Let's Make Robots!

Arduino pro mini undershield

The cheapest Arduino clone on Ebay is probably the small Arduino pro mini clone. I've bought some pro minis on Ebay for less then 3$ a piece from a Chinese seller. It's a tiny board with an ATmega328 running @ 5V. It does not have an USB/serial chip, so you need your own USB to serial converter.

The boards I bought came without header pins soldered on them. But included were strips of male header pins. I do not find these boards very usuable in a project, robot... They are good to prototype on a breadboard but that's about it. I'm not a fan of breadboards. I prefer to connect the different electronic modules I use with wires with female dupont connectors. As this is easy, flexible and makes for a good connection.

So I thought about designing an "undershield" for these pro minis and started playing in Eagle. This is what I have come up with: The PCB has 4 rows of headers. First row is GND, second is 5V, third row is the connection to the pro mini. The fourth row is the female header in which the pro mini plugs in. For connecting a battery there is a small screw terminal. The pro mini is fed through the "raw" pin, it gets the battery voltage through a schottky diode. The male 5V headers pins are powered from a simple linear voltage regulator. I would use a LM2940-5, but a 7805 would also work if you feed it +7V.

What do you guys think about it? I haven't ordered any boards yet but I might sent of the design to China to have 10 made.

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When I first saw this post it grabbed my interest because over the last few months I have acquired a few (20) of these Arduino Pro Mini clones. Then I realized that you have a different version than the ones that I purchased. Mine have additional pins (A4,A5,A6 and A7) that are accessible through four through holes like the ones pictured in the Unix_guru post.

So I set out to make a similar design that would add these pins and use all SMD parts. Here is what I came up with http://letsmakerobots.com/node/40286.

Edit Note: I realized that it was wrong to post my design in Bajdi's blog. I removed most of the info and placed it in a new blog linked above. I apologise for the breach of etiquette!




All the Pro Mini's I have bought on Ebay came without a bootloader. So I first bootloaded them with my USBasp.

Do you buy them from gc_supermarket? Is it possible to check if there is a bootloader? The green led blink really slowly (about 10/15 seconds on and the same seconds off).

no real way to check for bootloader besides any delay in the sketch launching (the arduino bootloader takes about a second to run before it begins your code, this is for checking the DTR signal to trigger programming from the arduino IDE I think) but I doubt you would notice that delay if its 10/15 seconds on/off with a blinking sketch.

However it can't hurt to try oddbots guide to reflashing the bootloader.

Thanks 6677, I'll try

Hi, I haven't an usb/ttl converter. How can I program this arduino pro mini using  arduino 2009?

I tried to remove atmega328 from the arduino 2009 and to connect arduino pro mini in this way:

arduino pro mini                   arduino 2009

GND                                   GND

GND                                   GND

VCC                                   5V

RXD                                   TX

TXD                                    RX

DTR                                    RESET

then I set in the arduino ide the arduino type to "arduino pro or pro mini (5v 16Mhz)w/atmega328".

I connected arduino 2009 to pc via usb and set arduino serial port to "/dev/ttyUSB0".

When I press upload the green led(should be on 13 pin) blinks a bit but the bar stay at about 90% for 5 seconds.

Then the ide show me "avrdude: stk500_recv(): programmer is not responding" message error.

I tried to change che arduino model in the ide but with similar results, and I tried also without removing the arduino 2009 microcontroller.

On the arduino pro mini there is a red led always on (I think power led) and a green led( I think on 13 pin) wich blinks with a period of about 30 seconds(15 on and 15 off, I think it's a preloaded program)

How can I solve these problems?

I'll have a look if I can squeeze a FT232 chip in between the pins. But I don't get why you guys want USB onboard. It's much easier to buy a CP2102 breakout board from China, an FT232 chip costs about the same: http://www.electrodragon.com/product/cp2102-usb-ttl-uart-module-v2/ 

By this point, might as well just buy a Nano clone.   I get it...  :)


Exactly... I'd rather have it as small as possible with 3 pin headers for powering sensors, etc.

My homebuild ProMini boards are very handy IMHO, just takes a bit to solder them up, make power / ground traces, etc.


I'm using two of these pro minis in my current project...  Useful little critters. 

I agree with 6677 though that it would be nice to have the "ability" to solder on a USB/Serial if needed....