5. Electronics Design Assignment

Electronics Design Assignment

This assignment was in its own way, very interesting, as I was able to get out of my comfort zone and learn a little more about electronics. We first started from the Hello Board:

Since the assignment was about adding components on top of that, It was time to take a look at the design rules and, in a borader sense, to the whole design process, we used EAGLE in the lab for that, starting from the schematics, which we had to build from scratch in the software:

The most tricky part was selectring the right components out of the huge lubrary we had available, including the libraries supplied for the fab, with so many similar components, it was easy to get confused and choose the wrong one, I made two selection errors, first: the GND, not from the right library, the second was the LED chosen, as it will be shown later.

Slowly adding the components and connections, the device started to take form, I added the switch, a 1K resistor, and the LED, here I made the second mistake, but it would not be noticed until I got to to the PCB stage.

Finally, I had the schematic done. It was time for the PCB stage, here, the LED error became visible, as It shows, I had chosen a trhough-hole component, not the SMD in the Lab Inventory, back to the schematic to correct.

As I was designing, I used the Board Reference model in this stage, which helped. The ERC check showed warnings, not errors..

At that point, I did not know how to select which design layers would actually be exported for the milling, so I ended with a PNG that would need a lot of work erasing and cloning pixels to get it to proper shape, fortunately, a friend helped me to correct this mistake. Still, befor doing this, I realized I had made a few blunders in the milling. Marked in red ther is a track was not properly designed. Correction was in order.

After correcting the mistakes and selecting the proper layers, I had a PCB 90% ready for milling:

Just added a logo using a photo editing software and then I was ready for milling.

I made two versions of the card, one as-is and other one with the same dimensions as the hello board PCB in the academy website, in the end, it was not necessary.

The milling was not to be without incidents, as the first plate I put in the modela was not bonded strongly enough, and got loose as it was milling, Modela 1 - Isaac 0.

After placing a second plate and checking it was properly bonded, it worked, although the z-calibration was not optimal and the tracks were not in its optimal shape, had to try again. The second time, the tracks went better, but some residues were still in the tracks, so some sanding was made before the plate could actually be welded. But first I had to cut the plate using the 1/32' mill, for this I created a new frame for cuttng:

With this I had the plate ready for soldering... or so I thought. As I was starting to add flux to the terminals I realized the center track touched all of the Attiny terminals in the left side, when It was supposed only to touch the fourth from the top, so the most analog solution was to cut those threads using a scalpel, available at the lab. As a sort of Plan B, I modified the PCB design and changed the routing, since what caused this was sending too many routes through the center, under ther Attiny chip.

Modified Routing.

Afterwards, I sent the new design to the Modela, this time without incidents.

This time the tracks were well milled, no copper residues, no missing tracks or separations:

Welding, as in assignment number three, proved somewhat difficult, in particular the resonator, since you need to solder all of the terminals underneath it,and your visibility is not the best to do this, however, after some fully-focused work, it was done:

As a sort of conclusion, I will say that, even though I learnt much about electronics, there is still much to be learnt in order to get succesfully to the final project, also, The timeframe was not enough to get to the circuit simulation, since the learning curve of the necessary sotfware is somewhat steep.