# SP-01 — Assembly

Roughly 45 minutes once everything is printed. Exact mate coordinates are in
`ASSEMBLY-mates.md`; wiring is in `WIRING.md`.

**Do the reservoir leak test first** (`PRINTING.md`). Everything else is easy to
redo; discovering a weeping tank after the electronics are in is not.

## Hardware

| Qty | Item | Where |
|---|---|---|
| 6 | M2 × 8 self-tapping | 4 × Feather, 2 × MOSFET driver |
| 2 | M2.5 × 6 pan-head | soil probe → pot boss |
| 2 | M2.5 × 16 pan-head | light sensor → pilaster standoffs |
| 2 | M3 × 16 self-tapping | pump strap |
| 6 | M3 × 12 self-tapping | enclosure lid |
| 3 | Cable tie, ~2.5 mm wide | strain relief: one at each enclosure lead port, one at the pot pilaster |

Screw lengths were checked against the pilot depth they actually enter — none
bottoms out and none breaks through.

---

## 1. Desk enclosure

**1.1 Boards.** Drop the Feather onto its four standoffs, USB-C facing the wall
opening, and fix with 4 × M2 × 8. The four standoffs are at the Feather's real
hole centres — note the two pairs are *different diameters* (2.5 mm and 2.2 mm);
M2 passes both.

Drop the MOSFET driver onto its two standoffs and fix with 2 × M2 × 8. It only
has two holes in a line, so a third moulded pad sits under the JST end to stop
the board see-sawing — the board should sit flat on all three before you screw
it down.

**1.2 Pump.** Lower the pump into the cradle: the flange goes at the front, into
the slot between the bulkhead and the locating ears; the motor points to the
back. It should drop in with no persuasion and sit still — the bulkhead takes
the flange's front face, the two ears take its side edges, and the rear stop
takes the motor's end plate.

Lay the strap across the top of the pump head and fix with 2 × M3 × 16. The
strap bears on the flat top of the pump head, so tightening it clamps the pump
down onto the cradle rather than bending anything.

> The pump's own flange has no screw holes — that is correct, not an omission.
> It is captured by five faces plus the strap.

**1.3 Tubes.** Push a length of 6 mm OD tube onto each pump port.

- **Suction** (lower port): through the divider pass-through, up the gap beside
  the reservoir, over the tank rim, down to the floor. Fit the strainer (T2) on
  this end.
- **Dose** (upper port): out through the lower round port in the −X wall.

**1.4 Wiring.** Follow `WIRING.md`. Fit C1 (470 µF) and D1 (1N5819) — they are
the difference between a controller that doses reliably and one that resets
every time the pump starts.

**1.5 Close up.** Drop the reservoir into the wet bay, fit the lid with
6 × M3 × 12, and press the fill cap into the port. Refill through the cap; you
only need the lid off to service or clean.

---

## 2. Pot

**2.1 Soil probe.** Feed the probe blade down past the boss on the inside of the
+X wall, so its bare middle section lies flat against the boss face and the JST
connector stays **above** the rim. Fix with 2 × M2.5 × 6 through the probe's own
mounting holes, from inside the pot.

The screws bear on a bare band of the PCB that has no components on either face
— check you are on that band and not over the chip before tightening. Snug, not
hard; it is a 1.6 mm PCB.

**2.2 Light sensor.** Plug the 5-way lead onto the BH1750's header **first** —
the pins point down into the well and are easier to reach now than later. Feed
the lead out through the side channel, tilt the board so its far edge slides
under the retaining lip, then lower it onto the two standoffs and fix with
2 × M2.5 × 16.

The sensor faces the sky with an unobstructed view. It is not waterproof: give
it a thin coat of clear conformal coating if the pot lives outdoors, and do not
pour water over it. The well drains through the side channel.

**2.3 Tether.** Run the 4-wire cable up the +Y spine's groove and the dose tube
up the −Y spine's groove; both snap in. The dose tube pushes into the horizontal
bore that pierces the pot wall — water runs down the inside face, on the
opposite side of the pot from the sensor.

Loop a cable tie through the eyelet post on the +Y spine and around the tether
so a pull on the desk lead is taken by the pot, not the light-sensor header or
the probe JST. Inside the enclosure, do the same at the two lead ports on the
−X wall: each has an eyelet post just inside it — tie the dose tube at the lower
port and the I²C cable at the upper port before you close the lid.

Set the pot into the saucer. It stands on three ribs so it drains freely.

---

## 3. First run

1. Fill the reservoir through the cap.
2. Plug in USB-C. Prime the pump by running it until water reaches the pot —
   if it never arrives, swap the pump leads (see `WIRING.md`).
3. Fill the pot with soil to about 15 mm below the rim. That puts roughly 44 mm
   of the probe blade in the root zone, which is what it is calibrated for.
4. Take a dry reading and a just-watered reading — those two numbers are your
   thresholds. Every soil and pot size reads differently; there is no universal
   value.

Dose little and often. A short pulse every few hours beats a large one once a
day: the soil has time to wick, and you will not flood the saucer.
