sandTable/pcb/README.md

SandTable Controller v0.4 (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: v0.4 is designed and checked in KiCad, with order files ready for PCBWay. It has not been built yet. v0.3 boards have been ordered; their files are kept in archive/v0.3/, and "Using a v0.3 board" below lists what to watch for on them.

• MCU: ESP32-WROOM-32E (Wi-Fi), running FluidNC. USB-C programming through a CH340C with auto-reset, so no buttons need pressing. ESD protection on the USB data lines.
• Motors: 2× DRV8825 StepStick sockets, each with a 100 µF bulk capacitor plus a 10 µF ceramic right at its power pins. 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 (at 1/16) after bridging solder jumper JP1.
• Power: 12 V barrel jack → 2.5 A resettable fuse → reverse-polarity diode → RECOM R-78E 5 V 1 A switching regulator → AP7361C 3.3 V low-dropout regulator. 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 (pin order matches the Arduino CNC shield: each coil on an adjacent pair)
  • home switch
  • hall sensor (5 V supply)
  • WS2812B LED data (buffered to 5 V)
  • 4-pin expansion header
• Inputs: the home and hall inputs have a pull-up to 3.3 V, an RC filter and a clamp diode to 3.3 V, so a 5 V sensor or module can't overdrive the ESP32.
• Copper: ground pour on both layers, stitched with about 350 vias. The ESP32 antenna sits over a copper-free area at the board edge.

Changes in v0.4

From a design review of v0.3. None of these stop a v0.3 board from working; they add margin and make the board safe for other people's parts.

Area	v0.3	v0.4
3.3 V regulator	AMS1117: needs about 4.4 V in, but only gets about 4.5 V after the OR diode, so the rail could sag during Wi-Fi bursts	AP7361C-33E: 0.09 V dropout at 300 mA, stable with ceramic capacitors. Different pinout (1 IN, 2 GND/tab, 3 OUT); never swap in a 1117-type part
5 V regulator	R-78E5.0-0.5 (0.5 A): not enough for the ESP32 plus an LED strip	R-78E5.0-1.0 (1 A, same footprint). The OR diode D2 is now a 3 A SS34
Driver supply	100 µF capacitors 19 mm from the VMOT pins	Plus a 10 µF 50 V ceramic across VMOT and GND at each socket (C16, C17). They sit between the socket strips, under the module
Driver pin 2 (FAULT on DRV8825, VDD on A4988)	Tied to 3.3 V: safe only on modules with a series resistor on FAULT	Solder jumper JP1, open by default. Bridge it only for A4988 modules
Home / hall inputs	A 5 V sensor module with its own pull-up could push about 4 V into IO34 / IO35	BAT54 clamp diodes to 3.3 V (D6, D7), after the 1 k series resistors
12 V input	No fuse	Bourns MF-MSMF250/16X-2 resettable fuse (2.5 A hold, 5 A trip)
USB	No ESD protection	USBLC6-2SC6 on D+ / D−
Motor traces	One at 0.3 mm, the rest 0.5 mm	All 0.5 mm (about 1.5 A each); the router may not narrow motor or 12 V traces
Ground	29 ground vias, 3–4 under the ESP32	About 350 stitching vias, about 100 under the ESP32
Motor plug pin order	Coil pairs on pins 1–2 and 3–4	Same pairs, in the driver's own order (as on the CNC shield). An axis may now turn the other way than on v0.3: see "Firmware" below

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
Pinouts of every active part checked against its datasheet or KiCad's library symbol	ESP32, CH340C, AP7361C, 74AHCT1G125, R-78E, USBLC6, MMBT3904, USB-C, driver sockets
Fit in the sand table (v3 shell and deck)	Board corners 3 mm from the wall, clear of the deck bosses; jack and USB next to the cable notch

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 type. DRV8825: leave JP1 (under the theta driver socket, marked "A4988 ONLY") open. A4988: bridge JP1 with a blob of solder, or the A4988 has no logic supply.
2. 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.
3. 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.
4. Home switch wiring. Connect the switch's COM to HOME pin 3 (GND) and its NO contact to pin 2.
5. 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.

Using a v0.3 board

The v0.3 boards work; the v0.4 changes add margin. On a v0.3 board:

• Random resets or Wi-Fi dropouts, mostly on USB power alone: the AMS1117 is short of headroom. Run from the 12 V supply, or replace U3 with a low-dropout regulator that has the same pinout as an AMS1117 (pin 1 GND, pin 2 OUT and tab, pin 3 IN). ST's LDL1117S33R is sold as one; check its datasheet's pin table before buying. The AP7361C used on v0.4 has a different pinout and does not fit a v0.3 board.
• DRV8825 clones: check that the module has a resistor in series with its FAULT pin, as Pololu's does. If not, clip or bend that pin (FAULT, between A2 and the last GND on the motor-pin row) so it doesn't plug in; a DRV8825 doesn't need it.
• LED strip: the 5 V regulator gives 0.5 A in total, which leaves room for only 2–3 LEDs at full white.
• Hall sensor: use a bare open-collector sensor (A3144 style), not a breakout module with its own pull-up to 5 V.
• Motor traces: fine up to about 1.2 A per motor.

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
fluidnc/config.yaml	FluidNC machine config (a starting point, not yet run on hardware)
archive/v0.3/	The v0.3 board as ordered: KiCad files, order files, schematic and the generator's design.py
tools/	Python generator: design.py (parts, placement, nets, sourcing) → route.py (router, ground pour, stitching vias, board file), sch.py (schematic), fab.py (PCBWay order folder, renders, copy into this folder). place_new.py finds free spots for parts added in a revision

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 1 A. The ESP32 takes up to about 0.4 A during Wi-Fi bursts, which leaves about 0.6 A for an LED strip: roughly 10 WS2812B LEDs at full white, or more at lower brightness. On USB power alone, keep the strip off; USB gives 0.5 A in total. Use a separate 5 V supply for longer strips.
• Input voltage: 12 V. The fuse is rated 16 V, so don't use a higher supply.
• 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.