Arduino mini pro 328p 16Mhz Voltage

[andymag]

Hi guys,

I am currently building a small device that is to be powered by a 3.7V battery and is run by an Arduino mini pro 328p 16Mhz microcontroller board. This board is to be powered by a 5V power supply according to the specifications. So I would need to add a step up converter, although I would like to avoid it.

Today, out of curiosity I tried to power the board (with only an oled display attached) by an adjustable DC power supply. At 3.0 Volts it seemed to work fine and drew only 20 mA. I incremented a number from 0 to 1000 without delay() in the code and it was done counting in one minute, which is the same time as it needed powered by USB.

Does anyone have experienced with powering 328p 16Mhz with only about 3V? I would love to avoid building in a step up converter but not sure how it behaves in some complex applications.

Any help is appreciated. Thanks a lot in advance.

Andy

 

[berkeman]

What do the datasheets for all of the components on the PCBA specify? Is the 5V input only used because it's a handy USB voltage? Is there a 5V to 3.3V step-down converter right after that 5V input? Do you have the schematic for the Arduino board?

 

[Wrichik Basu]

The specs page for Arduino pro mini says that they had two boards, one at 3.3V, and another at 5V. If you have the 5V board, it appears that they want it to be powered at 5-12V. However, there should be an option for BOD in the Arduino IDE. You can lower that value and then experiment a bit on whether the board will work at a lower voltage. For example, on a Uno or Mega board, the BOD can be set to as low as 2.7V.

@berkeman The schematics are available on the linked page, if you would like to give them a look.

 

[berkeman]

@berkeman The schematics are available on the linked page, if you would like to give them a look.

Thanks Wrichik; I'll have a look later today. What's BOD?

 

[andymag]

What do the datasheets for all of the components on the PCBA specify? Is the 5V input only used because it's a handy USB voltage? Is there a 5V to 3.3V step-down converter right after that 5V input? Do you have the schematic for the Arduino board?

Hi berkeman, thanks for the fast reply. There is a Linear Voltage Regulator. However, it regulates down only to 5V: https://www.lcsc.com/product-detail..._Microchip-Tech-MIC5205-5-0YM5-TR_C70431.html.

There are two versions of pro mini: 3.3V and 5V. I definitely have the 5V version.

On the other hand, I do not see any obvious component on the board that would require 5V. Some LEDs, a bunch of capacitors and resistors. shotky diode and a ceramic resonator. The IC seems to accept a wide range of input voltage: https://www.lcsc.com/product-detail...SOCs_Microchip-Tech-ATMEGA328P-AU_C14877.html

Below are the official arduino schematics and a third party BOM:

I am really wondering why Arduino would produce two different versions.

 

[berkeman]

Does the documentation say anything about SJ1 (the output jumper for the regulator)? It looks like the circuit runs on 3.3V but the regulator just lets you bring in whatever higher voltage is convenient for you. You may be able to remove SJ1 and power Vcc with your 3.3V supply. What range will your "3.7V" battery range over from full charge to low battery?

 

[andymag]

The specs page for Arduino pro mini says that they had two boards, one at 3.3V, and another at 5V. If you have the 5V board, it appears that they want it to be powered at 5-12V. However, there should be an option for BOD in the Arduino IDE. You can lower that value and then experiment a bit on whether the board will work at a lower voltage. For example, on a Uno or Mega board, the BOD can be set to as low as 2.7V.

@berkeman The schematics are available on the linked page, if you would like to give them a look.

Hi W. Basu, thanks. However, as I said it works with 3.0Volts. I just would like to understand if it is reliable. There must be a reason why they made different versions of the board. Maybe earlier the ICs from atmega were different and did not accept a range of voltages.

 

[andymag]

Does the documentation say anything about SJ1 (the output jumper for the regulator)? It looks like the circuit runs on 3.3V but the regulator just lets you bring in whatever higher voltage is convenient for you. You may be able to remove SJ1 and power Vcc with your 3.3V supply. What range will your "3.7V" battery range over from full charge to low battery?

unfortunately, there is no info regarding SJ1. At least, I have found nothing.

 

[Wrichik Basu]

What's BOD?

Brown-Out Detection.

 

[pbuk]

I am currently building a small device that is to be powered by a 3.7V battery and is run by an Arduino mini pro 328p 16Mhz microcontroller board.

There are two versions of pro mini: 3.3V and 5V. I definitely have the 5V version.

Er, why? Can't you just buy a 3.3V board?

 

[Wrichik Basu]

Er, why? Can't you just buy a 3.3V board?

The pro mini board is outdated and no longer produced. The alternative would be to use Nano, or maybe directly program an ATmega chip using another Arduino board via the Arduino as ISP protocol (which is what I do to reduce costs).

 

[Rive]

According to datasheet, the uC itself can run with anything from 2.7V to 5.5V, so I guess it's the environment what makes the difference between a 3.3 or 5V board: LEDs, attached devices and such.

If you can properly keep in mind that you have 3.3 instead of the 5V as VCC then I think it should be just fine.

 

[JT Smith]

The datasheet for the processor includes this graph for the safe maximum clock frequency for a given supply voltage:

It works out to a minimum safe voltage of 3.78V at 16MHz. You can get away with operating outside the safe zone but, you know, maybe sometimes it won't work depending on the particular part or maybe the temperature or who knows.

 

[JT Smith]

unfortunately, there is no info regarding SJ1. At least, I have found nothing.

That's there so you can power directly (e.g. with a battery) to VCC instead of RAW. That way you don't incur the power loss from the probably inefficient voltage regulator. Usually for low power you'd choose something less than 5V and instead of a 16MHz crystal you'd use the processor's internal 8MHz oscillator.

But if you really need 16MHz then to be safe you'll have to add a step up regulator. Pololu sells some pretty tiny and inexpensive ones. In that case you would also want to cut SJ1 to leave the unneeded onboard regulator out of the picture.

At some point it's easier to just make your own PCB. It isn't that hard to hand solder one of those processors.