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 using differential signaling. The PCA9615 datasheet quotes a 3 m cable at full speed, and longer runs at lower clock speeds; long runs have not been tested on this board.

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.

Physical Specifications

Property	Value	Notes
Form factor	27.25 × 51.10 mm	Slender rectangular profile fits small waterproof enclosures or conduit
Board thickness	1.6 mm	Standard FR4
Layer stackup	4 copper layers	Signals on the outer layers; the two inner layers carry ground and power zones
Mounting	3× M2 non-plated holes	3.0 mm corner inset at top; 1 mid-board support hole
Primary interface	1× Amphenol RJHSE5380	8P8C (RJ45) jack with metal EMI shield
Sensor ports	5× JST PH 2.0mm 3-pin	4 moisture probe inputs + 1 temperature probe input
Auxiliary ports	2.54mm headers, plus a Qwiic port	`J7` taps the cable's power and ground pairs, `J9` is the local 3.3V and ground header, and `J8` is a JST SH Qwiic / STEMMA QT port

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 (bias pull-ups to RJ45_VCC_1, line-matching resistors, and bias pull-downs to RJ45_GND_1) 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).
The DS2482's internal pull-up drives the 1-Wire line. A footprint for an optional external 4.7kΩ pull-up (R9) is left unpopulated.
Configurable I2C Address (JP16): Dual solder jumper selects addresses 0x18 (factory default), 0x19, 0x1A, or 0x1B.

4. Power & Auxiliary Flexibility

Decoupled Power Architecture: PCA9615 transceiver power (VDDB), the differential termination bias networks, and the ESD clamp array connect directly to the cable supply nets (RJ45_VCC_1 / RJ45_GND_1). Those nets are joined to the local rails by JP18 and JP17, which are bridged by default.
Bulk Cable Reservoir (C1): An onboard 22 µF bulk capacitor (C1) sits directly across RJ45_VCC_1 and RJ45_GND_1 right at the cable entry, dampening inductive cable ringing and buffering transient load steps. Dedicated 100 nF ceramic decoupling capacitors sit directly adjacent to every active IC pin.
Factory Default Operation (Zero Overhead): Pre-bridged cuttable solder jumpers JP18 (RJ45_VCC_1 $\leftrightarrow$ SAT_3V3) and JP17 (RJ45_GND_1 $\leftrightarrow$ GND) power the board directly from the Hub's regulated 3.3V rail over Pair 1 out of the box with zero external wiring.
Cable Power Breakout Header (J7): Exposes raw Pair 1 (RJ45_VCC_1, RJ45_GND_1) and Pair 3 (RJ45_VCC_2, RJ45_GND_2) conductors on a 2.54mm pitch header for secondary power injection or tapping.
Satellite Local Power Header (J9) & Long-Distance Regulation: A 2-pin 2.54mm header (SAT_3V3, GND). On long cable runs where cable IR drop is non-negligible, users can slice JP18 (and optionally JP17), send higher voltage (12V/24V) down Pair 3 (cut JP2 and JP3 on the hub first), and connect an off-the-shelf compact buck regulator between J7 and J9.
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.
Power Status LED (LED1) & Cuttable Jumper (JP19): A green 0805 power indicator illuminates whenever SAT_3V3 is energized. Solder jumper JP19 allows severing the LED ground connection with a hobby knife to remove the LED's current draw in battery-powered applications.
Cable Shield Isolation (JP13): Cuttable solder jumper on the bottom side connects the RJ45 metal shield to RJ45_GND_1 by default, allowing single-point grounding configurations when required.

What is the Satellite?​

Physical Specifications​

Capabilities & Architecture​

1. Differential I2C Bus Endpoint (PCA9615)​

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

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

4. Power & Auxiliary Flexibility​

Further Reading​