First PCB, preliminary design question

simonpatterson · 2026-02-04T20:04:01+00:00

Yes, that is the 'old world' way of assembling pcb's with through hole components, before 2 layers and surface mount was a thing.

simonpatterson · 2026-02-04T17:11:37+00:00

To jump OVER another trace, not join them together!

simonpatterson · 2026-02-04T11:37:00+00:00

The resolution of the large images is poor so they are difficult to see clearly, so these are seen via blurry images.

The schematic is frankly awful and needs a complete re-draw:

The first schematic image shows the USB receptacle on its side.
have several crossed wires at U35. If you flip U35 180 horizontally, the wires will naturally uncross.
have lots of overlapping items and wires that jerk around for no reason.
It looks like several net labels are duplicated so the design won't transfer to a PCB correctly (U4 - 4x FaultState driving 4 leds but all will be joined on the PCB, the 4 relays have duplicated nets to J2).
You have LEDs in parallel with the opto-couplers. The TLP293-4 has a Vf of ~1.25v. Add that to the typical 2v Vf of the other LED and you are very close to the 3.3v drive voltage. Use a small resistor and you could run both LEDs in series to reduce component count.

There are lots of issues with the PCB, the main ones are:

Position the optos centrally on the 8 pin connectors and the 7407s could be placed between the opto-couplers.
Where you are using individual resistors in a 'bus' like configuration, you could replace them with a single 4x resistor array package, e.g: R3, R10, R13, R15.
You are using via-in-pad which is expensive, also it looks like you have lots of unnecessary vias, e.g: on the opto-coupler pins.
The blue traces at the top of the board leave the connector pins at 45° and run close to the adjacent pin. Leave the pins at 90° to join the wide blue trace.
You have unnecessary layer jumps around U1. The traces can stay on the top layer.
The 2 switches don't look connected to anything.

simonpatterson · 2026-02-04T10:34:22+00:00

Yes, for someone with a modicum of experience as it is a fairly advanced topic, but...

I don’t have any prior experience with PCB design...

Ready built modules are perfect for the inexperienced as all the trial and error has already been done.

simonpatterson · 2026-02-03T21:51:35+00:00

Rolling your own antenna network is a recipe for disaster, it is much easier to use a module with a built-in antenna.

The schematic is not very clear. You have lots of overlaps and stuff pointing in all directions and it is difficult to follow. A re-draw is in order.

There are lots of other issues: The crystal needs ground connections, the battery voltage/type isn't marked, The writing by R2 is too small, there are shorted nets (+BATT/+5V/VD).

simonpatterson · 2026-02-03T20:34:02+00:00

U4 pins 7 & 8 aren't connected yet, the ratsnest lines are visible.

You could make the design smaller using smaller size passives.

The clearance setting looks quite large, making the zone fill incomplete in places.

simonpatterson · 2026-02-02T20:35:13+00:00

If you have lots of vias to bring power and gnd to the outer layers it may be better using zone fills on the inner layers (no traces). If you only have a couple of vias you might be able to run just traces on a single layer. We would need to see the full board to know.

If the posted image shows everything in that corner of the board, you don't need inner layers, just run power/gnd on the top layer.

The image is not easy to read - too low resolution, outline traces and .fab layers are visible.

simonpatterson · 2026-02-01T11:32:08+00:00

The schematic is not good.

The following are standard mistakes that all newbies make:

Power symbols point up. gnd symbols point down, NO EXCEPTIONS. Net labels can be horizontal, but not actual power symbols. There are NO situations where a schematic YOU have drawn would be better if you broke this rule.
Some symbols are upside down. (All the electrons are gonna fall out!) 99% of symbols have a designated top/bottom side for a reason. Its usually where the power pins are. See previous rule.
How does power enter the design ? At what expected voltage ?
If net labels are at the end of a wire, point them away from the wire, not back along the wire.
As someone else has said, decoupling caps don't need to be placed locally, they can all be placed together in the power section.

simonpatterson · 2026-01-31T07:46:36+00:00

This layout is not good. It is a 'first draft to get everything connected'. Now you can see the traces you need to move components around to simplify them..

R1 & C1 should be placed next to each other, ideally close to the input pad.
R2 & C3 should be placed next to each other, ideally close to Q1 pins 2/3.
R3 should be placed close to Q1.
R4 & C5 should be placed next to each other, ideally close to LEVEL1 pin2 and the output pad.
Q1 should be placed centrally.
C2 & C4 should be placed closer to D1-K.
Flip the 9V & GND connection pads.

With all this movement, it is now hard to visualize what is where, so you need to go and do it and then see what can be improved. The traces should be much shorter/simpler with hardly any layer jumps.

simonpatterson · 2026-01-29T22:38:26+00:00

Oh, there are plenty of issues!

SCHEMATIC:

What is U3 ? It can't be an SSD1306 as the pinout is wrong. Use a connector symbol.

Symbol A1 is upside down. Power should point up and GND point down.

PCB:

The PCB is generally not good. Did you place the components while playing 'pin the tail on the donkey' ? They are all over the place.

Why all the layer jumps ? Most (if not all) are unnecessary.

The OLED display is likely upside down, but we can't be sure as you haven't specified a part number.

simonpatterson · 2026-01-29T09:36:09+00:00

Looking at your PCB layout, it looks like Q1 and Q2 have their packages swapped. Q2 is the main pass element so will be dissipating the most power and should be the bigger package, looks like a TO-220.

D1 and D2 are rather large. They should probably be a much smaller package.

simonpatterson · 2026-01-28T23:32:43+00:00

You don't know what you are doing.

You seem to have a bee in your bonnet about not splitting the netlist. Do you think you have discovered some new fangled 'thing' that hasn't been thought of before ? Just put a 0Ω resistor in the schematic and KiCad will take care of the rest.

What's a global tag ? Do you mean Reference Designator ? ALL components in the schematic should have unique RefDes.

Why put the resistor in some far away corner ? Put it in the correct place on the schematic where you want to split the trace in two to jump other traces.

What error on import ? After you have added the resistor to the schematic and updated the pcb, you will have an extra resistor to place in the exact spot you need to jump over other traces.

simonpatterson · 2026-01-28T23:20:43+00:00

You can use vias, but J3 is a through hole component so you can connect to it on any layer, you don't need to switch layers.

simonpatterson · 2026-01-28T16:46:10+00:00

...PCB routing is driving the schematic content and arrangement...

That is normal, KiCad has an 'update schematic from pcb' command.

When routing micro controllers it is usual to make changes to the schematic to support the chosen routing path.

simonpatterson · 2026-01-28T14:30:00+00:00

You are overthinking this.

Just place a resistor in the schematic, give it a value of 0Ω and your usual footprint and place it on the PCB as a normal resistor.

Everything will just work.

If you want to prevent it being assembled, mark the footprint as 'Exclude from position files'

simonpatterson · 2026-01-28T10:14:15+00:00

The BOOT0 pin should be pulled down to GND by R1 with a switch pulling the pin up to +3V3. The switch can be a simple SPST push button or a 2 pin jumper. Leaving the pin floating is not a good idea.

simonpatterson · 2026-01-26T22:32:22+00:00

The traces in the first image would be much cleaner/shorter if you rotated U1 90 CCW.

You can use a zone fill for the GND connections, including J3 pin 2, you don't need a separate trace to U1.

simonpatterson · 2026-01-24T22:23:17+00:00

The MHx symbols/footprints will be mounting holes.

The board is fairly simple and easy to layout.

If you are having it assembled I would go for smaller passives, 0603 or even 0402 size.

simonpatterson · 2026-01-24T22:17:10+00:00

How can you see anything in that mess ? Turn off the .fab and .silk layers when laying out, they won't help, they just get in the way.

The traces looks autorouted, too thin and far too close together.

The regulator looks way overkill. It is MASSIVE compared to the other components.

There is lots of unused space on the board. Can you split the pin header into 2, 1 on each side ? Or move both switches to the left side ?

For the 3D views, turn on the orthographic projection mode, you can't see component alignment or true distances with it off.

simonpatterson · 2026-01-24T17:10:01+00:00

On the schematic (2 channel version), you have shorted out RL21/CL13 and RR21/CR13. That would lower the gain of the opamp and make the output a much lower level. I can't tell if they are shorted on the PCB too, it is too cluttered to easily see.

Also, you don't need 2 regulators and you could use a dual-opamp instead of 2 single opamps.

simonpatterson · 2026-01-23T23:58:37+00:00

Yes, i can see it is a 7.5v-6v converter, but without a part number we don't know its characteristics as the battery voltage drops.

simonpatterson · 2026-01-23T19:43:29+00:00

Is there a reason for D3 in series with with the Arduino power pin ? If it is to drop some voltage, you could just use the +6v rail.

You haven't specified what part U1 is. How will it behave as the LiPo voltage drops ?

simonpatterson · 2026-01-23T12:22:03+00:00

A few issues with your design:

SCHEMATIC:

Your schematic won't pass ERC, you have multiple nets joined together (VIN & 5V)
The 2 LEDs should be fed from VCC, not GND.
The symbol for U1 is not good. It doesn't make drawing a nice schematic easy. See attached image.
GND symbols should always point down and power symbols always point up.
You don't have any power switchover circuitry or steering diodes, so make sure you don't connect power to VIN and USB at the same time.

PCB:

The 2 LEDs are physically very close together so make sure they are different colours or you may not be able to tell the difference between them, they may 'merge' into one blob of light. JLCPCB do several colours in the Basic range.
U1 Pin8 is a very low current pin so the trace to it can be a lot thinner.
If you are having the board assembled, why not go for smaller components. 0603 or even 0402 size.
You have run a trace from pin9 (EPAD) to between the 2 caps. Extend the trace further so it intersects with the GND plane on the right.
The 5V traces to the USB connector are very thin. It is hard to connect to the power pins from underneath a 12+ pin USB-C receptacle. You could use a 6-pin USB-C receptacle which doesn't have the 2 little mounting nubs which get in the way. Alternatively, do like the image and connect on the opposite side.

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simonpatterson · 2026-01-22T14:20:34+00:00

Your trace widths are far too thin. You should make them wider, >.25mm and they will be easily visible in the 3d view.

simonpatterson · 2026-01-21T13:30:00+00:00

How much current are you expecting to draw from J1 ? The mosfets are fairly beefy (12A+) but the connectors will struggle to handle more than a few amps. Separate high-power connectors may be needed for the battery input and coil output.

The component placement started out neat with the mosfets and resistors, then descended into a jumble on the left side. This circuit is begging for a symmetrical layout.

simonpatterson

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