Is there no internal Vref on Pro Mini Atmega 328p ?

Hello.

I’m starting to work with a Pro Mini from Deek_Robot but I’m noticing some difference from my usual Arduino Board Mega 2560.

On top of that, reading the Reference of the Pro Mini, it should be with a ATmega168. But instead, it’s a ATmega328p ???

I can’t find the Vref Pin ? Is there an internal Réfrence voltage on this ? 1.1V or 1.1V and 2.56V ? I guess, if there is, it’s not accessible from a pin like on a Mega 2560.

Then I have a Vin and a RAW. Where can I give it 5V and where can I give it 12V ? I guess the RAW is for 12 v
I want to work on car battery and I wonder if I can feed it up to 14.4V without damaging it ?

hary:
it should be with a ATmega168. But instead, it's a ATmega328p ???

Sounds like you got a "Pro Mini 328".

hary:
I can't find the Vref Pin ? Is there an internal Réfrence voltage on this ? 1.1V or 1.1V and 2.56V ? I guess, if there is, it's not accessible from a pin like on a Mega 2560.

You probably mean the "AREF" (Analog Reference) pin. The chip has one (pin 20) but it is not connected to any of the edge pins. It goes through a capacitor to ground.

hary:
Then I have a Vin and a RAW. Where can I give it 5V and where can I give it 12V ? I guess the RAW is for 12 v
I want to work on car battery and I wonder if I can feed it up to 14.4V without damaging it ?

The various VCC pins are for regulated 5V (or 3.3V if you have an 8 MHz model) and the RAW pin is for 7-12V. Using a higher voltage might cause the regulator to overheat. You could either use a 5V regulator and feed the board 5V through VCC or use a 7V regulator and feed the board 7V through RAW.

You probably mean the "AREF" (Analog Reference) pin. The chip has one (pin 20) but it is not connected to any of the edge pins. It goes through a capacitor to ground.

Yes you're right I meant AREF ! Ok so it's not accessible from the board.

Using a higher voltage might cause the regulator to overheat.

Well, i have some 12V regulator, so I might use these. It won't be energy efficient but...... I'll see later to get a better solution.

Thanks for your help.

hary:
Yes you're right I meant AREF ! Ok so it's not accessible from the board.

It's not brought out to an interface pin but if you need it you can solder a tiny wire to the pin or to the pin side of the capacitor.

Ok.

I don't really need AREF access all the time but I want to calibrate the 1.1V reference to make an accurate voltmeter.

When I know exactly the value of this reference, I can then use it in my code.
That's it.

Thanks for your support.

hary:
I don't really need AREF access all the time but I want to calibrate the 1.1V reference to make an accurate voltmeter.

OK. Just probe pin 20 (or 17 if it uses the 28-pin version) counting counter-clockwise from the notched corner. It may be easier to follow the trace from that pin to C1 and probe there.

My 328p chip is squared, it's not a 28pin DIP package.

and AREF seams to be located at pin 20.

By the way, how is it possible Atmel make a 32pin and a 28pin package when all the 32pin are used ?
The DIP package also has 2 GND, Vcc, AVcc.

And what difference do they make between Vcc and AVcc ?

Sorry for all these questions.

hary:
By the way, how is it possible Atmel make a 32pin and a 28pin package when all the 32pin are used ?
The DIP package also has 2 GND, Vcc, AVcc.

The 32-pin TQFP and MLF packages have A6 and A7 pins as well as one additional GND pin (three instead of two) and one additional VCC (two instead of one).

hary:
And what difference do they make between Vcc and AVcc ?

From the datasheet: "AVCC is the supply voltage pin for the A/D Converter, PC3:0, and ADC7:6. It should be externally connected to VCC, even if the ADC is not used. If the ADC is used, it should be connected to VCC through a low-pass filter. Note that PC6..4 use digital supply voltage, VCC."

The 32-pin TQFP and MLF packages have A6 and A7 pins

Do you mean ADC6 and ADC7 on pin 19 an 22 ?
What are these extra pin for ?

Note that PC6..4 use digital supply voltage, VCC.

You mean Vcc instead of AVcc.
I need to dig in more the datasheet indeed !
What area in the datasheet I could find explanation concerning this ?
Till now I though the uC had only 1 A/D converter !

hary:

The 32-pin TQFP and MLF packages have A6 and A7 pins

Do you mean ADC6 and ADC7 on pin 19 an 22 ?
What are these extra pin for ?

They are the 7th and 8th inputs to the ADC multiplexer... Two additional analog inputs.

hary:

Note that PC6..4 use digital supply voltage, VCC.

You mean Vcc instead of AVcc.
I need to dig in more the datasheet indeed !
What area in the datasheet I could find explanation concerning this ?
Till now I though the uC had only 1 A/D converter !

The chip has one A/D converter with an 8-input multiplexer.
The description of the Avcc pin was section 1.1.7 of the datasheet for the ATmega48PA/88PA/168PA/328P.

I think I see.
On this 32pin package they give us access to 2 more channel of the ADC, so we have A0:A3 (PC0:PC3) (I guess they can do analog/digitalWrite as analog/digitalRead with Pull_Up resistor) and also ADC7:6 that can do only ADC readings.
So, they're using only 6/8 channel of the ADC. And not 8/8 as you mean ?

Concerning AVcc, that's the pin that give the energy to the ADC to be able to work. It's not internaly wired as I thought.

I was mistaken with AVcc and AREF !

AREF can be either externally fed from 0 to Vcc or better AVcc, or internaly connected to internal refernce 1.1V or AVcc.

Thanks very much for helping and learning describing all the uC little trick !