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SunSprout Satellite

Differential I2C Sensor Leaf Node

The SunSprout Satellite is the dedicated remote sensor endpoint for the SunSprout ecosystem. It terminates a long differential-I2C cable run from the SunSprout Hub, restores standard local I2C signaling, and monitors up to four capacitive soil-moisture probes plus a 1-Wire soil-temperature probe.

SunSprout Satellite 3D top render hero image

What is the Satellite?​

The SunSprout Satellite functions as a remote garden/agricultural probe station. Where standard I2C buses degrade after a few tens of centimetres, the Satellite connects to the Hub over standard Category-rated twisted-pair patch cable (up to 20+ metres) using differential signaling.

At the endpoint, the board translates the differential clock and data signals back into standard 3.3V single-ended I2C, hosts an onboard 16-bit analog-to-digital converter (ADS1115) and a hardware 1-Wire master bridge (DS2482-100+), and distributes power and ground to local sensors.

SunSprout Satellite 3D bottom render

Physical Specifications​

PropertyValueNotes
Form factor27.25 × 51.10 mmSlender rectangular profile fits small waterproof enclosures or conduit
Board thickness1.6 mmStandard FR4
Layer stackup4 copper layersF.Cu (signals), In1.Cu (power), In2.Cu (ground plane), B.Cu (signals)
Mounting3× M2 non-plated holes3.0 mm corner inset at top; 1 mid-board support hole
Primary interface1× Amphenol RJHSE53808P8C (RJ45) jack with metal EMI shield
Sensor ports5× JST PH 2.0mm 3-pin4 moisture probe inputs + 1 temperature probe input
Auxiliary port1× 2.54mm 4-pin headerSecondary power injection / tap header (VCC_2, GND_2, GND, SAT_3V3)

Capabilities & Architecture​

1. Differential I2C Bus Endpoint (PCA9615)​

  • PCA9615DPZ differential buffer translates DSCL+/DSCL- and DSDA+/DSDA- back into local SCL_LOCAL and SDA_LOCAL.
  • Fixed Onboard Termination: Populated with matched resistor ladders (390Ω bias pull-ups to SAT_3V3, 100Ω line matching resistors, and 390Ω bias pull-downs to GND) across both differential pairs. This ensures proper transmission line termination without loose plug-in resistors.
  • TVS / ESD Protection: An onboard USBLC6-4SC6 transient voltage suppressor array clamps all four differential lines against outdoor static and handling discharge.

2. High-Precision Soil Moisture Monitoring (ADS1115)​

  • ADS1115IDGS 16-bit 4-channel delta-sigma ADC with programmable gain amplifier and internal reference.
  • Reads analog voltage outputs from up to four independent capacitive soil-moisture probes (e.g., DFRobot SEN0193 / Gravity interface).
  • Four 3-pin vertical JST PH connectors (J2–J5) distribute GND, SAT_3V3, and signal lines (MOIST1–MOIST4).
  • Configurable I2C Address (JP1): 4-way solder jumper on the bottom side selects addresses 0x48, 0x49, 0x4A, or 0x4B (0x48 default bridged).

3. Dedicated 1-Wire Temperature Bridge (DS2482-100+)​

  • Hardware I2C-to-1-Wire master bridge eliminates software bit-banging and timing jitter over long probe leads.
  • Dedicated 3-pin vertical JST PH connector (J6) connects a waterproof DS18B20 digital temperature probe (SAT_3V3, GND, ONEWIRE_DQ).
  • Onboard 4.7kΩ pull-up to SAT_3V3 provides reliable bus drive.
  • Configurable I2C Address (JP16): Dual solder jumper selects address bits AD0 and AD1 (default: 0x18).

4. Power & Auxiliary Flexibility​

  • Zero Local Regulator Overhead: Designed to operate directly from SAT_3V3 delivered by the Hub over conductor 4 (VCC_1). At typical cable lengths (under 20 m) and satellite currents (~15–25 mA), round-trip IR drop is negligible (~0.1–0.2 V).
  • Decoupling & Reservoir: An onboard 22 µF bulk capacitor (C1) buffers cable transients, accompanied by dedicated 100 nF high-frequency ceramic decoupling capacitors directly adjacent to every active IC pin.
  • Auxiliary Power Path (J7, JP14, JP15):
    • VCC_2 (conductor 3) and GND_2 (conductor 6) pass directly to header J7.
    • Solder jumper JP14 allows rerouting the satellite's power feed from VCC_1 to VCC_2.
    • Cuttable jumper JP15 permits isolating GND_2 from system GND.
  • Single-Cut Pull-Up Jumper (JP11): A custom 3-pad solder jumper with a single collinear cut channel allows disconnecting both local 4.7kΩ I2C pull-ups simultaneously with a single craft knife slice.
  • Cable Shield Isolation (JP13): Cuttable solder jumper on the bottom side connects the RJ45 metal shield to system ground by default, allowing single-point grounding configurations when required.

Further Reading​

  • Dimensions & Mounting — Exact outline, mounting hole locations, connector courtyard extents, and enclosure clearance guidance.
  • Hub Overview — Main system controller, solar MPPT charger, and differential I2C driver.
  • Design Files — Schematic PDFs, Gerbers, and 3D CAD STEP models.