Wattplot Controller v1 — PCB Design Specification

STALE — written for the v1 PCB (ESP32-WROOM-32E, BMI160 IMU, WS2812B status LED, DPS5005 MPPT path, GPIO4/16/17/18/19/21/22/25/32/33/34/35 pinout, K1 relay for the grow light, J7/J8/J9/J10 connector map). The current hardware is schematic rev B (2026-08-03) on ESP32-S3-DevKitC-1-N16R8, with the IMU / WS2812B / relay / limit switches / DPS5005 removed. The block diagram and high-level design notes are still useful, but the BOM, netlist, and pin map need to be regenerated. See:

• Pin map: docs/pinmap.html
• Schematic: docs/schematic.html (rev B, 2026-08-03)
• Firmware config: firmware/wattplot.yaml
• Firmware quick-start: firmware/README.md

A future pass will regenerate this doc against the current schematic. Tracked in ROADMAP.md.

The custom PCB for the Wattplot v2 smart-folding controller. This document is the complete specification: schematic, netlist, BOM, board layout, and assembly notes. Hand it to KiCad / EasyEDA / JLCPCB’s free DFM service to produce the actual board.

Source of truth: firmware/wattplot.yaml defines the pin map. The PCB matches it 1:1.

1. Block diagram

                              ┌──────────────────────────────────────┐
                              │  Wattplot Controller v1 (50×70 mm)  │
                              │                                      │
   12V LiFePO4  ──────────────►│ J1 (XT60) ──► 12V rail            │
                              │                  │                  │
                              │            ┌─────▼─────┐            │
                              │            │  12V→5V    │  buck      │
                              │            │  (MP1584)  │  switching │
                              │            └─────┬─────┘            │
                              │                  │                  │
                              │            ┌─────▼─────┐            │
                              │            │  5V→3.3V  │  LDO       │
                              │            │  (AMS1117)│            │
                              │            └─────┬─────┘            │
                              │                  │                  │
   ESP32-WROOM-32E ◄─────────┤ 3V3 rail          │                  │
   (USB-C, WiFi/BT ant.)    │                  │                  │
                              │   ┌──────────────┼──────────────┐   │
                              │   │              │              │   │
                              │   ▼              ▼              ▼   │
                              │ GPIO16/17/18   GPIO21/22      GPIO26/27│
                              │   │              │              │   │
                              │ ┌─▼──┐    ┌─────▼─────┐  ┌─────▼─────┐│
                              │ │DRV │    │ I2C bus   │  │  reserved  ││
                              │ │8871│    │ (3V3)     │  │ (DNP on    ││
                              │ │    │    │  BMI160   │  │  mini, used││
                              │ └─┬──┘    │  INA219   │  │  on full-  ││
                              │   │       │  ext hdr  │  │  size MPPT)││
                              │   │       └───────────┘  └───────────┘│
                              │   │                                     │
                              │   ▼                                     │
                              │  Linear actuator (4" stroke)          │
                              │                                      │
   Battery V sense ──────────►│ GPIO33 (10k/10k divider)             │
   Soil moisture ────────────►│ GPIO32 (capacitive, 0-3V)            │
   DS18B20 ──────────────────►│ GPIO4  (4.7k pullup to 3V3)          │
   WS2812B status LED ───────►│ GPIO25                              │
   Limit switch 0° ──────────►│ GPIO34 (external 10k pullup)        │
   Limit switch 90° ─────────►│ GPIO35 (external 10k pullup)        │
   Grow light relay ─────────►│ GPIO19 (low-side switch, 12V)       │
                              │                                      │
                              │ J2 (4-pin) ext I2C + 3V3 + GND        │
                              └──────────────────────────────────────┘

v2.4 mini build: GPIO 26/27 and the J4 footprint are DNP (do-not-populate). The Sunapex 10A MPPT is standalone with no host connection. The 26/27 pads and J4 footprint are reserved for the full-size v2 build, where a larger MPPT (Victron 100/30 or EPEver 4210AN) talks to the ESP32 over VE.Direct / RS-485 for telemetry.

2. Power tree

Three rails, derived from a 12 V LiFePO4 battery:

Battery fuse: 5 A resettable PTC on the 12 V input (DRV8871 is rated 3.6 A continuous; 5 A gives headroom for stall currents).

Reverse polarity protection: P-MOSFET on the 12 V input (e.g., AO3401A).

Power flow on startup:

1. Battery → 12 V rail (through fuse + reverse-polarity protection)
2. 12 V → 5 V (MP1584)
3. 5 V → 3.3 V (AMS1117)
4. ESP32 boots from 3.3 V
5. ESPHome starts, queries IMU/INA219 over I2C, reads battery voltage via the divider, reads panel V/I via the panel-side INA219
6. State machine boots in FOLDING (safe default) per firmware
7. Sunapex (standalone, on the bed wall) charges the battery from the panel — independent of the ESP32’s state

3. Component BOM (PCB-level)

PCB-level BOM total: 1 × PCB ($5, JLCPCB 5pcs) + ~$30 in components × 1 = $35 per board

4. ESP32 pin map (matches firmware/wattplot.yaml)

Avoided pins (strapping / ADC2 / flash): GPIO 0, 2, 5, 12, 15 are strapping pins. GPIO 6–11 are flash pins. ADC2 is unusable when WiFi is on, so we use ADC1_CH4 (GPIO32) and ADC1_CH5 (GPIO33) for analog.

5. Netlist (signal-level)

NET_12V = J1.p1, F1.in, U2.VIN, K1.coil+, J5.pin1
NET_GND = J1.p2, F1.out, U2.GND, U3.GND, U4.GND, U5.GND, U6.GND,
         U7.S, Q1.E, K1.coil-, all J*.pin(GND), all C_bypass.GND

NET_5V  = U2.VOUT, U3.VIN, U4.VM (motor supply, optional)
NET_3V3 = U3.VOUT, U1.3V3, U5.VDD, U6.VDD, R_pullup_I2C.top,
         R_pullup_DQ.top, LED1.VDD, J2.pin1, J4.pin1, J8.pin2

NET_SDA = U1.GPIO21, U5.SDA, U6.SDA, J2.pin3
NET_SCL = U1.GPIO22, U5.SCL, U6.SCL, J2.pin4

NET_MOTOR_A = U4.OUT1, J6.pin1
NET_MOTOR_B = U4.OUT2, J6.pin2
NET_IN1     = U1.GPIO16, U4.IN1
NET_IN2     = U1.GPIO17, U4.IN2
NET_EN      = U1.GPIO18, U4.EN

NET_DQ       = U1.GPIO4,  J8.pin1
NET_DQ_PU    = R_pullup_DQ.bot   (4.7 kΩ to 3V3)
NET_DQ_PD    = none (1-Wire is open-drain)

NET_UART_TX  = U1.GPIO26, J4.pin3    # RESERVED (DNP on v2.4 mini; full-size MPPT UART)
NET_UART_RX  = U1.GPIO27, J4.pin4    # RESERVED (DNP on v2.4 mini; full-size MPPT UART)

NET_SOIL     = U1.GPIO32, J9.pin1
NET_BAT_DIV  = U1.GPIO33, J10.pin1

NET_LIM_0    = U1.GPIO34, J7.pin1    # external 10k pullup to 3V3
NET_LIM_90   = U1.GPIO35, J7.pin2    # external 10k pullup to 3V3

NET_LED      = U1.GPIO25, R_LED (100 Ω) → LED1.DIN

NET_LIGHT_CTRL = U1.GPIO19, R_base (4.7 kΩ) → Q1.B
NET_LIGHT_OUT  = Q1.C → K1.coil+ (K1.coil- to GND)
                  K1.NO → J5.pin1 (12V out)
                  K1.COM → J5.pin1 (12V in, looped)
                  J5.pin2 = switched 12V → grow light fixture

Note: limit switch pullups are EXTERNAL (10 kΩ on the wires going to the hinge area). The PCB only carries the signal traces.

6. Board layout

Outline: 50 mm × 70 mm, 2-layer FR4, 1 oz copper, 0.2 mm trace/space (JLCPCB’s standard 4-layer would be tighter, but 2-layer is enough at this complexity).

Component placement (top view, looking down at the board):

  ┌─────────────────────────────────────────────┐  ← JLCPCB fiducials
  │  J1 (XT60)                                  │     on each corner
  │   ↓                                         │
  │  [F1] [U7] [D1]  12V INPUT                  │
  │              ↓                              │
  │         [C_bulk] [U2 MP1584] [L1] [C_5V]   │
  │              ↓                              │
  │         [U3 AMS1117] [C_3V3]                │
  │              ↓                              │
  │  ┌──────┐  USB-C (J3)  BOOT  RESET         │  ← Antenna keepout
  │  │ U1   │  J3       SW1  SW2                │     (no copper, no
  │  │ESP32 │                                   │     ground plane, no
  │  └──────┘                                   │     traces under
  │   │ │   │   │                               │     antenna region)
  │  GPIO distribution to:                      │
  │   ├── I2C bus [U5 BMI160] [U6 INA219]       │
  │   ├── GPIO25 → LED1                         │
  │   ├── GPIO4  → J8 (DS18B20)                 │
  │   ├── GPIO19 → Q1 → K1 → J5 (light)         │
  │   ├── GPIO32 → J9 (soil)                    │
  │   ├── GPIO33 → J10 (battery sense)          │
  │   ├── GPIO26/27 → J4 (RESERVED, DNP on mini) │
  │   ├── GPIO16/17/18 → U4 DRV8871 → J6        │
  │   └── GPIO34/35 → J7 (limits)               │
  │                                             │
  │  Connectors along right edge:               │
  │  [J2 I2C]  [J4 — ]  [J5 light]  [J6 motor]│
  │  [J7 lim]  [J8 temp] [J9 soil]  [J10 bat]  │
  └─────────────────────────────────────────────┘

Critical rules:

• ESP32 antenna keepout: 10 mm × 15 mm rectangle at the top edge of the PCB, no copper, no components, no ground plane. The PCB antenna needs this region to be clear.
• High-current traces: 12 V from XT60 to F1 to U2 to motor (J6) should be wide (≥ 1 mm, 1 oz copper = ~3 A). The 12 V rail carries up to 5 A briefly during actuator stall.
• Analog traces (GPIO32, GPIO33): Keep away from switching traces (MP1584 switch node, DRV8871 outputs). Add a ground guard on both sides.
• I2C pullups: 4.7 kΩ to 3V3 on SDA and SCL, near the ESP32.
• Decoupling: 100 nF + 10 µF within 5 mm of each IC’s power pin.
• Mounting holes: M3 at each corner (4 mm from edges).

Cost: JLCPCB 5-piece prototype run: $5 (5 boards) + $15 shipping = $20.

7. Assembly notes

Order of assembly (top side first):

1. Power section (low side): U7, F1, D1, C_bulk, U2 (MP1584), L1, C_5V, U3 (AMS1117), C_3V3. Test with 12 V input: verify 5 V and 3.3 V rails before proceeding.
2. ESP32 + USB-C: J3, U1, SW1, SW2, R_pullups, decoupling. Test: connect USB, flash a blink sketch, verify the ESP32 boots and WiFi connects.
3. I2C devices: U5 (BMI160), U6 (INA219), J2. Test: run an I2C scanner, verify both devices respond.
4. (DNP on v2.4 mini) UART (full-size MPPT): J4. Test on the full-size v2 build only — connect the chosen MPPT (Victron SmartSolar or EPEver Tracer), send a status query, expect an IDN response. The v2.4 mini build does not populate J4 or have any UART active.
5. Motor driver: U4 (DRV8871), J6. Test: bench-test with a spare actuator or a small DC motor. Verify IN1/IN2/EN control direction and speed.
6. Relay + grow light: Q1, D2, K1, J5. Test: toggle GPIO19, hear the relay click, verify 12 V at J5.
7. Sensors: J8 (DS18B20), J9 (soil), J10 (battery), J7 (limits). Test each individually.
8. Status LED: LED1 + R_LED. Test: blink test from ESPHome.

Final assembly:

• Mount the PCB in a waterproof ABS enclosure (e.g., Polycase WC-22F, 4.7”×2.6”×1.4”, IP65). Cut a hole for the USB-C and XT60.
• Conformal-coat the PCB (MG Chemicals 422B silicone) for humidity resistance — optional but recommended for outdoor Phoenix use.
• Mount the enclosure on the bed’s east or west short wall, near the battery. Or external to the bed, on a post.

8. Test points

• TP1: 12 V rail (after F1)
• TP2: 5 V rail
• TP3: 3.3 V rail
• TP4: GPIO33 (battery sense divided voltage, should be ~5.0 V at 12 V battery)

Each test point is a 1 mm pad for easy probing.

9. What this PCB is NOT

• ❌ Not an MPPT. The PCB does no power conversion. Charge control is the Sunapex 10A (mini) or a larger MPPT (full-size v2). The PCB only reads battery voltage through the divider and panel V/I through the panel-side INA219.
• ❌ Not a microinverter interface. The microinverter (Enphase IQ7+ or APsystems DS3) is its own certified box; the PCB doesn’t touch it.
• ❌ Not a solar charger. The PCB monitors and controls the canopy / actuator / sensors; the actual battery charging is the Sunapex’s job.
• ❌ Not a power supply. 12 V comes from the battery; 5 V and 3.3 V are derived for the ESP32 and sensors. The PCB does NOT generate 12 V.

10. Open questions for v2

• Add a small OLED display (SSD1306) for local status without Home Assistant?
• Add a CAN bus header for future expansion (e.g., multiple panels)?
• Add a hardware watchdog timer (TPL5010) to reset the ESP32 on hang?
• Move to a 4-layer board for better EMI/grounding?

These are not in v1. v1 is the minimum viable controller.