Arduino Mega Pro Mini

Hi all,
I have a project where I need a large number of IO pins, 10 Servos, bunch of LEDs and Input components to influence their behavior. Unfortunatly a Mega is size-wise too big. In my research I stumbled upon the Mega Pro Mini (or sometimes refered to as "Micro" or "Extra Mini", which I am assuming that these are all one and the same board).

To be honest, I have never heard of this board before now and there does not seem to be a lot of information about it (or rather the little information that I have found is not consistant). Has anyone used one in the past? and is it really comparable to a Mega only in a smaller size?

Thanks a lot for any insight.

Pixelworks

Please post a link to what you stumbled on. Won't the interconnecting wiring and any junctions you need be fairly big, even if the board is small? How are you planning to connect everything? For 10 servos, all 10 grounds and power connections have to go somewhere. You won't find that on board. Nor will the board power 10 servos directly.

Have you compared pins with the Mega? They are readable on the board.

How many LED's is "a bunch"? What "input components"?

Hi aarg,
thank you for your reply. My project is still in the draft phase, so it is not yet final how many LEDs, but somewhere between 10 and 20 I would estimate.

Just so I am not mistaken, I am not looking for help in programming the actual this or that. I would just like to know if there are any major differences between the Mega and the Mega Mini, that I need to take into consideration before I actually choose a board to begin with.

In that case, have you compared schematics? Because that is how the specific thing that you are asking about is done. Otherwise, you're just taking advice from strangers on the internet.

FYI there are limits on how much current individual and collective pins can source.

As of yet I am still looking for a schematic/data sheet for the Mini version.
Thanks for the reminder regarding the current restrictions, this I am aware of. I have done numerous Arduino projects in the past, just not with the Mega Pro Mini.

So, I'm not unfamiliar with the difficulty in obtaining schematics for these things. I do some scouting on the vendor sites, online generally. Often that will not produce results right away. Sometimes it involves combining sleuthing and Googling techniques, and doesn't always succeed. But I do have a collection of schematics of what you would think are undocumented devices, which I keep in my project folder. Sometimes all you can get is a fuzzy image that someone exported from a PDF. Come on guys!

But I've been curious about this board myself, so I'll have a look...

One way is to find out which outfit made it in the first place, be it Robotdyne, Sparkfun, whatever... often they have the original docs online. Like this:
https://robotdyn.com/pub/media/GR-00000185==MCUPROCAST-P0.05-ATmega2560-CH340C/Schematic==GR-00000185==MCUPROCAST-P0.05-ATmega2560-CH340C.pdf

:slight_smile:

Just for the servos and LEDs you do not necessarily need a mega, there are I2C servo driver boards, and LEDs are easily driven by an external chip (shift register, I2C expander, specific purpose LED driver chip, etc).

I've notices the smaller versions of the mega in the past, do not think there is much if any major differences except for the size.

Oh yes, I am a member of that club too. Searching and searching, often with conflicting results or what-have-you-not. :slight_smile: The confusing part is that (I think) some sellers have confused the Pro version with the Pro Mini... but as the Pro Mini was new to me up until about a couple hours ago I am not in a place to judge.

Thank you for the link, I actually just found that myself a couple minutes ago.

Robotdyn are one of the "good guys". Not only do they do original R&D and publish full specs, but the build quality is very high. I often pay the 30% or so more to get their boards vs. the clones.

Hi David,

Normally I would give you right, but this will be a demonstrator and in addition to all the servos and LEDs, there will be a large control panel with round about 20 input components (buttons, dials, even a joystick) that will allow the user to control each of the LEDs and each of the Servos.

That is good to know. I have not had the pleasure of dealing with Robotdyn yet, but that is most certainly a plus.

One thing I just noticed, though. The mini apparently doesn't have a USB serial interface chip. At least, looking at the images... so the link I posted is maybe for the other one...

Hi,
It looks by convention, if Mini is in the part name, it is less the USB chip.

Tom.. :smiley: :+1: :coffee: :australia:

Then maybe I did post the right schematic - depends on which one the OP really wants. Thing is, the online vendor listings aren't consistent about that. But most are calling the CH340 board the "Pro Embed".

The pro mini appears to lack the 3.3v regulator. I don't know how to link the schematic on this phone, but googling Robotdyn mega pro mini will get you to the product page which has the schematic.

< edit >
The link to the schematic: https://robotdyn.com/pub/media/0G-00005642==MEGA-PROMINI-ATmega2560/DOCS/Schematic==0G-00005642==MEGA-PROMINI-ATmega2560.pdf

You could look into this product, which is also a small Mega variant, without onboard USB to Serial.

http://www.inhaos.com/product_info.php?products_id=118

In the download section, you find the schematic and a support package for Arduino,
that allows usage of all the additional pins that are brought out on this module.

Hi Whandall,
Thank you for sharing. I could not find the board dimensions on the product page but I did find it on Ebay and there it is listed as "an Arduino Mega 2560 scaled down to 36.5x51.5mm". Which is slightly smaller as the Mega Pro Mini. I will have to compare the schematics of both boards, but size-wise this is certainly an option to consider for my project.

Yes, at least looking at the datasheets that I was able to find, that is my understanding as well. What helps matters even less, I have seen more than one seller offering a Pro Mini but having an article picture of a Pro (not a Pro Mini). Makes me wonder if they even know what they are selling. :confused:

@aarg Exactly, regarding the consistancy.

For my purposes, size and number of IO ports is important. As all options (Pro, Pro Mini, and the 2560 Core version) are all based on the same chip and have 54 IO Pins, all 3 are good. I may still need to connect an extender but all boards are compatible.
Size-wise, the Core version the smallest, then the Pro Mini and lastly the Pro, Nevertheless, all are within a couple mm of each other and therefore all 3 are "do-able".

I still need to compare the schematics, but I do not think there will be any major differences here either.

The data sheet

http://www.inhaos.com/downcount.php?download_id=144

gives the size of 36 x 51.2 for the module.

There are a couple of very similar boards I've seen around, most are based in CH340G serial adapters (more durable/reliable that the 16u2 used on official boards, but without the special features of that which hardly anyone uses). Robotdyn is one if the better chinese elecronic crap companies.

Those boards work fine unless you're doing something wierd that requires reprogramming the 16u2 to make it appear as some other USB device.

All an Arduino is is a microcontroller, a USB port, and a serial adapter (or for pro mini, just the 6-pin header), plus a linear regulator (ranging from "decorative" to "passable" in terms of current handling), connected together in the obvious way,and every other pin of the microcontroller brought out to header, and ideally with any needed bootloader preloaded onto the chip.

Personally I wouldn't use an atmega2560 for anything if I could avoid it (they had to make a couple of compromises that are kinda ugly to get that many pins, and break the 128k flash barrier, they cost a fortune even as bare chip despite being like a decade+ old.... You need pins, or flash? (generally, you want a part with not more than 128k of flash (at which point it needs a third byte for the program counter), unless you really need the flash, and not so many pins that they can't fit the pin registers in the low I/O space (Not surethe boundary on pre-2016 parts, on the modern ones it's 56, which is exactly reached by the highest-pincount devices available on the modern avr architecture._