Wattplot v2 — Build Guide

STALE — written for the v2.4 / ESP32-WROOM-32 + BMI160 IMU + limit-switches architecture. Pin numbers, sensor names, and entity IDs in this doc do not match firmware/wattplot.yaml v3.2. Use this as design intent (the build phases, sequence, and mechanical steps are still valid) and cross-check the electronics steps against:

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 YAML. Tracked in ROADMAP.md.

Step-by-step assembly of the entire apparatus. Follow the order below. Each step lists the time, tools, parts, and verification.

Total build time: ~10-15 hours over a weekend (with lumber pre-cut).

Total cost: ~$1,400 (per the BOM at bom.md).

Phase 0: Pre-build (Day 0, ~1 hour)

0.1 Order lumber

From the BOM at bom.md:

12 × 1x6x8ft cedar (bed wall skin, 4 courses per wall)
4 × 2x4x8ft PT DF (wall cleats, 16 × 22” cuts)
2 × 2x6x8ft PT DF (wall caps, hinge + strut walls)
2 × 2x6x8ft PT DF (long rails)
2 × 2x6x8ft PT DF (cross rails)
1 × 2x4x10ft PT DF (diagonal brace)
1 × 2x4x8ft PT DF (fixed-tilt struts, Basic tier)
2 × 4x4x8ft PT DF (skids)

If your lumber yard offers FSC-certified DF, request it (small premium). FSC chain-of-custody: ask for the certificate.

Tip: many yards will cut to length for free or a small fee. Have them cut:

8 × 1x6 @ 96” (long wall skin, no cut needed from 8ft)
8 × 1x6 @ 43.1” (short wall skin, 2 per board from 8ft)
16 × 2x4 @ 22” (wall cleats, 4 per board)
2 × 2x6 @ 96” (wall caps, no cut)
2 × 2x6 @ 96” (long rails, no cut)
4 × 2x6 @ 42” (cross rails, 2 per board)
1 × 2x4 @ 102” (diagonal brace, cut from 10ft)
2 × 4x4 @ 96” (skids, no cut)

If they don’t pre-cut, you’ll need a circular saw or miter saw. None of the cuts are mitered (90° only). A standard circular saw is enough.

0.2 Order hardware

4 × galvanized butt hinges 4”×4” leaf, ½” pin (Home Depot)
1 × ½” × 72” steel rod (Home Depot, in the steel rod section)
6 × aluminum mid-clamps 35mm channel (IronRidge / Unirac)
1 × ECO-WORTHY 12V 4” stroke 330 lbf linear actuator (Amazon)
1 × ½” × 3” clevis pin (McMaster)
8 × 3/8” × 4” carriage bolts HDG + washers + nuts (Home Depot)
8 × 5/16” × 3” lag bolts HDG (Home Depot)
24 × ¼” × 3” deck screws HDG Torx T-25 (Home Depot, 1 lb box)
1 lb box × 3” exterior deck screws (general)

0.3 Order the panel + electrical

1 × 620 W bifacial panel (LONGi Hi-MO X10 or similar)
1 × 12V 100Ah LiFePO4 battery (LiTime or similar)
1 × 30-40 A MPPT charge controller (Victron SmartSolar 100/30 ~$200, or EPEver Tracer 4210AN ~$140). See §7 below. The DPS5005 used in earlier revisions is retired — it was both a UART-controlled hack and undersized for the 620 W panel (5 A output, would have thrown away ~90% of the panel’s potential).
1 × 12V LED grow light (20-30W, full spectrum)
1 × ESP32-WROOM-32E dev board (or use the PCB from docs/pcb_design.md)

0.4 Order the PCB (optional but recommended)

Send the design from docs/pcb_design.md to JLCPCB (5 pieces for $5+shipping). While you wait (1-2 weeks), continue with the mechanical build.

Phase 1: Bed (Day 1, ~3 hours)

1.1 Build the wall cleat frames

The walls are 1x6 cedar skin (¾”, non-structural) screwed to vertical 2x4 cleats that carry the soil pressure. All square cuts, no notches.

Tools: circular saw, drill, impact driver, square

Process:

Cut 16 cleats: 2x4 @ 22” (4 per 8-ft board).
Long walls get 5 cleats each: one at each end, three between at ≤24” on center. Short walls get 3 each (ends + middle).
Stand a wall’s cleats on a flat surface and screw the bottom skin course (1x6 @ 96” long walls / 43.1” short walls) across them with 2 × #8 × 1¼” exterior screws per cleat. Square as you go.
Add the remaining 3 courses. Top of the 4th course = 22”.

Verification: each wall panel is flat, square, and 22” tall with cleats flush at top and bottom.

1.2 Assemble the bed box

Tools: drill, impact driver, square, level

Process:

Stand the 4 wall panels up. Short-wall skin ends butt into the long walls’ end cleats — corners join cleat-to-cleat, not skin-to-skin.
Screw each corner: 4 × #10 × 3” exterior screws through the long wall’s end cleat into the short wall’s end cleat.
Lay the 2x6 caps flat on the south (hinge) and north (strut) walls, screwed down into every cleat top with #10 × 3” screws. The caps are what the hinges and strut shoes bite into.
Check the bed for square: measure diagonally both ways. Should be equal (~105” each).

Verification: bed box is 96” × 44.6” outside, walls plumb, corners square, caps flush with the outer skin faces.

1.3 Attach the skids

Tools: drill, ¼” bit, impact driver, square

Process:

Flip the bed upside down.
Place two 4x4x8ft skids under the bed, aligned with the long walls. The skids extend 0” past the bed ends (flush).
Pre-drill 4 holes per skid (2 per end), ¼” pilot bit, through the skid and into the bed wall.
Drive ¼” × 3” deck screws through the skid into the wall.

Verification: skids are flush with the bed ends and square to the bed. The bed sits flat on the skids.

1.4 Place the bed at the site

Tools: level, shovel (if site prep needed)

Process:

Move the bed to its final location. The bed is heavy (~150 lb empty, ~2000 lb with soil). Get help.
Level the bed in both directions (use shims under the skids if needed).
The bed should slope slightly toward the south (1-2% grade) for drainage. Adjust shims.

Verification: bed is level (or slightly tilted south), skids are fully supported, no wobble.

Phase 2: Frame (Day 1, ~2 hours)

2.1 Assemble the frame rectangle

Tools: drill, ¼” bit, impact driver, square, measuring tape

Process:

Lay the 4 frame rails (2 long + 2 cross) on a flat surface.
The cross rails fit between the long rails. Butt joints at the corners (no miter).
Pre-drill 2 holes per corner (through the cross rail into the long rail end), ¼” pilot bit.
Drive ¼” × 3” deck screws.
The frame interior should be 93” × 42” (PANEL_L - 2*RAIL_T) × (CROSS_RAIL_L).
The frame exterior should be 96” × 45.6”.

Verification: frame is square (measure diagonally), 96” × 45.6” outside, 93” × 42” inside.

2.2 Add the diagonal brace

Tools: drill, ¼” bit, impact driver, measuring tape

Process:

The 2x4x102” diagonal brace runs corner to corner inside the frame.
Position the brace so its ends butt into the inside faces of the long rails.
The brace is at the height of the rails (sits on the bottom inside face of the long rails, or just above).
Pre-drill 2 holes per end (through the brace into the long rail inside face), ¼” pilot bit.
Drive ¼” × 3” deck screws.

Verification: brace is at the correct diagonal angle (~24°), both ends are screwed to the long rails. Frame is now rigid (no racking).

2.3 Install hinges on the bed’s south wall

Tools: drill, 5/16” bit, impact driver with socket, measuring tape

Process:

Lay the frame on top of the bed, with the frame’s south rail resting on the bed’s south wall.
Position the 4 hinges evenly along the south rail: spacing 22”, centered, 4” margin on each end of the 96” wall.
Mark the hinge positions on both the frame’s south rail and the bed’s south wall.
Pre-drill 4 holes per hinge (2 per leaf), 5/16” bit for the lag bolts.
Attach the wall leaf of each hinge to the bed’s south wall with 5/16” × 3” lag bolts.
Attach the frame leaf of each hinge to the frame’s south rail with 5/16” × 3” lag bolts.
The frame should now hinge freely on the south wall.

Verification: frame hinges smoothly between 0° and 90° tilt. No binding. The ½” hinge pin holes in all 4 hinges are aligned (the continuous pin will pass through all 4).

2.4 Insert the continuous hinge pin

Tools: mallet (rubber), ½” drill bit (if pin is too tight)

Process:

Thread the ½” × 72” steel rod through all 4 hinges, starting from one end.
Tap gently with a rubber mallet to seat the pin fully.
The pin should extend ~1” past the last hinge on each end.

Verification: pin is fully seated. The frame hinges smoothly with the pin in place.

Phase 3: Panel (Day 2, ~1 hour)

3.1 Lift the panel onto the frame

Tools: helper(s), ladder if needed

Process:

The 620 W bifacial panel weighs ~65 lb. Get help.
With the frame flat (0°), place the panel inside the frame, centered.
The panel frame (aluminum) should sit on top of the wood frame.

Verification: panel is centered, frame interior clearances are even on all sides.

3.2 Clamp the panel to the frame

Tools: drill, 5/16” hex driver, M8 wrench, ladder if needed

Process:

Place 2 mid-clamps per long rail (4 total), at positions ±24” from the panel center (4 evenly spaced clamps along the 96” rail).
Place 1 mid-clamp per cross rail (2 total), at the panel center (each side of the panel, where the cross rail meets the panel).
Tighten the M8 bolts to clamp the panel frame to the wood rails.
Torque to ~10 Nm (snug, not crushing).

Verification: panel is firmly attached. Try to wiggle it — should not move.

3.3 Install the actuator

Tools: drill, ½” bit, 9/16” wrench, 2× helpers

Process:

The actuator is between the bed’s north wall and the frame’s north rail.
Mount the wall-side clevis block (2x6 PT, 6” long) on top of the bed’s north wall, near the bed’s center.
Mount the frame-side clevis block on the inside face of the frame’s north rail, near the bed’s center.
The actuator’s body is on the frame-side, the rod extends toward the wall.
Pin the actuator to the wall block with the ½” × 3” clevis pin.
Pin the actuator’s rod end to the frame block with another clevis pin (or use the same pin if the actuator has both ends pinned).

Verification: actuator is mounted, rod can extend and retract. Frame can be tilted by hand from 0° to 90°.

Phase 4: Sensors and Wiring (Day 2, ~3 hours)

4.1 Install the IMU on the frame

Follow docs/sensor_placement.md § 1.

Tools: drill, #4 wood screws, small Phillips, foam adhesive pad

Process:

Mount the BMI160 breakout board on the underside of the frame’s north rail, centered.
Use 2× #4 wood screws through the breakout’s mounting holes.
Add a small foam adhesive pad between the breakout and the wood to dampen vibration.
Run the 4-wire I2C cable along the north rail to the cable carrier.

4.2 Install the limit switches

Follow docs/sensor_placement.md § 6.

Tools: drill, small wood screws

Process:

Mount the 0° switch on a small wood block on the bed’s south wall, just below the hinge axis. The roller faces the frame’s south rail.
Mount the 90° switch on a small wood block on the bed’s north wall, near the actuator mount. The roller faces the frame’s north rail.
Test by tilting the frame by hand:
- At 0° (flat), the 0° switch should be pressed.
- At 90° (vertical), the 90° switch should be pressed.
Run the 3-wire cable (signal, signal, GND) from the switches to the PCB.

4.3 Install the soil sensors

Follow docs/sensor_placement.md § 3-4.

Tools: shovel, drill (for grommet holes), screwdriver

Process:

Drill a ½” hole in the bed’s south wall, 12” from the east end (for the soil cables).
Insert a rubber grommet in the hole.
Push the DS18B20 probe into the soil to 6” depth, 12” from the south wall, 24” from the east end.
Push the soil moisture sensor into the soil to 4” depth, 18” from the south wall, 24” from the east end.
Run the cables through the grommet, up the south wall, into the cable carrier, to the PCB.

4.4 Mount the PCB enclosure

Tools: drill, #10 wood screws, level

Process:

Mount the PCB enclosure on the bed’s east short wall, at table height (~30” above ground).
The enclosure should be accessible for service (not buried in foliage).
Use 4× #10 wood screws through the enclosure’s mounting feet into the bed wall.
Verify the enclosure is level (for any internal status displays).

4.5 Wire the PCB to all components

Follow docs/wiring.md.

Tools: wire stripper, JST-XH crimper, screwdriver, multimeter

Process: connect each cable as described in the wiring table. Do not install the battery fuse yet.

4.6 Continuity check

Tools: multimeter

Before applying power, verify:

No shorts between 12V and GND (multimeter continuity)
No shorts between 3V3 and GND
No shorts between 5V and GND
Each limit switch closes when pressed (0 Ω when activated)
All JST-XH connectors are fully seated
No bare wire exposed at any connector

Phase 5: Battery and First Power-On (Day 2, ~1 hour)

5.1 Connect the battery

Tools: multimeter, 5A fuse

Process:

Place the 12V LiFePO4 battery on the ground next to the bed (or in a small battery box).
Connect the battery negative to the PCB enclosure’s ground bus.
Connect the battery positive through a 5A in-line fuse, then to the PCB’s J1+ terminal.
Do not install the fuse yet. Leave the fuse holder empty.

5.2 Install the fuse and power on

Tools: USB cable, laptop

Process:

With the laptop connected via USB-C to the PCB’s J3, install the fuse.
The ESP32 should boot. The status LED should light up (any color means power is on).
Open the Arduino IDE or ESPHome flasher. Verify the ESP32 is detected.
Flash the firmware: esphome run firmware/wattplot.yaml.

5.3 Verify boot

Tools: serial monitor

Process:

Open the serial monitor (115200 baud).
Look for ESPHome boot messages. Should see:
- “Wattplot Controller” branding
- “BMI160” detected
- “INA219” detected
- “DS18B20” detected
- State: FOLDING (safe default)

The full-size v2 build re-instantiates the MPPT UART/RS-485 link that was removed from the mini firmware (see firmware/README.md). The PCB’s J4 footprint is now populated, GPIO 26/27 are now bound to the new MPPT’s comms port, and the firmware’s MPPT loop and charge-controller readback return. The mini build (v2.4) does not have any of this — the Sunapex is standalone.

5.4 Test each sensor

Tools: serial monitor, web browser (Home Assistant)

For each sensor, verify it’s reading sensible values:

IMU: tilt = ~0° when frame is flat, ~35° when tilted
INA219: current = ~0 A when actuator is stationary
DS18B20: temp = ~70-80°F in Phoenix afternoon
Soil moisture: ~30-60% depending on soil wetness
Battery voltage: ~12.0-13.5 V (LiFePO4 range)
Limit switches: HIGH when open, LOW when pressed
MPPT: responds to UART/RS-485 commands (Victron VE.Direct or EPEver Modbus)

Phase 6: Soil and Planting (Day 2-3, ~1 hour)

6.1 Fill the bed with soil

Tools: wheelbarrow, shovel, rake

Process:

Fill the bed with 11.25” of soil (1 cubic yard = 27 cu ft, bed interior is 93” × 41.6” × 11.25” = 30.1 cu ft = 1.1 cu yd).
Use a 50/50 mix of native soil and compost. Or just compost.
Wet the soil to settle it.

6.2 Plant tomatoes

Tools: trowel, tomato seedlings, fertilizer

Process:

Plant 4 tomato seedlings, one in each quadrant of the bed (16” from each wall, evenly spaced).
Use a 6-24-24 starter fertilizer at planting.
Install drip irrigation (optional but recommended for consistent watering).

6.3 Install the grow light (if used)

Tools: drill, screws, 12V LED fixture

Process:

Bolt the grow light fixture to the top of the frame’s east and west cross rails.
Run the 12V switched wire from PCB J5 to the light, through the cable carrier.
Test by toggling the grow light from Home Assistant.

Phase 7: Final Wiring and Validation (Day 3, ~1 hour)

7.1 Connect the solar panel

Tools: MC4 crimper, wire stripper

Process:

Mount the 620W bifacial panel on the frame (already done in Phase 3).
Run the MC4 cables from the panel’s junction box down through the cable carrier to the PCB enclosure.
Splice the panel leads: one leg to the microinverter (240 VAC), one leg to the 30-40 A MPPT (Victron SmartSolar 100/30 or EPEver Tracer 4210AN) input for MPPT battery charging. The MPPT’s VE.Direct / RS-485 port connects to the PCB’s J4 (GPIO 26/27) for telemetry.
The microinverter is its own certified box — install per its instructions.

7.2 Validate the state machine

Tools: serial monitor, web UI

Process:

With everything connected, the firmware should be in FOLDING state (safe default).
Verify the state transitions:
- Send a command to go to NORMAL → frame tilts to 35° via the actuator, IMU reads 35°, INA219 reads 0 A.
- Send a command to go to BEDSUN → frame tilts to 90° (vertical).
- Send a command to go back to FOLDING → frame tilts to 0° (flat).
Check the decision stack:
- Disconnect WiFi → state should still update (offline mode).
- Mock a high-wind NWS forecast → state should go to FOLDING.
- Disconnect the IMU → watchdog should trigger, state should go to FOLDING.

7.3 Test the MPPT

Tools: multimeter

Process:

With the panel exposed to sun, the MPPT should be outputting ~14.4 V to the battery (bulk charge for LiFePO4).
The battery voltage should rise slowly during the day.
Verify the ESP32 can read MPPT telemetry (panel V, panel I, charge state, battery V) over VE.Direct / RS-485 — the new mppt_step loop and sensor.mppt_* entities should populate. Use the ESPHome web UI to verify values.

7.4 Test the DLI grow light

Tools: serial monitor, web UI

Process:

With the panel in NORMAL state, check the DLI reading (mol/m²/day).
If DLI is below target, the grow light should come on.
Verify the light turns on (visually) and the timer limits to 16 hours on / 8 hours off.

Phase 8: Documentation (Day 3, ~30 min)

8.1 Take build photos

Follow the photo template in the README (Build section).

8.2 Log the build

In docs/build_log.md (create it), write:

Date and time of each phase
Any deviations from this guide
Any issues encountered
Photos (with captions)

8.3 Update the README

In the main README, add the build photos to the “Build photos” section.

Build checklist (final, before considering the build “done”)

Build complete. Enjoy the tomatoes and the kWh.