PCB HELP

Everything about the board.

What each file and connector actually is, and a start-to-finish walkthrough for ordering the board — bare or fully assembled — from JLCPCB or any fab that takes Gerbers.

1 · Understanding the PCB 2 · Ordering from JLCPCB

Understanding the PCB

// what everything means

The board at a glance

The SmartCart V2 board is a 45 × 50 mm, 2-layer PCB that replaces the breadboard build. The ESP32 dev board plugs into the two long header rows in the middle (U1), and every sensor connects to a labeled header on the edge — no loose jumper wires. The entire back copper layer is a ground pour, which keeps sensor readings quiet.

U1
ESP32 dev board socket — two 15-pin header rows. The brain plugs in here, so it stays removable.
J1
3.3V · GND · DOUT · HX_SCK — the HX711 load-cell amplifier (force sensor) header.
J4 / J5
3.3V · GND · SDA · SCL — I²C headers for the MPU-6050 (accel/gyro) and AS5600 (wheel encoder). Both sensors share the same I²C bus.
J6
GND · TXD0 · RXD0 · IO0 — serial/programming header for flashing firmware without USB.
J2
3.3V · GND — power input from the TP4056 charger / battery board.
R1 – R3
Small SMD resistors — I²C pull-ups on SDA/SCL and support circuitry. These are the parts JLCPCB assembly solders for you.
C1 – C3
Decoupling capacitors — they smooth the 3.3 V supply so sensor readings stay stable.
D1
Protection diode on the power input — guards against a reversed battery connection.

What the files mean

A PCB is manufactured layer by layer, and each file describes one layer. Gerber files (.gbr) are the industry-standard drawings; Excellon files (.drl) tell the fab where to drill. F_ means front (top) and B_ means back (bottom).

Edge_Cuts
The board outline — where the router cuts the 45 × 50 mm shape out of the panel.
F_Cu / B_Cu
The copper layers — actual traces that carry signals (front) and the ground pour (back).
F_Mask / B_Mask
Solder mask — the green coating. These files mark the openings where copper stays exposed so you can solder to it (the gold pads).
F_Silkscreen / B_Silkscreen
The white printed text — pin labels like SDA, GND and reference designators like R1.
F_Paste / B_Paste
Solder-paste stencil — used by assembly machines to squeegee paste onto SMD pads before parts are placed.
PTH / NPTH .drl
Drill files. PTH = plated through-holes (pins and vias that conduct between layers). NPTH = non-plated holes (bare mounting holes).
.gbrjob
Job file — metadata describing the stackup (2 layers, 1.6 mm FR-4) so the fab's software checks everything is present.
BOM .xlsx
Bill of Materials — the shopping list of components (which resistor values, which diode), used by the assembly service to source parts.
CPL .xlsx
Component Placement List (a.k.a. pick-and-place) — the X/Y position and rotation of every part, so the machine knows exactly where each one goes.

Ordering from JLCPCB

// step by step, with assembly

The whole order takes about 10 minutes. Steps 1–4 get you bare boards (~$2–4 for five). Steps 5–8 add JLCPCB's assembly service so the small SMD parts arrive already soldered. PCBWay and other fabs work the same way with the same files.

You'll need the Gerber zip plus the BOM and CPL files from the PCB page.

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GOOD TO KNOW
✓Assembly only covers the small SMD parts (resistors, capacitors, diode). The ESP32, sensors, and headers are through-hole — you solder or plug those in yourself, following the Build Manual.
✓Minimum order is 5 boards — build spares, or outfit a whole class set.
✓If a part shows out of stock, JLCPCB suggests substitutes — any part with the same value and footprint works.
✓Skipping assembly entirely is fine too — all SMD parts on this board are hand-solderable with a fine tip.