. What should I search for if I want to buy low temperature dependant resistors? Are all 0.1% resistors "low temperature dependant"? Any special type of resistor?
Regards
Olof
I guess the 1.0-1.2V figures come from the wide operational range (-40°C to 85°C) a AVR processor has.
No: this is the point: the chip you have (in your project; mounted in your board) has a (very stable) voltage reference. It is not going to move depending on the temperature.
vffgaston, one more question. What should I search for if I want to buy low temperature dependant resistors? Are all 0.1% resistors "low temperature dependant"? Any special type of resistor?
Let me have a look. Post you a link.
Regards
Thanks again!
can you post correct with resistor for measure 0V to 60V
olof_n:
Thanks again guys for your help!
Now it works perfectly.First I followed Boardburner2 advice and changed the resistors to a lower value. The measurments was good up to ~52V.
I then understod that the zener had started to conduct as JohnLincoln mentioned and I removed the zener.
After that the measurments was good up to 60V .
I only print the voltage to my LCD with one decimal and it shows exactly the same voltage as my multimeter and bench power supply./Olof
CAN YOU PLEASE POST YOUR RESISTER COMBINATION !. ME TOO STUCK LIKE YOU AND CANNOT FIND THE SOLUTION FOR MY PROBLEM . I USE THE FOLLOWING RESISTER COMBINATION.
R1=220000;
R2=16400; (8k4 x 2 )
ADC REF UN TOUCHED ( DEFAULT 5V)
with this voltage divider I can measure up to 73V . IF TEST 5V USB AND 12V BATTERY SUPPLY IT SHOWS CORRECT VALUE . BUT WHEN I FIX WITH MY BATTERY IT SHOW 62V. I TRIED DIFFERENT COMBINATION, ANY ONE PLEASE HELP . I MEASURE WITH MULTI METER IT SHOW 54.6V.
Hi Anbudroid!
Unfortunately I have forgot the value, it was a long time ago.
The PCB is covered with glue so I cannot measure the value.
Do you know the exact AREF voltage? It is important.
If AREF is connected to VCC you can measure it with this code: Measure VCC
You can also try to add a trimpot to the voltage divider for calibrating.
/Olof
olof_n:
Hi Anbudroid!Unfortunately I have forgot the value, it was a long time ago.
The PCB is covered with glue so I cannot measure the value.Do you know the exact AREF voltage? It is important.
If AREF is connected to VCC you can measure it with this code: Measure VCCYou can also try to add a trimpot to the voltage divider for calibrating.
/Olof
Actually I said " I CAN MEASURE LOWER VOLTAGE 5 , 12" if I Use TrimPot Lower Voltage Change to 4.3V instead of 5 . I use LM2596HV Board For my power supply and I can surely said REF is 5V. also I can measure with adcVolt * 5 /1023 = 5v . any other solution now I choose r1=147K r2=10k. but Still Same .