Our instructor this week was Antti Mäntyniemi, organized a workshop where we could all: install eagle, add the fab library, create an schematic with all the parts, and then he gave plenty of tips for creating the board and drawing the routes. And then we had the group assignment

To Do

  1. Create schematic from Neil's design and add led and button
  2. Prepare board: routing
  3. Mill and solder components
  4. Test it (multimeter and programming)

The "Doing"

Designing

Eagle

We are going to use Eagle to design the schematic of the circuit. After downloading and installing, it is necessary to add the fab.lbr, a library with the components available in fablabs. To do so, first download fab.lbr to any folder. Then, open the add menu with Edit > Add. If the fab library is not in the list, then Open Library Manager. In this new prompt, browse for the fab.lbr, and then close the prompt. Now the fab library must be in the list 3d object design

The circuit

First, it is necessary to understand Neil's image of the circuit: identify the appropiate components and see how they are connected to the rest. Also, we needed to add a button and a Led. Moreover, as a recommendation from Antti, we add a filter that would remove the bouncing from the button (explanation at Antti's assignment and debouncing solution and in the group work assignment). When releasing the button, there is a bouncing that sometimes produces big glitches. It is better to filter those so there are no strange effects in our circuit. This is done with a low pass filter.

original board
hello ftdi 44 board
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Schematic for the led
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Schematic for the switch

The schematic

Now it's time to create the schematic. We just need to follow the board above and:

  • identify the elements (names help) in the board
  • get that element from the fab library and place in the schematic
    • Edit > add prompts the add menu. You have to open the fab lib, and look for the component you need, and click Ok
      • VCC and GND are selected from supply1 lib
    • Place the component somewhere in the schematic. The component can later be moved/rotated
    • Press ESC once you are done placing one component
    • connect the different components according to the given board and the datasheets if needed.
      • Draw > Net to draw the connections between components
    • Give values to the components:
      • rightclick a component to show menu
      • value and insert the desired value
    • add component
    Add Component menu
The final result of schematic is: 3d object design
schematic from given board

The board

Once the schematic is ready, it's time to create the real traces. First, we need to press Generate/switch to board button to get the board. It is a representation of the board components joined by airwires.

generate board
Generate board button
board first view
Board first view
All the components have to be placed in the black mat on the right. Then, you need to manually create the routes that cannot overlap. For that, use:
  • Edit > move and Edit > rotate to position
  • Edit > Route to create routes from one component to another
    Once you select route, and click on one component, you get feedback on all the possible endings of the route as seen in the figure on the right
  • Edit > ripout to delete a route
  • Tools > ratsnest to reorganize airwires
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one route started
You should check the Default Rules, DRC , which will give feedback on possible problems. You can also define your own rules in the DRC prompt, as minimum clearance (space) between conductive elements. You can define new values and save those settings for later usage.
Values defined are
Clearance
  • All values for clearance set to 16mill but between wire and wire that is set to 30mill
Sizes
  • Minimum size set to 16mill
Thermal isolation (subtracting pad shapes from signal polygons)
  • Thermal isolation set to 16mill
clearance
new values for clearance
size
new values for size
supply
new values for supply tab
The board has to have our design dimensions: grab the corners of the black mat in the background and put them in the corners of your board design.
Ground layer
To define ground layer as the remaining copper in the board:
  • Draw > polygon: Draw a polygon around your board
  • Edit > Name: Name it GND
  • Tools > ratsnest: To put wires to ground layer
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Outline
The outline for cutting was drawn in layer 46 (milling) with Draw > Line, setting the width to 40
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settings for drawing the line for the outline
outline
outline
The result: 3d object design

Milling and Soldering

traces and outline

Export as images File > Export > Image, with correct whites and blacks. Note that:
  • for my settings, for the outline image, the background must be changed to white (Select white at Options > User interface> Layout)
  • for the outline, you need to see just the layer 46: milling
  • for the traces, you need to just see the layer 1: top
  • select monochrome
  • set resolution. In this occasion I set it to 1500dpi. UPDATE! it is better to 2400dpi
traces
export traces
visible layers menu
visible layers mennu
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outline
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traces
As in in assignment 05, I used fabmodules to get the traces for the milling machine. In this case, I needed to check carefully the output, because with the first settings it did not trace the whole design. Then, I changed the tool diameter to 0.37mm and then it worked.
not working settings
not working settings
working settings
working settings
I afterwards learnt from my mates that exporting the png with higher resolution (I used 1500dpi, and they were recommended by an instructor to use 2400dpi) would prevent that to happen.

milling and soldering

I proceeded as in assignment 05 for milling and soldering the board.

board
board
component list
component list
component missing
component missing in the list
Several notes:
  • I used the multimeter to check there was continuity when it had to be and no shortcuts with the board just cut
  • I used the multimeter again after soldering the components to check the same thing
  • In this case, I had an "issue" (big issue): I managed to break one of the pads from the board when soldering. With Jari's help, I managed to sold it back. (It is the big drop of solder in the 3x2 pin header that is visible in the picture beneath)
board soldered
board soldered (and the big issue quite visible)

Testing

Programming

I downloaded the hello.ftdi.44.echo.c. I also downloaded AtmelStudio as I decided to use it as ide following Antti's recommendation.
I built Build > Build solution the hello file and got a warning
compile 1

So I started to look for the F_CPU value, which I found in the hello.ftdi.44.echo.c.make file (F_CPU = 20000000). I defined it in the file, as the error was F_CPU not defined. I built again and everything went ok. compile 2
I used my programmer from assignment 05 to program this week's board programming settings
In the hello file, it says set lfuse to 0x5E for 20 MHz xtal. I programmed the fuses from the command line 
avrdude -p t44 usb -c usbtiny -U lfuse:w:0x5E:m
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Then, following the link from Antti's, I configured ATMel Studio to work with avrdude as an external tool
avrdude
avrdude as external tool for loading program
  • Tools > External Tools > Add
    • Title: name of this configuration
    • Command: avrdude.exe, with the complete path
    • Arguments:
        -c usbtiny -p m328p -v -v -v -U flash:w:$(TargetDir)$(TargetName).hex:i
      • -c parameter specifies the programmer being used
      • -p parameter specifies the microcontroller (search the avrdude.conf file to find this)
      • -v parameters make sure the output is verbose, so I can check if anything goes wrong
      • the $(TargetDir) and $(TargetName) are Atmel Studio variables pointing to the project folder and the hex filename
    • Initial directory: Path to avrdude instalation
  • Click OK
And I run avrdude with Tools > avrdude. It runs quite fast (TIP: uncheck the close on exit), but I managed to capture the following 3d object design
Just need to test if it is working as expected!

Running the program

After connecting the board to the computer with an FTDI cable, I checked which is the serial port assigned: COM4.
Then, I opened PUTTY terminal and created a session for serial, with Serial line COM4 and speed 115200, which is the baud given in Neil's hello file.

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PUTTY settings
Opening the session opens a command prompt. The hello program is an echo program: I started to press keys in the keyboard:
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output as expected

Resources

Once done

Summary

  • I have learnt to use eagle to design my board: create schematic, route the board
  • I have used the multimeter to check my board connections
  • I have used the oscilloscope for some basic testing
  • I have used my programmer from assignment 05, and it works (!!)

Difficulties

  • ...soldering.... again....

Learnings

  • From others experience: always check continuity with the board

Tips

  • For routing, just start doing it! It gets easier as you go on with the job

Files