Electronics design

group assignment: use the test equipment in your lab to observe the operation of a microcontroller circuit board, group assignment can be found here

Tektronix TBS 1202B-EDU Digital Oscilloscope#ATTINY 412 echo-hello world board
individual assignment: redraw an echo hello-world board, add (at least) a button and LED (with current-limiting resistor) check the design rules, make it, and test it. Extra credit: simulate its operation
Autodesk Eagle#Roland SRM-20 milling machine

Autodesk Eagle

Schematic

I have never had to design any electronics. It means this week I was carefully trying to follow Antti's instructions. He suggested us to use Autodesk Eagle, and introduced step-by-step instructions how to work with the software.

At first we installed Autodesk Eagle and fab.lbr library for Eagle, which contains all the components used in Fablab Academy.

Having the scheme of echo hello-world board as an example we started the design.

In the Eagle Control panel go Options> Directories and indicate the path to the Eagle library. Now libraries can be seen in a vertical list on the left panel. fab.lbr should be enabled by clicking on it, grey dot will change to green, denoting the activation.
In the Projects go to projects folder and create the New Project (also should be activated with a green dot appearing). From the New Project> New> Schematic.

Fig 1. Starting new project in Autodesk Eagle

We started the shematic.sch drawing.

Fig 2. Starting Schematic in Autodesk Eagle.

Add part tool opens up the list of the components from the library. When we tried to search for ATtiny part, we got no results on it in the existing library.
That means we have to find the part footprint somewhere else. We found ATTINY 412 on SnapEDA. The symbol is missing, but there is a possibility to build it with an option Build Symbol.

Fig 3. Starting Schematic in Autodesk Eagle.

When we signed in on SnapEDA, we could start building the part. Having a Pinout sketch (page 8of the datasheet) on the left we added Pin names and numbers in the table on the left.

Fig 4. Building the ATTINY 412 part on SnapEDA.

The new part should be moved in Eagle library directory to be added to the library.

Fig 5. Importing the part in to Autodesk Eagle.

This was a nice experience, cause we realized, that ATTINY412-SSNR , is not the right type we need. Before we managed to generate another part for the type right type ATTINY412-SSF, Antti has already sent the right footprint to us. The part can be added to the library, and then it appears among the available parts.

Fig 6. Importing the part in to Autodesk Eagle.

To build the scheme of the board we used the following tools:
Add part - add part from the library (select VALUE)

Move and rotate - move parts and change the part's position

Net - toll to connect the parts

Fig 7. Finished schematic of the board with a list of used parts.

Layout

To proceed with a board Layout editor click on Cenerate/Switch to board icon. Things appeared quite messy, and we started arranging them with Move, rotate tools and drawing airwires with Route Airwire tool. We set a width of a wire to 16 mil. Grid tool allows to set the distance between the paths, default value of 50 mil can be changed by holding Alt. Be sure to do this being on the Top layer, which is marked with red color.

Fig 8. Layout generated from the Schematic.

Ground is created by drawing the Polygon around the board and naming it GND. It can be removed by running the command ripup GND.
Rastnest tool is used to update the layout of wires every time they were moved.
Design Rules Check (DRC) parameters are defined with DRC tool and applied with Apply button. The Airwires appeared in my list I easily fixed by slightly changing the path.

Fig 9. Defining Design Rules Check (DRC) parameters and checking the design.

With a Dimension tool the size of the board can be checked. We reserved the space for 6 Pin header positioning.

Fig 10. Reserving the space for 6 Pin header.

To draw the outlines for cutting the board we set the working layer to Milling (layer 46), and draw the the 40mil thick (for 1mm milling bit) outline with Line tool from the left menu.

Fig 10. Final PCB layout with all the Layers active.

To export the PNG image for Traces: Top Layer> File> Export> Image> Monochrome> Resolution 2400. Same steps for exporting Outline, except active layer should be set to Milling Layer.

Fig 11. Exporting the PNG image.

NOTE

After exporting the PNG files we realized, that size of the image has been changed to a significantly bigger dimensions, despite that all the size related settings were right in the Eagle. Eventually we realized that Display in the User preferences should be unchecked for an adequate exporting.

Fig 11. User preferences for Display to cancel scaling the exported images.

PCB Milling

I used Mods to generate the .rml files for milling. The used settings are on the images below:

Fig 12. Generating .rml files for Traces and Outline.

Fig 13. Basic steps for milling prepartion and final result: checking the flatness of the FR-1-PCB blank, cutting the piece of the blank, fixing with a double-sided tape, milling and removing the superficial layer.

Soldering

Fig 14. Soldered components on the board.

Programming and testing

I used the UPDI programmator made during Week 4. Electronics Production. My soldering looked absolutly fine, however the programming would fail every time. We started looking closer on the board to find a possibile mastake, but everything looked good. Until Antti's professional eye found the problem - ATtiny microchip was shifted exactly by 1 pin to the ground. My GND was milled in a way that it looked like a trace. I couldn't resist and soldered the pin to the GND.

Fig 15. Trying to program the board. Even the "precious" board can have a flaw.

Weaponed with a hot gun I fixed ~~friday evening mistake~~ the chip's position. Programming went successful.

Fig 16. Programming the echo board with Arduino IDE. hello.t412.echo.ino program burned on ATtiny returns an echo typed in Putty command prompt.

FILES:

Reflection

This week went fine as I was mostly just following the instructions. I'm trying my best to understand the electronics, and hopefully it will become more clear:)

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