The steps below are a summary; the full guide with wiring table, drill sizes, printer settings and troubleshooting is instruction.md in the repository.

1. Print the case. Base floor-down and cover upside down, both without supports. Check the banana socket thread and the switch hole against your parts before printing.
2. Make the PCB. Print KiCAD/toner_B.Cu_1to1.pdf at 100 %, not mirrored, and check the 90 × 66 mm outline with a ruler. Transfer, etch and drill (0.8 / 1.0 / 1.1 / 2.2 / 3.2 mm). Optional: UV solder mask using the two mask copies on page 3 and the printed jig. Or order the board from the Gerbers.
3. Solder the board, low parts first: resistors, D1 (band on the "K" pad), DIP-8 socket (leave U2 out), 100 nF caps, trimmer, 78L05 (pin 1 = OUTPUT, reversed vs a 7805), 10 µF caps (+ on the square pad), JST connectors, heatsink.
4. Mount the LM317 on the heatsink with the insulating kit — its tab is live. Check with a multimeter that the heatsink and the tab read open, then solder the legs. Trim all leads to 3 mm or less.
5. Fit the panel parts: ZK-4KX snaps into the front, then the switch, banana sockets and DC jack.
6. Wire it: jack + → switch → ZK-4KX IN+ and board J1; jack − → ZK-4KX IN− and J1; ZK-4KX OUT+/OUT− → red/black sockets. Use 0.75–1 mm² wire for the power path. Never connect OUT− to IN−.
7. Fix the LM35 flat against the ZK-4KX heatsink with thermal paste and Kapton, legs insulated, and wire it to J2. Measure the heatsink voltage first: it may not be at ground.
8. First power-up, U2 out and fan unplugged: check about 5 V on U2 socket pin 8. Power off, insert U2, plug in the fan and the LM35. At room temperature the fan should stay still (about 1.25 V on it).
9. Mount the board and fan: board on 6 mm standoffs with M3 screws, fan on the left wall, then glue the magnets into the base and cover (mind the polarity).
10. Calibrate: measure U2 pin 7 and turn the trimmer until V_REF [mV] = 11 × T_start − 155 — for example 285 mV for a fan that starts at 40 °C. The trimmer can be reached through a hole in the lid.