small mega328 pcb

June 2010.

After doing the Tiny tiny85 PCB I thought I'd do one for the mega328. I started laying out a PCB using the TQFP but decided skinny and long is a better shape for my stuff.
Being only marginally smaller than a pro-mini I doubt there will be much public interest in this but I'll put it online once it is tested.

The main difference is I have no reset button and use a (optional) crystal instead of a resonator. My work is geared towards TWI not simple serial so the TWI is brought out.
Like the tiny tiny85 PCB all the component sit inside the DIP footprint so for space critial applications the sides of the PCB can be trimmed to the size of the I.C.

A TQFP version may still appear.

Ten PCBs are on order from batchPCB.
ETA late July.

Image Schematic for the 328 DIP.

Image PCB artwork for the 328 DIP.

Image The real thing.

Image The back side of the PCB showing power supply and LEDs.

A TQFP version appeared.

Designing this wasn't totally trivial. Like my tiny85 PCB this one has all the essentials in the middle of the PCB so the sides can be removed if need be leaving a functional micro in a 15mm/0.6 inch square footprint. The inner set of through hole pads are zigzagged because the SF footprint I based it on would pass the batch PCB design rules. It is not intended to take a connector - even finding pins to fit the small hole might be difficult. I expect soldering wire-wrapping wire would work.

I had to go to a smaller regulator and 0402 style caps. The lm3480 should be stable with 100nF ceramics caps but higher values (tantalum) do exist in this tiny packet. Tantalum caps are expensive so ceramics are attractive to lower the cost as well.

As before I've use a crystal (optional). I find the internal RC clock is fine for most things but when I need accuracy I'd rather use crystals than resonators. The crystal is fairly large and uses a lot of the PCB real-estate, almost half the space is taken by the crystal and the loading caps.

The outer pads a standard 0.1 inch and could be used for SIL sockets or wire wrap pins. Stacking a small shield on top would be possible but I'm not sure if the value of doing this - having a large single PCB with a prototyping area might be a better solution.

Image Schematic for the 328 TQFP.

I'm fairly happy with the way it turned out. The power connections are a little awkward but for a PCB which is intended to be embedded it shouldn't matter too much. There is no reset switch but during software development a switch can be clipped on, usually I just use the ISP to do the reset.
There is no ISP port but clipping eze-hooks onto the pins has work fine in the past.
It would also be trivial to make an adaptor so the arduino IDE and loader could be used, this is not my thing but it would be possible.

Image PCB artwork for the 328 TQFP. Isn't it pretty :-)

Image Programming the TQFP via ezi-hooks.

Image The bottom side of the TQFP version of the PCB.

The fuse/lock settings I used for internal RC clock were...
high fuse byte = D2
IFuse = F2
eFuse = 5
lock bits = 2F


Files are in this gallery http://nerdipedia.com/tiki-list_file_gallery.php?galleryId=15
in this file http://nerdipedia.com/tiki-download_file.php?fileId=100

You can also order these PCBs at BatchPCB.
Note these are the batchPCB prices - I don't make a cent from the sale.

TQFP version http://batchpcb.com/index.php/Products/36501
DIP version http://batchpcb.com/index.php/Products/36282


Created by eddie. Last Modification: Sunday 08 of August, 2010 13:08:17 AEST by eddie.

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