Revised Hobbyduino Mini (Minimalist Arduino Clone)
June 25, 2011
A little while ago ignoblegnome (IG) did a review for me on my version of a minimalist Arduino clone designed to be used for prototyping and finished projects. The board design allows the Hobbyduino Mini to be used on a breadboard by soldering pin headers to the I/O sockets or in a finished project by attaching wires. IG also passed along some great suggestions for future versions. I took the suggestions he made and modified the original design. Below is the 3rd revision of the Hobbyduino Mini. Oh yeah, I also wanted to mention that I soldered these boards using my DIY Reflow Oven (I'm still getting the documentation together but the boards look really good \0/).
IG recommended that I change the location of the FTDI breakout labels as they were hidden under the right-angle pin header on the board. The FTDI labels on the revised board mirror that of the FTDI basic breakout board and the FTDI breakout cable from SparkFun. You'll notice that two of the pins are also labeled (GRN) and (BLK) to match the color coding of the FTDI breakout cable. This should eliminate any confusion on which way the breakout cable and/or the breakout board plugs into the FTDI header on the Hobbyduino.
IG also recommended that I move all of the digital pins to one side of the board, label the pins that also function as PWM, and breakout the RESET and AREF pins to separate headers. You can see the before and after below.
Each of the PWM pins are labeled with a tilde '~' just like on the UNO. The meaning of the tilde is described on the underside of the board for those that may be unfamiliar with the UNO.
There was a design flaw in the original board that did not affect operation but, could be a problem if you decided to run a board off of an external supply at the same time you were connected to the USB port on your computer through the FTDI connection. This is a no no as it has the potential to force current onto the USB port and possibly fry it. I did not have that happen but, it was something I should have caught in the original design. I fixed it by adding a jumper to allow the board to be powered from the USB port or external power. Now, the board can be connected to the USB port and powered externally without the worry of forcing current onto the port (provided you remember to set the jumper).
Lastly, IG suggested I reposition the positive and negative labels for the external power connector as the labels would be covered if a connector is soldered onto the board. I informed him that I caught that one and would fix it on the next design. See below:
You'll notice a 6-pin header just below the ATMega328 IC labeled as ISP. That connector will allow you to use the Hobbyduino with ATMega chips that do not have the Arduino bootloader installed by programming them with an external programmer such as the STK500 sold by SparkFun.
Finally, the board can be configured in a number of different ways to facilitate use. I soldered male headers and female headers onto the board in the pictures above. The female headers are the same that are used on the Arduino boards and shields to allow stacking. This decision will become more evident when I introduce the Hobbyduino Bootloader ISP shield. Ofcourse, the board could be configured with any combination of headers or none at all if it will be used in a finished project. IG also asked me why I went with a 28-pin ATMega328 dip IC instead of using its SMD variant and my response was to allow the IC to be easily removed from the board. There may be situations where you let the magic smoke out or simply want to wire the board up as an ISP to load the Arduino bootloader on other chips. I do intend to create a board with the SMD IC later on.
That's all for the Hobbyduino Mini V3.0. I'll introduce the Hobbyduino Bootloader ISP shield in another post.
Attached are the board files for this project. I can provide finished boards for those that are interested but, you are welcome to make your own. The boards were designed with the free ExpressPCB software.