Seeking Advice On PCB

fab
1

Hello All!

I’ve tinkered with electronics for a few months and I’m totally hooked! I’ve mainly been working on creating remote controlled cars with different types of Arduinos and NRF24l01 transceivers. I’ve successfully created a couple different breadboard designs and decided to try and create a custom PCB for the remote transmitter. I hope to make the car receiver PCB in the future. I’m a complete beginner at PCB design and I would love some feedback.

Here is a description of the remote. The 3 JST connectors will go to an 18650 battery pack, a WS2812 with 10 LEDs at half power and a small 8ohm 1 or 3W speaker. I plan on using an NRF24l01 as a transmitter and take user inputs through 2 10k Joysticks, 2 10k potentiometers to control servos, a gyroscope for tilt controls and 2 buttons for sounds/music. There will be an SD card for playing sounds that are triggered by different events. I will have a plastic cover attached to the drill holes on the 4 corners to protect the electronics and mount the battery pack, speaker and lights to. I’ve laid this out on a breadboard and tested all the different components successfully (minus the lights).

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Remote.fzz (51.4 KB)
Here are some newbie uneducated questions and concerns I have with my design:

1.) I’ve been watching some PCB design videos and had a question about ground planes as it relates to my project. I routed all my ground connections but can I just do a ground fill and remove all my routed ground connections with no issues in my design?

2.) If I do a ground fill, I’ve watched some videos about how the return path for high frequency signal traces don’t use the shortest path but instead use the space below the trace. I tried, as much as possible, to not interrupt the space below traces and run most of my signals on the bottom layer but couldn’t leave the top layer 100% empty for the ground plane. Do you think I will run into issues with signal integrity due to the crossing of traces with my design?

3.) Also on the topic of EMI, I’ve heard about crosstalk in traces with long parallel runs. I have some parallel runs but tried to space them out. I’ve heard a rule of 5x the width of the trace in spacing but I don’t think I could achieve that with my board size. I also tried to keep my power traces on the outside of the board but had to run a power connection directly to the Nano in the center. Do you think I will have crosstalk issues with my design?

4.) I added a separate 3.3v supply to power the NRF because I’ve rarely been able to get the NRF to work from the Arduino’s 3.3v pin. I also read the datasheet on the regulator and it suggests a 10uF cap on the input and output of the regulator. Since this is the only device I’m powering with that 3.3v source, do I still need the 10uF cap near the NRF or will the 10uF cap from the regulator suffice?

5.) I plan to use 2 18650 batteries to power everything and that gives me a nominal voltage of 7.4v. Is there any power supply filtering I should be doing outside the caps for the voltage regulator? I added a 100nF cap near the Arduino but I think there is already a 100nF and 4.7uF cap on the 5v pin. Do I need my 100nF cap in that case?

6.) I plan to play sounds for different events that the car may have using an LM386 on the remote. I’ve gotten the LM386 to work pretty well with the design I put on the PCB. I noticed that I didn’t need to increase the gain by using a cap across pin 1 and 8. It’s really loud already and the volume setting in the TMRpcm library gives me plenty of volume. Do you think the proximity to the SD card will cause any issues like clicking noises while the SD card is reading?

Any other advice or criticism is very welcomed!

2

The sketch passes DRC and looks OK as is (you likely don’t need ground fill, it is likely an added complication you don’t need.) I would advise rearranging and fully routing schematic though. It is extremely easy to make a mistake in pcb and get something wrong. That will show up as an incorrect connection in schematic and thus is a good check that the board is indeed correct.

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You want to space out, rotate and move the parts around til schematic gets wired in a reasonable manner then click on the rats nest lines and route the wires and make sure they go where you expect (here I deleted all traces leaving only the rats nest lines.)

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selecting the part and right clicking on it gives you the rotate menu. You want to be careful with the 18650 batteries, shorting them is a really bad idea (fire or explosion) as is over loading them. A fast blow fuse in the battery lead is probably a good idea in case of a short (which will blow the fuse and disconnect the batteries (hopefully fast enough.) Otherwise it seems OK.

Peter

3

Thanks for your response!

Oh true. I started moving things around when I laid out the components but didn’t go back to it after wiring everything in the PCB. If I wire everything in the schematic tab, will it tell me if there is a missing connection on the PCB tab?

I’m not quite sure how I would do this. I do have the protected button top batteries that says it protects against shorts, overcharging and low voltage. Can I add a fuse to my PCB or to the battery case?

4

If the schematic tab says “routing complete” as opposed to the current 25 of 30 nets routed (which correspond to the rats nest lines still visible in schematic which indicate connections in breadboard or pcb that aren’t routed yet in schematic) then the schematic matches pcb. If the resulting schematic matches the connections you expect then things should be fine. I circled in red some of the rats nest lines it is indicating aren’t routed.

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Then you shouldn’t need the fuse (although, yes you can either put one on board on the pcb or in line with the battery off the pcb.) The main thing is to make sure schematic matches the circuit as you expect it to avoid cutting the pcb and discovering it is wrong when you wire it up. I note that some of the SMD capacitors are mounted on the bottom of the board in pcb. I assume that is intended to put them on the bottom of the board (by default they are on the top and you have to move them to the bottom?)

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Peter

5

Thanks! I’ll get that fixed and cleaned up.

Yea, I moved them to the bottom. I was planning on using standoffs and some hard plastic as a case for both top and bottom layers. I’m not very well versed in how things are typically done, is that a bad design choice? I guess I could use through hole caps for those but I was trying to keep the caps and resistors as unseen as possible. I felt like I had to use that one through hole 10uF cap to get the wiring correct. I also have some other SMDs on the bottom layer for the SD card, voltage regulators and JST connectors. Should I move them to the top layer?

6

No it is just unusual, and sometimes people move the part to the bottom of the board by clicking on the bottom selection in Inspector without being aware they have done, it which is why I asked to make sure it was intentional and not by accident (and a surprise when the board comes back :slight_smile: )

No need to, as long as you are aware they will be on the bottom it shouldn’t be an issue. I thought it was likely intentional but it always pays to ask to make sure.

Peter

7

You’re a legend! Thanks for the advice Peter! You’ve helped me a ton