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[on:]

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
    * Headers for power inlet (+5V and GND)
    * Small enough to fit in a small plastic box




Any comment will be appreciated.

Jeonlab

[Reply #1 on:]

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.

[Reply #2 on:]

I don't see any caps for the crystal, or is that an oscilator?

A couple of mounting holes never go astray.

______
Rob

[Reply #3 on:]

Why not just get a Promini?

[Reply #4 on:]

Or a Teensy?

(too lazy to post a picture)

[Reply #5 on:]

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

[Reply #6 on:]

Where does the 1Mohm resistor go?

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.

[Reply #7 on:]

And its schematic. Similar to a promini really but without voltage regulator.

[Reply #8 on:]

I was playing with a atmega644 version also, for more IO & memory, a la ardweeny style, and as a promini style

[Reply #9 on:]

Thanks for all of your comments. 

@frank: I live on Clark between Dufferin and Bathurst.  So close!  I also thank you for the advice on the resistor.  That's good to know.

@graynomad: The resonator (ceramic) has 2 built-in capacitors.

@crossroads: Thank you for sharing your ideas as well.

I will update some more detail soon.

Thanks.

[Reply #10 on:]

http://www.varesano.net/blog/fabio/first-picture-femtoduino-smallest-lightest-arduino-compatible-board-ever

i like it, maybe you too....

Greetings Chris

[Reply #11 on:]

GND pin that is near RST pin. How would you plug this board to a proto-board?

[Reply #12 on:]

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.

[Reply #13 on:]

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.

[Reply #14 on:]

Where does the 1Mohm resistor go?

You don't need one, that's for building oscillators out of discrete CMOS logic gates where a DC feedback path is needed, the ATmega oscillator circuits are more sophisticated!