sandTable/pcb/archive/v0.3

SandTable Controller v0.3 (custom PCB)

A 2-layer, 80 × 63 mm board that replaces the Arduino Uno + CNC shield in the sand table. It uses the same 4 mounting holes as an Uno, so it fits the deck standoffs.

Status: designed and checked in KiCad, with order files ready for PCBWay. It has not been built or tested yet.

• MCU: ESP32-WROOM-32E (Wi-Fi), running FluidNC. USB-C programming through a CH340C with auto-reset, so no buttons need pressing.
• Motors: 2× DRV8825 StepStick sockets, with 100 µF bulk capacitors. The board fixes the drivers at 1/32 microstepping and keeps them awake: M0–M2, RESET and SLEEP are all tied to 3.3 V. A4988 drivers also fit and run at 1/16.
• Power: 12 V barrel jack with a reverse-polarity diode → RECOM R-78E 5 V switching regulator → AMS1117 3.3 V. USB 5 V and regulator 5 V are diode-ORed, so USB alone powers the logic for flashing. The motors need the 12 V supply.
• Connectors: JST-XH to match the motor cable plugs:
  • 2× motor
  • home switch
  • hall sensor (5 V)
  • WS2812B LED data (buffered to 5 V)
  • 4-pin expansion header
• Copper: ground pour on both layers. The ESP32 antenna sits over a copper-free area at the board edge.

Changes in v0.3

• No holes in solder pads. PCBWay's review of v0.2 found vias inside pads, which they would only build reliably by filling them with resin, for extra cost.
  • The router now keeps every via at least 0.2 mm from every pad. In v0.2, 26 vias sat in or overlapped pads of small parts.
  • The ESP32's 12 ground-pad holes are replaced by one solid copper pad, with the same 9 solder windows.
  • PCBWay can now build it as drawn, with no via filling.
• Parts list: exact part numbers for the 4-pin header (Sullins PRPC004SAAN-RC), the driver sockets (Sullins PPTC081LFBN-RC) and the 100 µF capacitors (Panasonic EEE-FK1V101GP), as agreed with PCBWay.

Changes in v0.2

• Drivers: DRV8825 instead of TMC2209 in UART mode. The serial line and its resistor are removed, so IO16/IO17 are now free.
• Holes: the smallest hole is now 0.3 mm. The ESP32 footprint's 0.2 mm ground-pad vias were enlarged, because PCBWay charges extra for holes under 0.3 mm.
• Order files: a PCBWay order folder (Gerbers, parts list, placement file, assembly drawing, order sheet) replaces the JLCPCB files.
• Silkscreen: VMOT / EN / DIR are printed beside each driver socket.

Checks (KiCad 9.0.7, kicad-cli)

Check	Result
ERC (schematic)	0 violations
DRC (board, all severities) against PCBWay's standard limits: 6/6 mil trace/space, 0.3 mm hole, 0.15 mm ring	0 violations, 0 unconnected
Schematic ↔ PCB parity	0 differences
Vias within 0.2 mm of a pad, holes inside a pad (checked from the board file)	0

Ordering from PCBWay

Everything for the order is in pcbway-order/. ORDER.md there lists the exact settings to enter, which file goes in which upload box, and a note to paste for PCBWay.

File	What
1-gerbers-…zip	Board files: Gerbers plus separate plated and non-plated drill files
2-bom-…csv	Parts list for turnkey assembly, with manufacturer part numbers
3-centroid-…csv	Part positions in mm, origin at the board's bottom-left corner
assembly-top-…pdf, schematic-…pdf	For PCBWay's engineers if they ask

The DRV8825 modules are not on the order; you plug in your own. The back of the board has PCBWay's "WayWayWay" marker, so their order number prints there instead of on the front.

Before first power-up

1. Driver direction. Line up the module's VMOT, EN and DIR pins with the VMOT / EN / DIR labels on the board. A driver plugged in backwards is destroyed.
2. Driver current. On a DRV8825, current limit = 2 × Vref (with the usual 0.1 Ω sense resistors).
   • Start at about 70 % of the motor's rated current. For example, a 1.0 A motor needs Vref ≈ 0.35 V.
   • Measure Vref between the trim pot and GND with the 12 V supply connected.
   • Never plug or unplug a motor while the power is on.
3. Home switch wiring. Connect the switch's COM to HOME pin 3 (GND) and its NO contact to pin 2.
4. Firmware.
   • Flash FluidNC over USB with the FluidNC web installer.
   • Upload fluidnc/config.yaml as config.yaml.
   • In the config, X is theta in degrees and Y is rho in mm. $H homes rho.
   • If an axis turns the wrong way, add :low to its direction pin.

ESP32 pin map

Function	GPIO
Theta (spin) STEP / DIR	IO18 / IO19
Rho (arm) STEP / DIR	IO27 / IO14
Driver enable (shared, low = on, pulled up so the drivers are off at boot)	IO13
Rho home switch	IO34
Theta hall sensor	IO35
LED strip data (through a 74AHCT1G125 buffer)	IO33
Status LED	IO2
Expansion header	IO32, IO25
Free, not connected	IO16, IO17

Files

Path	What
kicad/	KiCad 9 project: schematic, board, and project-local symbol and footprint tables
sandtable-controller-schematic.pdf	Schematic
pcbway-order/	Everything to upload to PCBWay, plus ORDER.md with the settings
renders/	3D renders
sandtable-controller.step	3D model. The copy placed in sand-table-v2.solidcraft is v0.1, which has the same outline and holes.
fluidnc/config.yaml	FluidNC machine config (a starting point, not yet run on hardware)
tools/	Python generator: design.py (parts, placement, nets, sourcing) → route.py (router, ground pour, board file), sch.py (schematic), fab.py (PCBWay order folder, renders, copy into this folder)

To regenerate everything, run python3 tools/route.py && python3 tools/sch.py && python3 tools/fab.py. The KiCad files are built in ~/kicad/sandtable-controller because the KiCad snap can't read inside ~/snap/.

Notes

• 5 V budget: the 5 V regulator supplies 0.5 A. That covers the ESP32 plus a short LED strip (about 10 LEDs at full white). Use a separate 5 V supply for longer strips.
• Noise: DRV8825s are louder than TMC2209s; expect some motor whine. TMC2209 modules in standalone mode might work in these sockets, but their pin layouts vary by brand, so check before trying one.
• LED strip: FluidNC doesn't drive the WS2812B header. It's there for other firmware or an add-on later.