"Crescit enim cum aplitudine rerum vis ingenii"

Publius Cornelius Tacitus


electronics design

  • - redraw the 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
  • extra credit: measure its operation

For this week's assignment we had to redesign the Fab Academy's hello-world board with some own additions. Corresponding with this we had also to check the design rules and afterwards to make the board and finally we had to test it.

After I reviewed different applications regarding electronic design, my decision led to EAGLE from Autodesk even when the handling is somewhat unusal but it's fine for me at the moment. Also KiCAD seems quite interesting and worth a closer look. When my skills and my understanding in electronics design get better I will review my actual choice of PCB design tool but right now EAGLE is the tool of my choice.

Below now is my very first own made schematics and for as much I understood until now everything looked good. I must also say that my Instructor Daniele Ingrassia is doing a amazing job, he can explain things in a short but complete manner.

Instead of just duplicating the given design, we are asked to modify the design by adding some components/functonalities and test them. So I decided to use a switch and two LED'S with current limiting resistors to prevent the LED's from getting "toasted". A current limiting resistor in series with the LED is used to control the amount of current that is going through the LED. If too much current is going through a LED, it will burn out too fast. If too little current is going through it, it might not be enough to lit the LED. In my case the value is a bit higher to prevent the LED from using to much current so that more current is available for any attached devices. When I finished with the schematics design I double checked with the buildin DRC/ERC.

DRC = determines whether the physical layout of layout satisfies a series of recommended parameters called design rules
ERC = involves checking a design for all electrical connections that are considered dangerous, this might include checking for well and substrate areas for proper contacts and spacings thereby ensuring correct power and ground connections and unconnected inputs or shorted outputs.
The basic workflow was equal to the 4th week's task - the electronics production - after finishing the design in Eagle I exported the PCB layout as image/png for further processing. And here a technical problem occured - when I exported the png from Eagle everything looked allright -from the visual aspekt. But as soon as I loaded the file into the fabmodules or in an imageeditor the size were scaled up about a factor 2!

I'll tried different resolutions - from 600 dpi to 1500 but every time the same effect. And scaling down was not an option - especially not when it was about soldering smd's with a footprint less than a mm.

So I asked one of my fellow students if he could export my file on his system (windows) as I owned a MAC and this was one last thought that could made the difference. And yes - this was the solution - the export worked out perfectly. Everything came out as it should be sharp clear and in the right size.
So I loaded the png file into the fab modules - selected the Roland mill and the traces 1/64 than I adjusted the orientation and position of the tool. Following images/screenshots show the process from sketching to layout.

After the milling came the soldering of the components, and a final check against shortage or broken traces. But luckily everything was fine and working. So the final step was to program my new board with a function to proof that it works. To do so I used the Arduino IDE and the example sketch "Blink".

at the beginning there should be always the Datasheet - if available..
...the result looked alright...
here the sections that I added to the original board
the ERC check ...
...and the final EAGLE layout
alternatively the schematics in Circuits
...the milliing traces in fab modules
...the finished milled pcb board
and the soldered finalist.
...running test after uploading the blink sketch! It works!


Exported from assign_board_v3.sch at 08.03.17 17:38
EAGLE Version 8.0.2 Copyright (c) 1988-2017 Autodesk, Inc.

Assembly variant:

Part     Value          Device               Package     Library 

C1       22p            CAP-UNPOLARIZED      C1206       fab     
C2       22p            CAP-UNPOLARIZED      C1206       fab     
C4       1u             CAP-UNPOLARIZED      C1206       fab      
CRISTAL  20Mhz          CRYSTAL              2-SMD-5X3MM fab     
FTDI     6              PINHD-1X6/90         1X06/90     pinhead  
IC1      ATTINY44-SSU   ATTINY44-SSU         SOIC14      fab      
ISP      P6             PINHD-2X3-SMD        2X03SMD     fab      
LED1     Green          LED                  LED1206     fab      
LED2     Yellow         LED                  LED1206     fab      
R1       499            RES-US1206           R1206       fab      
R2       10k            RES-US1206           R1206       fab      
R3       0              RES-US1206           R1206       fab     
R4       10k            RES-US1206           R1206       fab      
R5       499            RES-US1206           R1206       fab      
R6       0              RES-US1206           R1206       fab      
R7       0              RES-US1206           R1206       fab      
SWITCH                  6MM_SWITCH6MM_SWITCH 6MM_SWITCH  fab      


Finally there a view things to mention - the EAGLE application is not bad to start with, even if some handling issues from my point of view are dissapointing. It is not as intuitiv as expected, also I had some "freeze" issues, where I had to restart the application, luckily without any data loss. Than this bug with the png export - I'll have to unistall the package and reinstall to see if this clears the issue. And as Neil commented already - the Autorouter function - is a nice feature, but even me as a newbie didn't convienced that function at all.
Yes, I tried the autrorouter, twice to be precisely - and both times were the result let's say a clear motiviation to sit down and to do it manually. What can I say, I really enjoyed it some how and I'm looking forward to do more complex boards in the future.

I will have a try on KiCad, because it looks promising and I will review this page after done so. The CAD applications Designspark and MultiSimBlue unluckily don't exist for OSX just for windows - so I couldn't check them out within the assignment week. I'll have to see if I can make a review some what later.

Fab Academy 2017
FabLab Kamp-Lintfort Germany