Assembly Guide — Dev Platform

Step-by-step build guide for the Plant Caravan dev platform.

Prerequisites

• All components from bom.md
• USB-C cable
• Computer with ESPHome CLI or dashboard
• Soldering iron (optional — only needed for custom cable lengths)

If you are printing your own enclosure

Before assembly, download and print the three enclosure parts listed in /docs/open-source-hardware-print-files:

• enclosure_base.stl
• sensor_mount_lid.stl
• sensor_retainer_frame.stl

Finished dev platform assembly photo

Step 1: Seat the ESP32 Supermini

1. Orient the carrier board with the battery/power connector at the bottom
2. Align the ESP32-C3 Supermini male header pins with the green female socket in the center
3. Press firmly until fully seated — USB-C port faces the top of the carrier

Verify: USB-C port accessible at top. Onboard blue LED (GPIO8) visible through the socket.

Step 2: Connect I2C Sensors

ESP32-C3 only supports 1 hardware I2C bus. All I2C sensors must share GPIO4 (SDA) and GPIO5 (SCL). Use a DIY dupont Y-splitter cable to connect multiple sensors in parallel.

I2C Y-Splitter Cable

Make a 4-wire splitter cable using dupont connectors. Each line (SDA, SCL, VCC, GND) splits from one carrier pin to multiple sensor pins.

                         ┌──► SCD41 SDA
  Carrier pin 4 (SDA) ───┼──► BH1750 SDA
                         └──► [future sensor]

                         ┌──► SCD41 SCL
  Carrier pin 5 (SCL) ───┼──► BH1750 SCL
                         └──► [future sensor]

                         ┌──► SCD41 VDD
  Carrier 3.3V (red) ────┼──► BH1750 VCC
                         └──► [future sensor]

                         ┌──► SCD41 GND
  Carrier GND (black) ───┼──► BH1750 GND
                         └──► [future sensor]

I2C Wiring Table

Making the Y-Splitter

1. Take 4 dupont F-F wires (one per signal: SDA, SCL, VCC, GND)
2. Strip the middle of each wire and solder additional female ends to branch to each sensor
3. Or crimp multiple female connectors onto a single wire
4. Heat shrink the splice points for durability

Power Rail Wire Colors

Warning: The carrier board power rail uses non-standard colors:

Blue = 5V and Red = 3.3V is the opposite of common convention. Double-check before connecting sensors.

Step 2b: Connect Battery (Optional)

The carrier board supports a 3.7V LiPo battery via the B+/B- solder pads (or JST connector) at the bottom of the board. USB charges the battery; battery powers the board when USB is disconnected.

WARNING: The B+/B- silkscreen labels on the bottom of the carrier board are reversed on some units. The pad marked B+ may actually be B-, and vice versa. This has been confirmed on at least one production board (PLC-OX-BF30). Reversed polarity will destroy the charging IC instantly.

Always verify polarity with a multimeter before connecting a battery:

1. Power the board via USB
2. Set multimeter to DC voltage
3. Probe the B+ and B- pads — B+ should read ~4.2V relative to B-
4. If the reading is negative, the silkscreen is reversed — swap your battery wires accordingly

Battery Voltage Monitoring (Optional)

To monitor battery charge level, wire a resistor divider from the verified B+ pad to GPIO4 (ADC1_CH3, freed up since I2C moved to GPIO5/GPIO6):

1. Solder a 100kΩ resistor from B+ pad to left-side signal pin 4 (GPIO4)
2. Solder a 100kΩ resistor from left-side signal pin 4 (GPIO4) to GND
3. Add the battery voltage sensor to the ESPHome firmware

See ESP32-C3 SuperMini Expansion Board docs for firmware configuration and voltage-to-percentage mapping.

The carrier board's charging IC does not expose a current sense pin, so direct solar charge rate measurement is not possible without additional hardware. However, the firmware can infer charging state from voltage trends — see the expansion board docs for a software-only charge trend sensor.

Step 3: Connect Soil Probes

The left-side servo groups make soil probe wiring straightforward — each group has Signal (yellow) + VCC (red) + GND (black) in one row.

Each soil probe connects with 3 F-F dupont wires to its respective left-side servo group.

Do not use left-side group 0 (GPIO0) — boot strapping pin with ADC interference.

Step 4: Power Control (Optional)

To enable soil sensor power switching (saves power, reduces ADC noise when not reading):

1. Wire an N-MOSFET (2N7002) gate to right-side signal pin 6 (GPIO6)
2. MOSFET drain connects to soil probe VCC lines
3. MOSFET source connects to GND

Do not use GPIO8 — it's hardwired to the Supermini's onboard LED.

Step 5: Flash Firmware

1. Connect USB-C cable to ESP32 Supermini
2. Flash ESPHome config:

   esphome run plant-monitor.yaml

3. See hardware/firmware/ for firmware configuration
4. Choose a telemetry target: /docs/observability-platform documents the current Plant Caravan hosted InfluxDB path, self-hosted InfluxDB path, and Prometheus scrape path.

Step 6: Verify

After flashing, confirm all sensors report in Home Assistant or ESPHome logs:

Troubleshooting