I have thought about minimizing the Arduino board because what I found in many cases was that I didn’t need the FTDI USB interface once the sketch was loaded, and I thought the Arduino board is kind of ‘big’ for its contents.
So here is a summary of my concept of mini Arduino compatible board. Its name will be ‘JeonLab mini.’
28-pin DIP ATmega328P with Arduino bootloader
Digital pins from 2 to 13 are arranged on one side
Analog pins from 0 to 5 are arranged on the other side along with the FTDI-USB connector for an external FTDI breakout board
There is no reset switch, but header pins for RESET and GND are provided
A power LED and #13 LED
A 0.1uF capacitor for the auto-reset when uploading a sketch
Hey you live in Vaughan? I'm around Dufferin and Center.
What you want to do with your design other than to fit it into a box? I don't think you'd want to experiment with a board inside a box unless you cut a hole for headers and wires to come out, and if this board is meant for experimentation, it's missing a lot of features, I think a built in v-reg is an important one (what's the point of a pretty box if there's another power supply dangling outside of it), and why would you ever leave out a reset switch?
My philosophy for designing a prototyping platform is to add features that don't take away from usability, and do not care about the cost (to a point). So add a reset switch, ISP headers, add both 5V and 3.3V power supplies, and put a ferrite bead + capacitor on the AVCC.
Also DO NOT use a 330R resistor on the pin 13 LED, you'll screw up your SCK signal if you ever decide to use SPI, try 1 kohm instead.
I have played around with layouts also, here's a minimalist 328-based board, double sided with all connections on top and the bottom being all ground plane. I was experimenting with spare holes for other parts to see what would fit on a standard expressPCB board using all thru hole components.
With little, tiny, wires
You'd probably want to connect it to a row of header pins, plug the pins into the protoboard.
Then make a breakout cable that matched an FTDI-basic adapter or similar for programming it.
Maybe put male pins on each end instead.
GND pin that is near RST pin. How would you plug this board to a proto-board?
My initial idea was to use this board as a stand-alone with header pins or header female sockets. In other word, this board is not designed for using on a solderless breadboard. However, this board might be used on a breadboard if you have a multi-column breadboard. My board will cover all the holes in a standard single column breadboard which has only 5 holes (0.1" apart) on each side. Anyway, if you have a multi-column bread board and need to use it anyway, here is a way to use the reset and GND pins: attach pin-headers on each side except for the GND pin next to the RST (reset) pin. There is another GND pin (6th from the bottom) on the right hand side of the board for the FTDI connection and you can use it for the reset function.
Jeon seems to want to try making a board. Do it right and it'll be worth it. It's great to have a tool tailored to your own needs.
If you want cheap PCBs made, Itead Studio can get you 10 pieces for $28 + shipping, that's way cheaper than anything in North America or BatchPCB.
I don't see any caps for the crystal, or is that an oscilator?
Judging from his website, he prefers resonators
I think resonators are usually used with a 1 Mohm resistor
Actually, if you make it 5cmx5cm or smaller, you can get it for $12 for 10... according to their website. Have you used them before? Are they actually trustworthy? I've never heard of them, but it is a good deal. The cheapest us provider I've found was sparkfun's side company, which is $10 setup + $2.50 per inch, plus shipping, for 1 prototype. The site you mentioned is $16 including shipping (to middle US) for 10. Definetly a deal if you don't mind waiting the time. (DHL was around $25 for shipping, but they have a basic ground shipping for $4.00, so it's worth the wait for me.) Just wondering about them.
I used both the 5cm by 5cm and 10cm by 10cm services, I also own a MiniLogic from them, works like a charm! Itead Studio definitely has characteristic products that you won't find else where and his store definitely deserves more attention. There's unique products and cheap graphic LCDs.
SparkFun (aka BatchPCB) is actually slower, because they actually have to fill up a panel with multiple people's designs before sending it to the manufacture in China, where it takes a week to get made. And then it has to ship from China to SparkFun, and then SparkFun to you. The services offered by Seeed Studio and Itead Studio sends your designs right away and the manufacturer is obviously closer to them since they are already in China.
However I do have some criticisms about some of his products (some of which is just personal preference). I don't want to rant too much here about an unrelated topic though.
I do not think it's worth the effort to try squeezing a design into 5cm by 5cm, at least not this type of design. Also Jeon already has an enclosure that he's designing it for.
If you want small, the ATmega328P does not require any external hardware to run at all, just use the internal 8 MHz oscillator. You can literally glue on a button/coin battery to it and have it run code. This is why I think it's pointless to get it that small.