CE351 Microcontrollers
Power Supply Circuit for MCUs
James Ferguson
8/30/2020

Objective
The goal of this lab was to create a general purpose PCB that converts 6V - 12V DC to 5V and 3.3V DC at 1A or 3A. This PCB should be ablke to produce stable DC voltages. This project mostly followed this tutorial by Dr. Li. Altium Designer was used to create the schematic and layout components to create a circuit board. This was chosen over Eagle PCB for the sole reason of using this lab as an opertuinity to gain experiance with a new piece of software.

Schematic
This design uses a 6 x 2 pin array (J1) for power selection where alternating shorts selects either 1A or 3A. 1117 voltage regulators (U1, U2) are used for 1A power, while LM2596 DC-DC converters (U4, U5) are used for 3A power.


Layout
Parts where laid out roughly in 5 sections: I/O, 5V 1A, 3.3V 1A, 5V 3A, and 3.3V 3A. Trace width was set to 40mil and routed by hand.

Top


Bottom
While Altium has more support for images than Eagle PCB, it seems to only support rasterized images. Within the editor it doesn’t look too good due to the pixel density being low compared to the close zoom. This will hopefully look more professional when actually manufactured and the image is only about an inch tall.


3D Render


Generating Gerber files
Altium generates more files than necessary to manufacture a PCB and some of them can cause errors, specifically with using PCBWay, the wrong file was used as the board outline resulting in misshapen or missing boards. This was fixed by removing some unnecessary files. The list of files I ended up with was as follows:
PCB1.apr
PCB1.GBL
PCB1.GBO
PCB1.GBP
PCB1.GBS
PCB1.GKO
PCB1.GPB
PCB1.GPT
PCB1.GTL
PCB1.GTO
PCB1.GTP
PCB1.GTS
PCB1-RoundHoles.TXT
PCB1-SlotHoles.TXT
Here, PCB1.GKO defines the board shape. These gerber files where checked with PCBWay’s online viewer and gerbv for errors before sending the files off for fabrication.

Results
10 units arrived form PCBWay. A single board was assembled. during assembly some issues where noticed. The pads for 4.7F, 33F and the barrel jack where too small which made soldering very difficult. This however posed no issue to the board’s functionality. The bottom silkscreen also visually suffers from the relatively low resolution as the individual pixels are clearly visible.
Bare PCB
PCB with Components

The following shows the PCBs 3.3V output (yellow) and 5V output (blue) at both the 1A and 3A confiurations.
1A
3A



Discussion
This PCB generates 3.3V and 5V power at both 1A and 3A as desired. DRC runs throwing showing no errors. View the DRC report here. Personally, I think Altium Designer, while less intuitive than Eagle PCB, appears to be more feature rich and versatile piece of software. For future designs I should look more into manufacturing export settings, image imports, as well as review the built in component libraries before using.