Hardware Build

Hardware Build

End-to-end guide: from "the BOM has arrived" to "powered-on hub + tank."

The deep reference (schematics, pin maps, BOM, 3D STEP files) lives in the repo's hardware/ folder. This wiki page is the step-by-step tour.

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What you'll have at the end

• A hub (RX) plugged into a USB-C wall adapter, indoors, ~15 cm × ~10 cm × ~5 cm.
• One or more transmitters (TX), each mounted on the lid of a tank, solar-powered.
• Sensor cables going from each TX's enclosure down through its tank lid (field-cut to length).

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Build order

1. Print the enclosures

Files: hardware/cases/circular-v1/ (TX) + your own hub case (we don't ship one yet — community designs welcome).

PETG, 0.2 mm, 30 % gyroid infill, 4 perimeters, ~80 °C bed, ~245 °C nozzle. Print supports for the top-with-solar piece (tree). See cases/README.md for full notes.

While prints are running, order PCBs.

2. Order PCBs

Send the schematic SVG + project files to JLCPCB or PCBWay. 10 pieces is the minimum and works out to ~₹60 each. The PCBs arrive in ~10 days (express ~5).

We have a stretch-goal of publishing the EasyEDA project files publicly. For now, the schematic PNG/SVG + pin assignments are enough to recreate the design — see Wiring Reference (Hub) and Wiring Reference (Transmitter).

3. Order parts

Use the Bill of Materials. Order 2× of everything, because the first one is the build, the second is the spare. SMD parts are cheap when you buy in bulk; the savings disappear if you have to re-order.

4. Hand-solder the PCBs

The PCBs are designed to be hand-solderable — no QFNs, no fine-pitch BGAs. SMD passives are 0805 / 0603 (manageable with a fine tip and tweezers). Use leaded solder if you're new to it; lead-free is harder.

Order of soldering:

• SMD passives (resistors, caps, diodes) first — easiest while the board is empty.
• THT (through-hole) buttons + screw terminals next.
• Modules (ESP32 module, RYLR998, INA219, MT3608, CN3791) last — they sit on female headers so you can pull them for debugging.

Test each subsystem before populating the next:

1. Power chain — solder power section, plug in 18650, scope 3.3 V rail with a meter.
2. UART — plug in RYLR998, power on, send AT\r\n via your USB-UART adapter. Expect +OK\r\n.
3. I²C — plug in INA219, i2cdetect (over USB serial) finds 0x40.
4. Sensor — wire JSN-SR04T (5 V power, TRIG/ECHO with divider), check idf.py monitor shows distance values.

5. Flash the firmware

Easiest path: use the browser flasher.

For development: install ESP-IDF v5.5.2, then:

# Hub
cd firmware/Receiver-ESP32-DevKit
idf.py set-target esp32
idf.py build flash monitor

# Transmitter
cd firmware/Transmitter-IDF
idf.py set-target esp32c3
idf.py build flash monitor

The VERSION file in each firmware folder is the single source of truth — edit it once to bump versions.

6. Assemble each enclosure

Per cases/circular-v1/README.md:

1. Heat-set M3 inserts into the four corners of the base (if using).
2. Drop the populated PCB in, secure with the 18650 holder.
3. Feed the sensor cable through the gland from outside; screw-terminal both ends.
4. Mount the panel in the lid pocket; feed wires through the grommet; solder to PCB.
5. Lay the EPDM gasket on the base rim; screw the lid down with 4× M3 stainless to moderate torque.

7. Mount on the tank lid

• Field-drill a hole in the tank lid for the BSP sensor-screw boss.
• Thread the boss through the lid from above. Tighten the nut from underneath. Teflon tape on threads for water seal.
• Sit the enclosure on the lid (solar panel facing the sun). Use M3 stainless screws if you want it fixed.
• Run the sensor cable from the enclosure's cable gland to the sensor-screw boss; screw-terminal both ends.
• The JSN-SR04T transducer head ends up ~20 mm below the lid's internal surface, pointing down at the water.

8. Power on, pair, verify

• Hub gets USB-C power. Setup mode → Wi-Fi config → MQTT config (cloud or local).
• TX gets solar + 18650. Hold BOOT 5 s → pairing.
• Confirm in the PWA / web UI.

See First Boot for what every step should look like.

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Photos of a finished build

The TX board, fresh from the fab, ready to populate:

After hand-soldering — modules sitting on female headers so you can pull them for debugging:

Back of the same board (passives + the inline Schottky on the battery rail):

Angled view showing the whole module stack:

Lid half with the solar panel installed in the integrated pocket:

Closed assembly side profile — gasket compressed, ready to mount:

The BSP-threaded sensor mount installed in a test tank lid:

Close-up of the sensor-screw boss + the locking nut from inside the tank:

Opened unit showing internal layout + the SMA antenna routing (optional external antenna variant):

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"I broke something"

Almost every first build hits one of these:

• No 3.3 V at the boost output → MT3608 trim-pot. Adjust with a tiny screwdriver while measuring with a meter.
• RYLR998 doesn't +OK → reversed UART. Try swapping.
• Sensor reads zero → ECHO divider wrong polarity, or sensor is in UART mode (R19/R27 solder pads). See Troubleshooting.
• 18650 reads 0 V → reversed cell. The inline Schottky saves the board; reseat the cell.
• OLED is blank → I²C address wrong (0x3D vs 0x3C), or SDA/SCL crossed.

For anything else, open an issue with a photo of the board and the idf.py monitor log.