Milestone 04: First Schematic and Board Design Draft

[rajborra]

Couple of preemptive comments:

I'm changing my design to use the Arduino instead of the FPGA: I realized from the reference designs online that implementing the FPGA involves more than just adding the input (button and clock) and output connections, and that some deviations from these relatively complex reference designs may cause the FPGA to not work. As a result, I think I'll stick with the Arduino: I will try to get my updated software pushed to GitHub soon.

As for the Eagle schematic/board I created:

• Since I very recently changed back to the Arduino design, I may have missed a couple of components I may need in general. I also think I have the headers that should be connecting to the Arduino, but I'm unsure if there is a specific header size / type that I need to use.
• I'm not sure if I was able to find the exact resistors/capacitors types that were in the class parts library, so those may need to be changed?
• I have a GND plane in place on the bottom layer of the board, but despite the polygon I placed being poured in, I don't think my GND net is resolved or connected at the moment. The idea is to have both the top and bottom planes to be set to GND once this is finished though.

Finally, a general question: what is preventing us from reducing the board size / product by just placing the ATmega328 MCU (and not the rest of the Arduino) on the PCB? For example, is there a way where we can program the MCU using the Arduino, and then remove it and place just the MCU on the board? This question is more out of curiosity.

[sphaerobolus]

It's fairly straightforward to pull the ATMega328 from the UNO board and use it on a board of your design. You'll need a voltage regulator, probably. you'll probably also need a crystal and two capacitors to provide the clock. Not much more than that. You would not be the first to do this.

I don't see any design files.

You probably don't need a plane on top and bottom. This means less copper to remove in fabrication, but doesn't significantly improve performance here.

[rajborra]

Is the voltage regulator that would generally be used (the one currently in the design) not enough for the ATmega328? And I'm guessing I can use whatever crystal / capacitors the Arduino board provides to the MCU normally.

I think the .sch file is pushed as well? I can attach a PDF of the design file if necessary.

Will it be enough to have a ground plan on the top then? I would have no bottom plane connections at all then.

[sphaerobolus]

Ah. I had missed the subfolder with the design files. Sorry for the confusion.

So you need only have one .sch and one .brd file. You want to be committing and pushing from the desktop client to update the file on the server. All of the separate files for old versions kinda goes against the spirit of version control.

It is enough to have just one plane. No connections on the bottom is just fine.

The voltage regulator you have is sufficient if you use a bare ATMEGA328. It's unnecessary if you're building a shield. The UNO and Nano both have regulators on board, so you can take advantage of them. In the case of UNO and Nano, put your 9V into Vin pin. The Arduino will make 5V available to you out of the 5V pin.

Same for crystal. If you're not using a bare '328, you do not need to provide the crystal.

CN1 is not a footprint we have. You could use a 2 pin header, with pins spaced at 0.1" (100mil) here.

The the regulator package you're using is in a package we do not stock. We have them in the TO-220 and TO-92 packages.

Is this intended to be an UNO shield? Your two headers should be one part, with pins labeled with their signals. You don't have to do this work; these are available for download for the UNO. The UNO won't fit on the headers here. The pins are in four groups, spaced weirdly.

[rajborra]

I edited my schematic with all of the above: please let me know if I may have done something incorrectly!