# SandTable Controller v0.4 (custom PCB)

![render](renders/render-iso.png)

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/`](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/`](pcbway-order/). [`ORDER.md`](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.