Electronics Design

Tutorial, wiki and me

A few months before Fab Academy, I downloaded Eagle and poked around for a bit. At the time, I didn't spend much time with it, did not really understand the libraries, and gave up after a short time. I thought it had been a waste of time, but somehow, when I now began using it, that little experience removed a great deal of the overwhelming nature of Eagle.

I followed the tutorial on how to make the schematic, then followed along with Bas' lecture the next day. I milled the traces and the outline and soldered my components, much like we did when we were making our FabISPs.

No heartbeat!

No matter what I did, the board refused to work, and my attempts at programming it failed. I decided to review the schematics and found my mistake. I had somehow failed to connect the RESET (RST) pins on the microcontroller and the ISP, meaning that the RST pin on the microcontroller was just connected through the 10k resistor to VCC but nothing else.

The reason why we need the reset pin is so that we get the correct bits of code in the correct order, as opposed to starting somewhere in the middle.

It's aliiiive!

Once I discovered the flaw, I connected the two pins with a wire to see if this would fix my issue. Fortunately it did! I redrew the schematic as seen above, and added the trace to my board as seen on the left. Since my board works with the jury-rigged wire connection, I decided not to mill it again, but rather use it as is for now.

I grabbed Neil's code from the Fab Academy archives, and used it without editing it. In order for this string of code to work correctly, you need to download the c file and the py file and keep them in the same folder. Otherwise you must navigate to the correct folder before using the py string.

3 Lines of code

Now that my board worked, I programmed it using my FabISP with the make code from the fab academy website. I plugged it in, loaded the code, downloaded the python code and connected it to the board.

For some reason, it took me a while to understand that I needed to write three strings of code before using the python window to communicate with the board. Once this was in place however, it worked beautifully:

• $ sudo make -f hello.ftdi.44.echo.c.make
• $ sudo make -f hello.ftdi.44.c.make program-usbtiny-fuses
• $ sudo make -f hello.ftdi.44.echo.c.make program-usbtiny

Hello world

Once the code had successfully been programmed onto my circuit, I unplugged the FabISP and connected the circuit directly to the computer using an FTDI cable. I could then use the term.py code to test my board.

• $ python term.py /dev/ttyUSB0 115200

Because it worked, it opened a small python window, where if I wrote something, the circuit board recognized my input and echoed it back. (step by step until my final sentance read: hello.ftdi.44.echo.c: you typed "hello world")

Eagle and you

If you're here for interesting things, follow the link below to skip this boring and rather pointless part. If not, by all means read on and see my own version of the millions of existing tutorials on Eagle

In Eagle, the work area is divided into three windows. The main menu, the schematic and the board. We'll cover each in more detail below. The first step is to download Eagle and install it, then connect your Autodesk account. Then download the fablab library for Eagle, and place it in the library section of your eagle folder. Then in the main Eagle window, turn off all libraries except the Fab lab and Source libraries to begin with. This will save you time when you are getting started on the schematic. For now, click "file" - "New" - "Schematic" to begin!

Schematic

Your empty schematic can be scary, since it's just a white page with nothing on it. Let's deal with that my clicking "add component" It is nice to start with a microcontroller, so go ahead and grab the ATtiny45. Open the fab library and scroll around until you find it.

Schematic pt.2

Open the fab library and scroll around until you find the ATtiny 45. Then click "OK" if you're okay, or cancel if you want to cry because this guide is depressing.

Schematic pt.3

Don't worry too much about connecting the pieces yet. First add all the components you want. In this example, I've added all the components needed for my TinyBLE, a bluetooth module I made much later in the Fab Academy timeline, but which is neatly arranged and pretty and doesn't make me angry to look at, nor think about all the better things I'd like to do with my time than write this guide.

Schematic pt.4

Now you need to connect all the things that should be connected. For example, make sure to connect the reset pin on your microcontroller to the reset pin on your ISP pin header. To connect components, use the "draw electrical connection" button in the left hand toolbar. It looks like a small green "L" that fell down. You can either connect the pins directly with the green line, or you can draw the green line out a short way, then name it. For example, you might name the line "reset". You then draw another short green line where you want to connect "reset" to, then name that "reset" as well. This makes for a neater schematic if your lines would otherwise criss cross across the schematic.

Once you have connected all your pins on all your components, click the "schbrd" button. It's the 4th button in the top toolbar. This will tell you that you don't have a board yet, and ask if you want to create a new one from he schematic. Carefully click "yes". If you click "no", it won't make a new board for you.

Board setup

Before you do anything else on the board window, adjust your drc settings! Bas showed us settings which are good for the Roland Modela, so I usually just load those settings back in. If you want to use them too, click the button below. These settings govern the layer setup, the minimum drill size, allowance, distance between things and much more, and you therefore need to have them in order before you do anything else.

Board layout

All the components are now neatly crammed into the bottom left corner of your board window. They are connected with yellow lines called "airwires" These lines tell you which components still need to be connected. Drag your components onto the table and arrange them as neatly as possible, so that you can draw the traces.

Routing your traces

My favourite settings for routing traces is to have them at width 12, to push obstacles and using wire bend style 1.

Routing your traces

Now you carefully connect all the pieces that need to be connected. If you make mistakes, you can "rip up" traces, or if everything is messed up and you want to start over, you can type "ripup;" and it will remove every trace you have placed.

Preparing for export

Adjust your dimension until your baord is the size and shape you want it to be. It can be square, but it can also be more dynamic in shape You can use the existing lines, or draw a new shape. Use super slim width for this part. Then draw a square on layer 200. This is a bitmap layer, and we will hide it later. We are using it to make it easier to get our png files to be the way we want them to be. Draw the square from (0,0), then place your entire design starting at (5,5). Turn on all layers to see if there are any artefacts on your board that need deleting. Once you are satisfied, hide everything except the top layer.

Exporting

With only the top layer visible, select "File"-"Export"-"Image". Tick the box marked monochrome, set resolution to 1500 dpi. Save this in a place you'll find it, and name it "name.traces" for example, this one is called "TinyBLE.traces" Then go back to the layers and hide everything except the dimension layer. Repeat the steps to export the image, but name this one "name.interior". Immediately open this image in gimp, and use the fill tool to fill the interior with white. Then select "file"-"overwrite name.interior.png".

Exporting

Open the name.interior image in gimp, and use the fill tool to fill the interior with white. Then select "file"-"overwrite name.interior.png". Now your image is ready to be imported into fabmodules. Congratulations.