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Electronics design

I started this week assignement a few hours ago… I decided to mill a pretty simple board using Eagle embeded in Fusion360.

I began by importing every library I needed. I first imported the fab.lbr but to my mind , some simple component are missing. I found an another library from a fabacademy student online. The fab_new.lbr is much more convenient. This library provide the Attiny412 which I decided to play with. This library also provide a 3 pin connector very useful for updi.

I began by importing all my components into the shematic project. Then I place it trying minimizing the wiring mess. The Supply2 library from eagle cloud is very useful to simplify the power supply wiring.

I then wired everything. Exept… The button, A that time I forget to wire button to the attiny… I fixed that later :()

Then I switch to the Board designer. A the begining, a mess… All the component were spread over the board…

I reordered everything and place them trying to minimze the PCB size and the wiring mess.

Then I use the autorouter to route everything. I use the basic design rules supplyed by fabacademy. But even the autorouter is helpful, it is limited. It is good to give an idea of how the design may look, but we need to route things mannualy after that. The autorouter didn’t find a 100% solutions at the first time. I had to look for impossible connection and I move my components to help him finding his way trough the circuits.

I finnally got this automaticaly generated result. After a few iteration I got a convenient design that I may work with. Even if the parts are all connected, The path wasn’t very elegant. I moved a few route manually. Here is the ajusted board :

I was pretty ok with the design a that point. but unfortunately I didn’t checked my connection.. Even at 2:00 am I was sure about my work. As expected I forget to connect the button the the Attiny. I can fix that by using an external wire. (I regrets)

Even so, I used Mods to mill my PCB. I had to generate a png using Fusion/Eagle… I manage to find a process : - 1 : Hide all PCB layer except the top layer - 2 : Go to document -> print - 3 : Export a PDF with the smallest page format possible & using black/white color. - 4 : Open the PCB with inkscape to convert it to a PNG or SVG - 5 : Open it with mods

I bought myself a sainsmart genmitsu CNC to mill pcb at home. I had to characterize the machine again. I set the right parameters in mods to mill the linetest again.

I use Grbl controller to control my machine

I successfully milled these traces. The V mill can be very precise when new. I use two different V mill. One for the traces, the other for the outline.

I figure out that when I use a V mill for outline, then I loose a lot of precision on the next trace cutting. Using only a bit for engraving prevent shearing too much the mill.

Another problem I got was about cutting depth. I use the supplyer parameters from my pcb board. The parameters sayed my board was 1.5mm thick, but it wasn’t ! It was 1.7mm thick. As expected I didn’t go trough the material…

As a result I as to finish the cutting using sand paper to reduce the thickness of the material behind the cut bottom. I finnaly got my pcb

After this test I imported my PCB PNG in mods. I set the right parameters using this V shaped mill calculator : Link

Because the mill cut wider as it go deeper. So I had to calculate :

Last update: September 23, 2021