Output voltage if Atmega is running at 3.3v ?

[ahmedadelhosni]

Hi.

I guess it is a silly question but I recently knew that there are 3.3v arduino mini boards. I thought it is another atmega chip which operates using 3.3v rather than 5v. But after searching I found out that it is the same chip but one board has 16Mhz clock and flashed to operated by this clock at 5v, while the other has a bootloader to run on 8Mhz at 3.3v, Am I correct ?

Thus powering the atmega using 2x1.5 batteries is not a problem for me now. But what about the output voltage of the pins ? How much volt can I use ? Will the output voltage decrease while the battery is discharged ?

THanks.

[mfalkvidd]

Yes, you are correct.

If you are powering the Arduino through the RAW pin, pin voltage will be 3.3V as long as the battery voltage is above 3.35V. However, that's not the best way for battery-powered sensors because the voltage regulator will use power even if the Arduino is sleeping.

With 2xAA you power the Arduino usin the Vcc pin, and preferably remove the voltage regulator and the power led. In that case, pin voltage will be the same as the battery voltage. With BOD enabled (default), your arduino will continue to work as long as the battery voltage is above 2.8V

The data sheet for the ATmega328 will give you all the details on the voltage requirements at different frequencies. It can be made to work with even lower voltage, and the next limit is 1.9V which is the specified limit for the nrf radio module.

See http://www.mysensors.org/build/battery for lots of more information on battery powered sensors.

[ahmedadelhosni]

@mfalkvidd Thanks.
I read about arduino mini hacks to reduce power like you have said. Actually my questions where relating to voltage value after doings these steps.

You mentioned that the voltage will be 3.3v as long as the battery voltage is above 3.35v
But most projects uses 2x1.5v which is 3v with 8 Mhz or even less clock. you said that the atmega will continue working as BOD is enabled and battery voltage is above 2.8v. So does the Output pin is equal always the battery voltage or what does happen ? which is in that case 3v for example ?

[mfalkvidd]

Sorry for confusing you with the 3.35V stuff. Read this part again:

@mfalkvidd said:

In that case, pin voltage will be the same as the battery voltage.

[ahmedadelhosni]

@mfalkvidd Yeah right. It's nearly 1 AM and i didn't notice it
Thanks.

[mfalkvidd]

No problem, you're welcome