Arduino analog input voltage

Hardware Arduino Yún
1

Hello! I'm a bit confused with the analog input voltage requirements for Arduino Yun. If I have 230AC voltage, I have to step down from AC 0-5V considering the positive and negative peak for the input requirements?
Reference: http://openenergymonitor.org/emon/buildingblocks/measuring-voltage-with-an-acac-power-adapter

From this, they use a AC-AC power adapter and then 2 resistors to step down. If I don't use the AC-AC power adapter but a transformer to directly step down the AC voltage, will it work? Sorry, I'm still unclear of this part.

2

Not 5.0 Volt, The Yun has hardware bug 5.0V is not stable (~4.5V) For correct results, using the 3.3v reference voltage as ARef instead of the messy 5V will be more precise and less noisy

http://forum.arduino.cc/index.php?topic=227839.msg2329395#msg2329395

If I don't use the AC-AC power adapter but a transformer to directly step down the AC voltage, will it work?

"AC-AC power adapter"="AC transformer"

The reason of use R1/R2 voltage divider is due to 1.16V AC transformer which is difficult obtained.

Change R1/R2 ratio to match with 3.3V.

3

Thanks for your reply!
If I don't include the capacitor and the two resistors 470K ohms R3 & R4, will it work?
My transformer steps down to 36.3 Vpeak to peak and I'm thinking of using one 10k ohms for R1 and maybe 110k or 120k ohms for R2. I will get 2.79 or 3.025 positive peak, do you think it will work?

4

lamela:
...
If I don't include the capacitor and the two resistors 470K ohms R3 & R4, will it work?
...

No.

lamela:
...
My transformer steps down to 36.3 Vpeak to peak and I'm thinking of using one 10k ohms for R1 and maybe 110k or 120k ohms for R2. I will get 2.79 or 3.025 positive peak, do you think it will work?

Yes.

5

What is the capacitor and the two 470K R3 & R4 for? I thought if I use one 10k R1 and 120k R2 to step down the voltage, it will meet the input requirement on the arduino?

6

lamela:
What is the capacitor and the two 470K R3 & R4 for? I thought if I use one 10k R1 and 120k R2 to step down the voltage, it will meet the input requirement on the arduino?

Shift signal level by 3.3V/2=1.65V, make signal level in Arduino accept arrange ( 0~3.3V). otherwise will be (-1.65V~+1.65V).