Seeking advice and review of my first PCB design in EasyEDA

[paronga]

Hi there, long time lurker.

Thanks for the forums and website in general for teaching me so much about electronics over the years. Much appreciated.

I'm working on a project that I am learning PCB design and manufacturing through.
It is a very small board with an ATTINY3216 and some pads for a push button rotary encoder, and some pads for power. It also has some pads for 5V WS2812B LED strips/strings that will be attached. Finally, there is a pad for UPDI programming of the device.

It's pretty stealth and minimal, no LEDs as I find the ones on dev boards extremely distracting in my use cases.

I am seeking advice and comments on my design on how to make this a high quality circuit board.
Here is my TODO:

- Add any required decoupling capacitors.
- Add any other resistors of capactiros that are required for good board design.
- Ensure all traces are appropriate thicnkess. Especially on the VCC and GND rails to the LEDs, I expect to draw 0.5A - 1.5A.
- Add the appropriate USB D+ and D- pads and the required resistors to request higher power from USB A chargers.

Here is a link to my OSHWLab project:

https://oshwlab.com/paronga/attiny3226_001

I am keen to learn!

Thank you

[pcprogrammer]

Hi and welcome to the forum.

I can't answer all of your questions, but here is my 2 cents worth.

You mention decoupling capacitors, and yes they will be needed. At least a 100nF ceramic capacitor close to the VDD (VCC) pin of the MCU, with an as short as possible path back to ground. I would also add a bigger cap near the incoming supply, of which you mention it to be from a USB-A adapter. So you are limited to 10uF, but that will help to clean up the supply a bit.

It might be a good idea to add a small resistor in series with the data line to the LED strip. This will reduce problems with higher communication speeds. Something in the order of 33 to 100 Ohms.

About your schematic, there is room for improvement, especially with a simple design like this. Do not use net labels in this design. Use wires. Start on the left with the power input and end on the right with the LED output. Have the MCU in the center and the rotary encoder on the left of it. Makes it much more readable for others.

Then the circuit board. You choose a double sided board, which is good because it is cheap enough. The routing you chose is not the best. First of all, it is best to use a solid ground plane on the back side of the PCB. Try to keep all the other traces on the top side for as much as possible. The power supply trace needs to be much wider between the entry point and the output to the LED, because that is where the current will flow. The ATtiny will not take much current, so a thinner trace can be routed to the VDD of it. Use something like this site to calculate the needed trace width.

Also try to use 45 degree angles instead of 90 degree angles like you did going from the MCU to the rotary encoder and the LED data line.

Can't help you with the USB power supply resistor combination. Have not looked into that myself, but do be careful as I do know that for more power some adapters can switch from 5V up to higher voltages. Not sure if this is true for USB-A connector based ones.

There is also the option to connect USB to the MCU and use the bit banged USB library to make your project computer controllable. (https://github.com/obdev/v-usb)

Success and have fun with your project.