Learning how to PCB... I need some help!

[bem22]

Hello everyone! I am new to this forum and I was steered here by stackexchange.

I decided to dive into electrical engineering recently. I have never drawn a schematic in my life before. I study computer science and most of the stuff I have learned in university is coding/theory about hardware.

I decided to change that and, with my final year project, I am going all-in into electrical engineering.

I am here to ask questions and show off my project which is quite intricate. There's probably an easier way for solving the problem that my project tries to, but right now, this is where I am and I've almost made it work this way to the best of my knowledge.

What is my project?
I am building a drone on the DJI F450 frame that flies using 4G transmission. To control the drone, I ditched the RF remote and I am using an android phone (hence 4G) and an xbox one S controller. To receive data I am using a raspberry pi zero and an USB modem with 4G sim over USB. The pilot is quite dated: MultiWii 2.4, but it runs well on ATMega328P with which I have experience from using it on arduino. Therefore, I am transmitting a PPM signal from raspberry to arduino.

I would like to be able to review my board/schematics in steps and this is mainly why I joined the forum.

Status of my board

I have managed to put together most of the components. I have selected the ICs, the packages for capacitors/resistors/leds etc and I must make sure I am connecting them properly.

You can see my schematics here: https://easyeda.com/be.mihai22/project-hawk

Some notes:
- I am running two i2c busses. One for ATMega328P and one for RaspberryPi.
- I am using one master (ATMega328P) and 3 slaves on the first bus
- I am using one master (RaspberryPi) and 1 slave on the second bus
- 5V(BEC) is from the BEC from the ESCs - I get 3A 5V from BEC x 4. This will power up all the components on the board.
- 3V3 is from the LDO that step-downs 5V(BEC) and powers all sensors+atmega328p at 3V3, thus no level-shifting is necessary for the bus (A problem I had in the past - see https://electronics.stackexchange.com/questions/477343/i2c-level-shifting-2n7002dw

I have a few questions now:

1) Is it safe to use a capacitor for the ICSP interface (MICRO schematic) for the reset pin? Will it be the same pin as DTR for the FTDI?
2) What do you guys about this overall?
3) Could you recommend me some improvements to make the board/schematic/end result more professional?

I have 4 pieces of feedback gathered from other sources:
1) The HMC5883L should have a 4.7uF polarized capacitor on the C1 line (replace of 2.2uF)
2) VDD on the HMC5883L should have a capacitor placed close to the power pins
3) Filter VDDA (analog reference voltage) with ferrite bead (130mA?)
4) Research reverse voltage protection (diodes?)

1) How do I recognize a polarized cap? What package? What is it made of? Examples?
2) What value? Can someone explain how much capacitance for voltage in general? How do you calculate that?
3) What properties should the ferrite bead have? My LDO outputs 130mA max at 3V3. Should I consider that for the ferrite bead? Why/Why not?
4) How do I do this? What kind/properties the diodes should have?

Thank you so much for getting to the end

[bem22]

Hello again, I came back with some updates. I have almost finished the traces and I would like to verify this with you guys.



Here's a preview to the critical bits.

See my project and the schematics here: https://easyeda.com/be.mihai22/project-hawk

The current file is called "LATEST" for the boards

[bem22]

Anybody with experience?

[jfitter]

Here is how you do it (from experience):

• Hang around PCB fab facilities like a bad smell. Soak up every scrap of knowledge you can.
• Ditto - PCB assembly facilities.
• Pay the owners if you have to - most though will let you in because it is in their interests to create good designers.
• Study every professional PCB you can get your hands on.
• Research PCB and component failure modes and design solutions to these.
• Research layout techniques - books and manufacturer notes.
• Research assembly processes and how your design impacts the success of assembly - design for manufacture.
• Make simple circuits first and monitor how long they last.
• DIY FMEA - learn how to and actually do it.
• Build your own reflow oven and experience the gazillion ways the process can fail.
• Make circuits - lots of them - preferably simple circuits. You will get better at it.

Making circuits is an art form. Become an artist. If it looks ugly it may not work, and certainly will not last too long.
Autorouters make ugly circuits (except for memory arrays).

Sit back and take in the whole picture. Design with images not words. Analytical design is boring. The true artist uses inspiration.

Sorry to say but the pic you posted is un-manufacturable. It could be hand assembled but there will be serious reliability issues.

You will get better at it.
Just keep doing the stuff in the list above. We really need software engineers that are good at hardware, and vv. It's not a war - we are all on the same side.

[i_am_fubar]

The idea that PCB design is art is something I whole heatedly agree with.

You will learn facts - "Long traces have a higher inductance"
You will learn realities - "a higher inductance make circuits ring"
You will then form your design patterns - "Gate driver and MOSFET need to be close" "Don't put vias between them" "Keep traces fat"... etc

Eventually, the patterns that break your personal design patterns will look ugly.

Oh, and NEVER assume you know it all. Always be open to learning a new way of doing something and weigh it up with your current approach until you are happy to adopt or reject.