Xduin - Yet Another Arduino Variant

Found myself again in a situation where I need just a couple of more I/O
and mega is kinda overkill. Trying to learn KiCAD too.
Didn’t take long to reduce it to this.

I want an arduino with:

  • Stuff you can buy and solder easily.
  • Schematics and PCB on OSS. (KiCAD, GIT)
  • MORE I/O

Features/Issues (Comparing to UNO)!

40 Pin ATMEL
0.5mm tracks
5mm wider board
Single Side Board

Up to 64Kb*
+10 Digital Outputs (6 PWM)
+2 ADC Inputs

FTDI Cable Connectors


  1. Separate 3.3v regulator for AVCC, good idea?
  2. AREF circuit.

Suggestions/corrections appreciated!!

Some eye candy:

3v3 regulator yes

single diode protection eh, on my protoboard arduino I used a full wave voltage rectifier, its not that much bigger and not that much more expensive and it does not care if you plug DC transformers in "backwards" or low voltage AC transformers (with smoothing capacitors in mind) , and of course since I did it, I will push it ;)

also I don't see a power switch, you don't know how stupid convenient that really is, and you have board space for both

Hi Osgeld, thanks for the comments.

Yea, will look for a 3v3 reg. Know any non-smd cheap/common? Found the LM1117.

Liked the full wave stuff, is your schematics available?

Power switch! haha, yea, good idea. I even solder a switch on my arduino USB cable, really helps, heh...

no I do not have a cheap n easy source for 3v3 on hand

full wave, eh radio shack for mine (though it cost a couple bucks parts houses will have it much cheaper) you have 2 (~) ac inputs and there is a + and a - output

its really 4 diodes looped together but at package size and cost its just better to get a premade one, and if you dont expect AC you do not have to change much, if you do you just need to add some "fat" caps to smooth over the transition, if you feed it DC it does not matter which connection is which on the power supply, its always right on the other end (so as long as its within spec of the regulator voltage your good, no matter how the plug is mis-wired, or in my application screw terminals cause dc jacks tend to be used up a ton and generally suck to fiddle with)


and yea even a basic jumper to cut on or off power is always overlooked (and jumpers are cool too cause you can hook up to a multimeter to measure amps)

Cool, got and implemented it.

Found a through hole 3v3 reg too: LP2950

How do you program the chip?, I can't see a way of doing it.

Hey jabber,

Yea, it's another to do. Thinking about a pin header for a FTDI cable. And another for rs232? (Didn't get to this part of the datasheet yet heh)

The idea is to leave connectivity as an addon. You choose, cable2serial, ethernet/wifi shield. Those shields usually use a lot of pins (wishield at least), so the extra dig outputs will come in handy...

yea you could do it like a bare bones or really bare bones, they have a 5 pin header

and then you have options of how you want to do it, I use one of their RS232 level converters, or its laid out for a ftdi cable or use whatever

Finished connections, auto-reset, fixed tx/rx place as pin 0/1.

But found a fun-blocker: Pins 13..8 on the arduino maps to bus PBx, PB0 -> 8 til PB5 -> 13. And those are the pins used in eth/wifi shields.

But on the DIP40, PBx bus is on the right , and PDx bus on the left. So I'll use PDx bus for pins 12..8 (Jumper for pin 13, not sure if the internal resistor is hardwired or bootloader)

Any idea if it'll work? If a patch to the shield lib make it work or it's really a problem....

Yup, nothing that some illustrations on a datasheet couldn’t elucidate.
PBx bus is wired to the SPI…
So, + jumpers to keep single side and arduino compatible…

Some links in my Atmega32/arduino section:



Why did you rule out adding a i2c ADC and i2c pcf8574a digital i/o expander?

I've taken to pcf8574a, I put my lcd on one, and some other i/o things I had, I freed up 7 pins on my 328.

The downside is that it takes more sw to accomplish, thats true.

Hi orbitalair, thanks for you comment.

Gonna read the sheet of that component later, but it's an expensive one.. Will try the 74HC595 for a led bar I've got here, not good for yr project?

But on the topic, yea there are plenty of ways to "create more I/O", but my goal is to understand a lil better the MCUs. I'm working in a Atmega328 version too, almost done..single sided but not serial, cheap and cool (it's on the repo as duin) heh.

Are you going to move the silk screen along the bottom pins? The numbers seem to be on top of the holes.