Arduino Pro Mini + MMA7361

Hi,

I need to use an accelerometer MMA7361 with an arduino pro mini 5V.

All the information that I could to find on the web are related in how to connect it to an arduino uno.

My main concern is about how set up the AREF to 3.3V. I couldn't find no useful information about it.

How can I do it ?

Thanks in advance.

Kleyson Rios.

Do you have to ? When you have the default 5V as reference, that isn't so bad ? is it ?

You can connect the AREF to the 3.3V pin, and select : analogReference ( EXTERNAL ) ; But you must be careful not to call analogRead() before the external reference is set, or else there is a shortcut between the reference voltages inside the chip.

Peter_n: Do you have to ?

Yes, I do. For accuracy.

Peter_n: You can connect the AREF to the 3.3V pin

That's the problem, there are no AREF neither 3.3V pins in the Arduino Pro Mini.

You are right, I didn't think of that :-[

Is your MMA7361 module with a voltage regulator ? Perhaps there is a 3.3V output pin ? On some modules, the 5V is the input for the voltage regulator and the 3.3V pin is the ouput of the voltage regulator. Do you have a link to your MMA7361 module ? or a photo ?

I think the 3.3V to AREF might be a few percentage more accurate. You could buy a digital accelerator sensor for more accuracy.

Hi Peter_n,

I'm using a mma7361 module like this one http://eecs.oregonstate.edu/education/docs/accelerometer/MMA7361_module.pdf

What's the options to set its reference to 3.3v using the mini pro ?

Can you just use the 3.3V version of the pro mini so AREF will be 3.3V? The module you linked to has both 5V & 3.3V input so it will power from the VCC pin of the 3.3V mini (into the 3.3V module input).

A 3.3V Pro Mini as Riva wrote is good, but I still prefer a digital accelerometer :stuck_out_tongue:

When 5V is applied to the module, the 3.3V pin of the module is an output. You can connect that to AREF. You have to know what you are doing, because connecting a voltage to AREF could cause a shortcut inside the microcontroller.

@Riva, to use a 3.3V version is also an option.

@Peter, where did you get this information ?

Peter_n: When 5V is applied to the module, the 3.3V pin of the module is an output.

And I've found this thread (http://forum.arduino.cc/index.php?topic=63294.0) where is said:

Peter_n: External A-Ref is pin 20, connects to Pin1 of capacitor C1, it is not brought out to an external pin. You can carefully tack a wire on it & bring it out.

So, I could use a 78L33 to reduce from 5V to 3.3V and connect it at Pin1 of capacitor C1 to set my external reference. What do you two think about that ?

Sorry for being so slow :confused: The Pro Mini does not have a 3.3V output, but also not a AREF pin.
I ment the 3.3V pin of the MMA7361 module, but since the Pro Mini doesn’t have AREF pin, you can’t use it.

The MMA7361 module has a voltage regulator of 3.3V. The 5V pin is the input and the 3.3V pin is the output of that voltage regulator on the MMA7361 module.

It is possible to find that capacitor on the Pro Mini board and solder a wire to AREF.

Short answer, yes! Aref IS available on a pro mini (& clone). Desolder C1 and solder a wire to the side indicated. Did it on my clone, works as expexted.

|500x287

I had the same problem. I've solved it by blobbing solder on pins 20 and 19, which connects Aref to ADC6. ADC6 is usually pinned out on later Pro Minis so it makes for easier access than a soldering to a capacitor.

In addition, there are several layouts of Pro Mini. On some, there's an obvious connection to a capacitor. On others it's not obvious and may not exist.