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Wattplot Mini v2.4 — Build Guide

STALE — written for the v2.4 / ESP32-C3 + BMI160 IMU + relay + GPIO4/5/10 architecture. Pin numbers, sensor names, and entity IDs in this doc do not match firmware/wattplot.yaml v3.2 (ESP32-S3, DRV8871 for solenoid, GPIO6/7/10/12/16). The Mini’s physical build is still described accurately here (bed, panel, kickstand actuator), but the electronics steps (Phase 6 onward) need cross-checking 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.

Benchtop design-validation prototype. 18”×14” bed, ECO-WORTHY 10W panel, 100mm kickstand linear actuator — sized to match the parts you already ordered.

Tilt range: 0-35° (limited by the kickstand geometry; matches the power-optimal range per the Phoenix sun sim).

Build time: ~3-4 hours Build cost: ~$193 (new parts: Sunapex 10A MPPT, sensors, lumber, hardware, solenoid watering). Already have: $50 (battery, ESP32, actuator, panel).

Phase 0: Order parts (Day 0, ~30 min)

Already ordered (Saturday)

Still need to order (one-stop)

Lumber (all PT DF, all from 8ft stock)

If pre-cut at the lumber yard:

Total lumber cost: ~$19

Phase 1: Bed (Day 1, ~1 hour)

1.1 Cut the half-lap notches

Each bed wall has a 1.5” wide × 0.375” deep notch at each end.

Tools: circular saw, chisel, mallet, square

Process:

  1. Mark the notch location on each wall (1.5” from each end, 0.375” deep).
  2. Make multiple passes with the circular saw at the notch depth (don’t try to cut 0.375” deep in one pass).
  3. Clean out the waste with a chisel.
  4. Test-fit two walls at a corner.

Verification: the two walls meet at a 90° corner with no daylight.

1.2 Assemble the bed box

Tools: drill, ⅛” pilot bit, #6 × 1.5” wood screws, square

The bed is small (18”×14”), so the joints don’t need to be as beefy as the full-size. Use #6 × 1.5” wood screws (instead of #8 × 2” for the bigger builds).

Process:

  1. Lay out the 4 walls on a flat surface.
  2. Bring the corners together. The half-lap notches interlock.
  3. Pre-drill 2 holes per corner (one near the top, one near the bottom).
  4. Drive #6 × 1.5” wood screws through the corners.

Verification: bed box is 18” × 14” outside, square (measure diagonally — both diagonals should be the same length).

1.3 Attach the skids

Tools: drill, ⅛” pilot bit, #6 × 1.5” screws

Process:

  1. Flip the bed upside down.
  2. Place two 1x2x18” skids under the bed, aligned with the long walls.
  3. Pre-drill and screw through the skids into the bed walls.
  4. Use 2-3 screws per skid.

Verification: skids are flush with the bed ends, square, and the whole bed sits level on the ground.

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

2.1 Assemble the frame rectangle

Tools: drill, ⅛” pilot bit, #6 × 1.5” wood screws, square

Process:

  1. Lay the 4 frame rails (2 long + 2 cross) on a flat surface.
  2. The cross rails fit between the long rails. Butt joints (no miter).
  3. Pre-drill 2 holes per corner (through the cross rail into the long rail end). Use 2 screws per corner.
  4. Drive #6 × 1.5” wood screws.

Verification: frame is square, 18” × 14” outside, 16.5” × 12.5” inside.

2.2 Add the diagonal brace

Tools: drill, ⅛” pilot bit, #6 × 1” screws, measuring tape

Process:

  1. The 2x4x21” diagonal brace runs corner to corner inside the frame.
  2. Position the brace so its ends butt into the inside faces of the long rails (square ends, no miter).
  3. Pre-drill 2 holes per end (through the brace into the long rail inside face).
  4. Drive #6 × 1” screws (4 screws total, 2 per end).

Verification: brace is at the diagonal angle (~37°), both ends screwed.

2.3 Install hinges on the bed’s south wall

Tools: drill, 5/64” bit (for hinge screws), screws (the small butt hinges come with their own screws), measuring tape

Process:

  1. Lay the frame on top of the bed, with the frame’s south rail resting on the bed’s south wall.
  2. Position the 2 hinges evenly along the south rail: spacing 13”, centered (2.5” margin on each end of the 18” rail).
  3. Mark the hinge positions on both the frame’s south rail and the bed’s south wall.
  4. Pre-drill 4 holes per hinge (2 per leaf), 5/64” bit.
  5. Attach the wall leaf to the bed’s south wall.
  6. Attach the frame leaf to the frame’s south rail.
  7. The frame should now hinge freely.

Verification: frame hinges smoothly between 0° and ~35° tilt. The ⅜” hinge pin holes in both hinges are aligned (the continuous pin passes through both).

2.4 Insert the continuous hinge pin

Tools: mallet (rubber), ⅜” drill bit (if pin is too tight)

Process:

  1. Thread the ⅜” × 22” steel rod through both hinges, starting from one end.
  2. Tap gently with a rubber mallet to seat the pin fully.
  3. The pin should extend ~1” past the last hinge on each end.

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

Phase 3: Panel (Day 1, ~10 min)

3.1 Sizing note (important!)

The 10W panel (13.3” × 8.1”) is smaller than the frame’s interior (16.5” × 12.5”). The panel sits inside the frame interior with margin on all four sides:

The mid-clamps grip the panel frame at the rail positions, holding the panel firmly. This is the inverse of the v2.1 design (where the panel overhung the frame) — for the small 10W panel, it fits comfortably inside the frame.

3.2 Lift the panel onto the frame

Tools: hands (10W panel is only 1.88 lb)

Process:

  1. With the frame flat on the bed, place the 10W panel on top of the frame, centered.
  2. The panel’s aluminum frame should rest on the wood rails.

Verification: panel is centered, with even margin on all four sides.

3.3 Clamp the panel to the frame

Tools: drill, M8 hex driver, 1” mid-clamps

Process:

  1. Place 2 mid-clamps per long rail (4 total), at positions ±4” from the panel center.
  2. Tighten the M8 bolts to clamp the panel frame to the wood rails.
  3. Torque to ~3 Nm (snug, not crushing — the small panel frame is fragile).

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

3.4 Install the kickstand TOP mount bracket

Tools: drill, ⅛” pilot bit, #6 × 1.5” wood screws

Process:

  1. Cut a 3” length of 1x2 (offcut from any 1x2 scrap).
  2. Position the bracket on the underside of the panel, 2 inches north of the south edge of the panel.
  3. The bracket should be flush with the panel’s south frame edge (in z direction), and sit just below the panel’s underside (panel underside is at y=4.75, bracket top is at y=4.75, bracket bottom is at y=4.0).
  4. Attach the bracket to the panel’s aluminum frame, not the bed. The bracket moves WITH the panel as the panel tilts.
  5. Pre-drill 2 holes through the bracket’s top face into the panel frame’s channel.
  6. Drive #6 × 1.5” wood screws.

Verification: the bracket hangs from the panel’s underside, 2” north of the south edge. The bracket moves up/down as you manually tilt the panel.

Phase 4: Kickstand Actuator Mount (Day 1, ~20 min)

4.1 Mount the bottom block on the bed’s south wall

Tools: drill, ⅛” pilot bit, #6 × 1.5” wood screws

Process:

  1. Cut a 3” length of 1x2 (offcut from any 1x2 scrap).
  2. Mount the block on the outer face of the bed’s south wall, at the bottom (resting on the ground or on the skid).
  3. Position: y=0 to 0.75 (ground to top of skid), z=+7 to +7.75 (outer face of south wall + 1x2 extending out), x=-1.5 to +1.5 (centered along bed length).
  4. Pre-drill 2 holes and drive #6 × 1.5” screws through the block into the bed’s south wall.

Verification: block is firmly attached to the bed’s south wall, low.

4.2 Insert the bottom pin

Tools: ⅜” clevis pin, rubber mallet

Process:

  1. The bottom pin is a ⅜” × 3.5” steel pin that goes through the bottom block, perpendicular to the actuator’s axis (i.e., along the X axis, parallel to the bed length).
  2. Drill a ⅜” hole through the block (centered, 0.375” above the block’s bottom and 0.75” outside the wall’s outer face).
  3. Insert the pin through the hole. The pin should extend ~0.25” past each side of the block.

Verification: pin is in place, sticking out both sides of the block.

4.3 Mount the kickstand actuator between the pins

Tools: ⅜” clevis pin + cotter pin, rubber mallet

Process:

  1. The 100mm (3.94”) stroke 12V 70N (15.7 lbf) linear actuator has a ⅜” clevis pin hole on each end (body side and rod side).
  2. Pin the body-side clevis to the bottom pin (on the bed’s south wall, low position).
  3. Pin the rod-side clevis to the top pin (on the panel’s underside bracket).
  4. Use cotter pins to keep the clevis pins from sliding out.

Geometry check: at 0° panel tilt, the actuator is at its collapsed length (~5” between pin centers). When the panel tilts up, the top pin moves up and inward, and the actuator extends by ~0.7” to reach the 35° tilt position.

Verification: actuator is pinned at both ends. Manually extend and retract the rod — the panel should tilt up and down. Test the range:

If the panel binds before reaching 35°, the actuator’s top bracket may need to be repositioned. If the actuator doesn’t have enough stroke, you’ve hit the geometry limit.

Phase 5: Sensors and Wiring (Day 1, ~45 min)

5.1 Install the IMU on the frame

Follow the same principle as the full-size build (see docs/sensor_placement.md § 1): mount the BMI160 breakout on the underside of the frame’s north rail, centered, with the X axis along the bed’s long axis.

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

5.2 Install the soil sensors

If using the bed for plants:

5.3 Mount the breadboard

For the mini, you can use a breadboard or perfboard for the ESP32 circuit instead of the full-size PCB. Mount the breadboard on the bed’s east short wall, near the battery.

Tools: #4 wood screws, double-sided tape (alternative)

5.4 Wire the breadboard

Follow docs/wiring.md (the same wiring works for the mini, just with shorter cables).

Tools: jumper wires, wire stripper, multimeter

5.5 Continuity check

Before applying power, verify:

Phase 6: Battery and First Power-On (Day 1, ~20 min)

6.1 Connect the battery

Tools: multimeter, 3A fuse

For the mini (small 10W panel), use a 3A fuse (the actuator stall current is well below this).

Process:

  1. Place the 12V 7Ah LiFePO4 battery next to the bed.
  2. Connect the battery negative to the breadboard’s ground bus.
  3. Connect the battery positive through a 3A fuse, then to the 12V rail on the breadboard.
  4. Do not install the fuse yet.

6.2 Install the fuse and power on

Process:

  1. Connect the laptop via USB to the ESP32.
  2. Install the fuse.
  3. The ESP32 should boot. The status LED should light up.
  4. Flash the firmware: esphome run firmware/wattplot.yaml.

6.3 Verify boot

Process:

  1. Open the serial monitor (115200 baud).
  2. Look for ESPHome boot messages. Verify:
    • “Wattplot Controller” branding
    • IMU detected
    • State: FOLDING (safe default)

Note: the v2.4 firmware does not connect to a charge controller over UART — the Sunapex is a standalone waterproof MPPT. There is no “DPS5005 detected” line anymore.

6.4 Configure max tilt

The firmware should be configured to cap tilt at 35° (the kickstand’s mechanical limit). Set this in the ESPHome globals:

globals:
  - id: max_tilt_deg
    type: float
    initial_value: '35.0'

6.5 Test each sensor

For each sensor, verify it’s reading sensible values (see docs/test_checklist.md Phase A for the full list).

Phase 7: Solar Panel and Sunapex MPPT (Day 1-2, ~20 min)

7.1 Connect the solar panel

Tools: wire stripper, #1 Phillips, heat-shrink (if cutting SAE leads)

Process:

  1. The 10W panel has MC4 connectors on the back. The Sunapex 10A MPPT ships with SAE connectors on both sides and a polarity reversal adapter — connect the panel’s MC4 directly to the Sunapex’s included SAE adapter. No MC4 crimper or pigtails needed.
  2. Mount the Sunapex 10A MPPT on the bed’s east wall (next to the PCB enclosure). The Sunapex is IP67 — no separate enclosure needed, but mount it under the panel edge so the grommet for the panel cables can enter the bed wall close by.
  3. The Sunapex’s battery lead comes with an SAE connector on the controller end and bare wire on the other. Either cut the SAE end off and crimp ring terminals, or buy a separate SAE-to-bare-wire pigtail. Run 14 AWG from the Sunapex BAT+ through a 3 A in-line fuse (within 6” of the battery +) to battery +.
  4. Run 14 AWG from the Sunapex BAT− to battery −.

7.2 Power up the Sunapex

Process:

  1. Connect the battery first (BAT+ and BAT−). The Sunapex is powered by the battery, not the panel. Its LCD should light up.
  2. Press the MODE button on the Sunapex until the LCD shows the LiFePO4 chemistry mode (usually labelled “Li” or “LiFePO4” — depends on firmware rev). Default out-of-box is sometimes sealed lead-acid.
  3. Connect the panel MC4 to the Sunapex PV input via the included SAE adapter. The Sunapex will detect PV and start charging; the charging LED should come on.

7.3 Test the MPPT

Process:

  1. With the panel in sun, the Sunapex should be in bulk charge (charging LED on, LCD shows ~14.4 V output to the battery).
  2. Watch the battery voltage rise slowly during the day on the ESPHome sensor.battery_voltage entity. The Sunapex will hold at ~14.4 V during bulk, drop to absorption, then ~13.4 V float once full.
  3. Expected power: 8-9 W peak at noon in full sun (after 15% derate for the 10 W panel and ~96% MPPT efficiency).
  4. Verify sensor.panel_power_w reads roughly the same as the Sunapex is pushing into the battery (within ~0.5 W — the small difference is the INA219 shunt tolerance and the Sunapex’s own ~6 mA quiescent draw).

Phase 8: Soil and Planting (Day 2, ~10 min)

8.1 Fill the bed with soil

Process:

  1. Fill the bed with 4” of soil (interior 16.5” × 12.5” × 4” = 0.48 cu ft, ~3.5 gallons).
  2. Use a potting mix (not native soil — too heavy for a small planter).

8.2 Plant something

Process:

  1. Plant 1 small herb (basil, parsley) or a small flower.
  2. Use a starter fertilizer.

Phase 9: Test and Validate (Day 2, ongoing)

9.1 Bench test (1 week)

Run the mini on your workbench for a week. Monitor:

9.2 What to learn from the mini

After a week, you’ll know:

If the mini works for a week, the full-size build will work too. Apply any tuning you discovered (Kp, Ki, deadband, target_current) to the full-size firmware.

Phase 10: Watering System (solenoid on tap) (Day 2, ~45 min)

The mini v2.4 is a smart planter: it reads soil moisture + temps, decides when to water, and energizes a 12V solenoid to drip-feed the bed from your house’s cold water tap. No pump, no reservoir, no refilling. The full design spec is in docs/watering.md.

10.1 Tee into the cold water supply

Tools: adjustable wrench, tube cutter (or hacksaw), Teflon tape

Process:

  1. Pick your tie-in point. The easiest options are:
    • Outdoor hose bib (e.g. on a patio wall): screw a 1/4” barb adapter directly into the faucet spout
    • Under-sink cold water line: cut the 3/8” or 1/2” copper pipe, install a 1/4” tee, restore flow
  2. Shut off the water first. Open the closest faucet to drain residual pressure.
  3. Cut the pipe (or unscrew the hose bib spout if going that route).
  4. Wrap the tee threads with 2-3 layers of Teflon tape, install the tee, hand-tighten, then snug with the wrench (don’t over-torque on plastic fittings).
  5. Restore water pressure and check for leaks. Wait 5 minutes, check again.
  6. Attach a 1/4” barb to the tee’s 1/4” outlet.

Verification: no leaks at the tee after 5 min under pressure.

10.2 Run the supply line to the bed

Tools: scissors, 1/4” tubing cutter (or sharp knife)

Process:

  1. Cut a length of 1/4” vinyl tubing (typically 5-20 ft depending on the run from tee to bed).
  2. Push one end onto the tee’s 1/4” barb.
  3. Route the tubing from the tee to the bed (along the wall, across the floor, up to the workbench level). Use zip ties every 2-3 ft to keep it tidy.
  4. (Optional) Install a 5-30 PSI pressure regulator in the line, set to ~15 PSI for the drip emitter. Not strictly required if your emitter is rated for full house pressure (40-80 PSI), but it gives you a more consistent flow rate.
  5. Leave the other end of the supply line at the bed, ready to connect to the solenoid inlet.

Verification: briefly open the upstream valve (or unscrew the supply tubing from where the solenoid will go) and confirm water flows. Reconnect and leave the system pressurized but the solenoid closed.

10.3 Mount the solenoid

Tools: screwdriver, drill, zip ties (or screws)

Process:

  1. Mount the 12V DC normally-closed solenoid valve on the bed’s east short wall, at ~6” height (above any potential splash zone). Zip-tie it to the bed’s frame, or screw it to a small block of 1x2 first and then screw the block to the bed wall.
  2. The solenoid has a flow direction arrow — make sure INLET faces the supply tubing, OUTLET faces the drip line.
  3. Connect the supply tubing to the solenoid INLET.
  4. Cut ~3-4 ft of 1/4” tubing, connect to the solenoid OUTLET, run it to the bed’s soil surface.
  5. Attach a pressure-compensating drip emitter (2 GPH) to the other end, insert the emitter 1” deep into the soil near the plant.

Verification: with the solenoid DE-energized (no relay trigger), no water should flow (NC = normally closed). With the relay on manually, water should drip from the emitter at ~2 mL/sec.

10.4 Wire the relay and solenoid

Tools: wire stripper, small screwdriver (for relay terminals)

Process:

  1. Mount the 1-channel relay module on the bed’s east short wall, near the breadboard.
  2. Connect:
    • Battery 12V+ → relay COM terminal
    • Relay NO (normally open) → solenoid + (red wire)
    • Solenoid - (black wire) → battery 12V- (GND bus)
    • Relay VCC → ESP32 5V (or 3.3V, depending on relay module)
    • Relay GND → ESP32 GND
    • Relay IN → ESP32 GPIO 5
  3. Test: in Home Assistant, toggle switch.watering_solenoid ON for 10 seconds. Solenoid should click open, water should flow, then auto-stop at the 30-second watchdog.

Important: if the solenoid wires are reversed, no harm done (it’s a DC coil, not polarized), but the flow direction arrow on the body MUST be correct — reversed flow will leak through the diaphragm when closed.

10.5 Install the temperature + soil moisture sensors

Tools: wire stripper, small screwdriver, thermal tape (or zip ties)

Process (DS18B20 sensors, all on the same 1-Wire bus on GPIO 10):

  1. Panel temp: attach a DS18B20 to the back of the panel with thermal tape. Route the wire along the panel edge to the bed’s hinge area, then to the breadboard.
  2. Soil temp: bury a DS18B20 2” deep in the soil (next to the soil moisture sensor).
  3. Battery temp: tape a DS18B20 to the side of the battery with Kapton tape (handles the heat).
  4. All 3 sensors share VCC (3.3V), GND, and the data line (GPIO 10) with a single 4.7kΩ pullup resistor.
  5. Soil moisture: Insert the Stemedu V1.2 capacitive sensor 2” deep into the bed soil, near the center. Connect: VCC → 3.3V, GND → GND, AOUT → ESP32 GPIO 4 (ADC).

Verification: in Home Assistant, verify all 4 sensors show reasonable values (panel ~20-40°C, soil ~15-30°C, battery ~15-30°C, moisture 30-60%).

10.6 Verify energy + SOC + POA monitoring

Process:

  1. The INA219 (panel V/I), Sunapex (charge status, visible on its own LCD), and BMI160 (tilt) are already wired from Phase 5. The Sunapex does not export telemetry to the ESP32, so charge state is read from the Sunapex’s own LCD. Verify these entities in HA:
    • sensor.panel_voltage_v (should read ~17-21V in sun)
    • sensor.panel_current_a (should read 0-0.58A in sun)
    • sensor.panel_power_w (V × I, should peak ~8-10W in full sun)
    • sensor.battery_v (should read ~12-13.6V)
    • sensor.battery_soc_pct (should follow the LiFePO4 curve)
    • sensor.current_tilt_deg (should match panel angle)
    • sensor.poa_irradiance_w_m2 (should peak ~900-1000 W/m² at solar noon on a clear day)
    • sensor.panel_efficiency_pct (should be 12-18% on a good day)
    • sensor.energy_today_kwh (should accumulate ~30-50 Wh/day in good sun, = 0.03-0.05 kWh/day)
    • sensor.energy_total_kwh (lifetime counter)
  2. If poa_irradiance_w_m2 reads 0 or wildly off, check the latitude/longitude in the firmware config (should be 33.45, -112.07 for Phoenix) and the time sync (NTP or manual).
  3. If panel_efficiency_pct reads >20%, the panel area calculation is wrong — double check panel_L_in × panel_W_in in wattplot_params.py.

10.7 Test the watering automation

Process:

  1. In Home Assistant, verify these entities exist:
    • sensor.soil_moisture_pct
    • sensor.panel_temp_c / sensor.soil_temp_c / sensor.battery_temp_c
    • sensor.battery_v / sensor.battery_soc_pct
    • sensor.poa_irradiance_w_m2
    • sensor.energy_today_kwh
    • switch.watering_solenoid (manual toggle)
    • switch.watering_automation (auto mode)
  2. Force a watering event: in HA, set sensor.soil_moisture_pct to 25 (below the 30% threshold), wait 15 seconds. The solenoid should click open for 50 seconds (~100 mL water).
  3. Verify sensor.water_ml_today increments by ~100 mL.
  4. Verify sensor.watering_events_today increments by 1.
  5. Test safety blocks:
    • Set sensor.panel_temp_c to 50°C → watering is blocked
    • Set sensor.battery_v to 11.0V → watering is blocked
    • Set sensor.battery_soc_pct to 15 → watering is blocked
    • At night (panel_power_w < 0.5W) → watering is blocked

Final build checklist

Mini v2.4 complete. A real smart planter with full energy telemetry. Apply learnings to the full-size build.