Here's 2 ATMega168's sharing one 16mHz resonator, one reset switch, two 10k resistors, one 220ohm resistor, and two LED pilots.

Both chips were supplied with RBBB kits sold by The Modern Device Company http://www.moderndevice.com/RBBB.shtml.

I used a mini USB adapter and uploaded the LED blink test to both chips, and as Paul suspected, they are perfectly synchronized - I've tested numerous resets, and the start up blink sequence and blink demo on both, are identical.

I don't need synchronized chips, but I happen to have a use for 2 168's connected via i2C - not sure if anyone else does but it adds a lot of pins and a second serial buffer for an almost next to nothing outlay. This can be put together using 1 RBBB and a second chip with the boot loader installed, so that's quite inexpensive, so long as you've got got a mini USB adapter laying around

The video can be viewed here (it's scratchy but you'll get the idea)

http://www.youtube.com/watch?v=eDu_SrhP5-M

Here's some pix too.

beavis wrote on 14.03.2008 at 14:10:01:


They've been running non stop for the past 4 days to see if anything "flaky" happens, the chips are cold to touch and both are in perfect synchronization.

I'm interested to know - why would a water cooling system be needed?

This hasn't been done before, so all input is welcome

Ah yes, we use mainly mac's here but now have vague recollections now of the old 150's being cranked up to 166? - that would have been over a decade ago?

And yip, it's a dual 168 / dual chip / dual IC / dual socket, but we're going to call it our "Dual Core 168" because it sounds cooler.

Applications, ummmm - dunno really, we're only using it for [ serial --> master --> slave <---> serial ] so in that regard, it's an inexpensive  plug-in solution for adding a second serial buffer, which means we're not having to wrestle with software serial anymore, nor do we need to use a wiring board which solves the same problem, but is bulky and costs a lot. We've had one of those here gathering dust for over 3 months, but we like this idea better because it uses a lot less real estate.

The no-frills design is an elaboration of this:-

http://art364.pbwiki.com/Standalone+Arduino

And Paul Badgers RBBB design.

how would you control each individual atmega's with one usb connector?
and wouldent it be better to make digital pins range from 0-26 instead of  2 sets of 13 pins? that way coding would be esier, same goes for analog inputs...

a Siamese Arduino great concept it may have many uses

While an Arduino128 or the SiameseDuino is an excellent option for new purchases, I think an IO expanding shield with a second I2C slaved Atmega128 on it and a second set of IO pins might be a good option for existing Arduino owners.

Very nice and very useful idea.

Will you be selling the PCB's?

John_Ryan wrote on 16.03.2008 at 20:57:15:

As an IO shield, I don't know that you'd need a resonator, the AtMega should be OK at 1/2 speed on it's internal RC clock; otherwise, they're a matter of a dime or so.


John_Ryan wrote on 16.03.2008 at 20:57:15:

If you did it right, the shield would only need to be programmed once, with generic I2C code, and never again. This could either be done by programming the micro in another board (a ZIFDuino?) and transferring it to the shield, adding an ICSP header and using a programmer, or adding a TTL-serial header and using something like the Arduino Mini USB Adapter or the FT232 cable.

I have a fair portion of the slave I2C code written, I'll see if I can write the master library and design a shield proof-of-concept in the morning.