Verified 2026-10

SparkFun Qwiic Soil Moisture Sensor (Capacitive)

Soil-moisture probe on a 3.3 V Qwiic breakout: a capacitive plate inside the PCB is read by an Infineon CY8CMBR3102 CapSense Express controller and reported over I2C at 0x37 by default, so nothing metal touches the soil and nothing needs wiring beyond a Qwiic cable.

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Logic level3.3 V

Specs

MCU	Infineon (Cypress) CY8CMBR3102 CapSense Express capacitive sensing controller, I2C slave

Pinout

8 pads, as the vendor numbers them.

#	Name	Function	Signals
1	GND	Qwiic connector J1 pad 1 - ground, common to the whole Qwiic chain	GND
2	3.3V	Qwiic connector J1 pad 2 - 3.3 V in. Also the anode rail for both LEDs and the high side of the I2C pull-ups	3.3V
3	SDA	Qwiic connector J1 pad 3 - I2C data, pulled up by R3 (2.2k) and shared with J2, test point TP6 and U1 pad 8	I2C SDA
4	SCL	Qwiic connector J1 pad 4 - I2C clock, pulled up by R2 (2.2k) and shared with J2, test point TP7 and U1 pad 1	I2C SCL
5	GND	Qwiic connector J2 pad 1 (second connector; numbered 5-8 here so the two 1-4 connectors do not collide) - same ground net as J1	GND
6	3.3V	Qwiic connector J2 pad 2 - same 3.3 V net as J1	3.3V
7	SDA	Qwiic connector J2 pad 3 - same SDA net as J1	I2C SDA
8	SCL	Qwiic connector J2 pad 4 - same SCL net as J1	I2C SCL

Buses

Bus	Signals	Pins	Voltage	Note
I2C ×2	SDA, SCL	SDA, SCL	3.3 V	The same two nets reach both Qwiic connectors and the four back-side test points. 2.2k pull-ups to 3.3 V sit on the back of the board (R3 on SDA, R2 on SCL) and are bridged to the rail through JP2, a 3-pole solder jumper whose 1-2-3 bridges are cut to remove them. There is no other bus on the board.

I²C / bus addresses

Address	Bus	Device	Note
0x37	I2C	CY8CMBR3102 CapSense Express controller	SparkFun gives 0x37 as the default and calls the address software-configurable: the controller's registers set it, not a board strap, so there is nothing to cut or bridge and two of these on one bus must be reconfigured in software before they will coexist.

Power

Input	3.3 V through either Qwiic connector - no regulator, no USB, no battery connector
Input range	3.3 V only. Qwiic is a 3.3 V bus, and the CY8CMBR3102 has no 5 V tolerance, so a 5 V host needs a level shifter on SDA/SCL as well as a 5-to-3.3 V supply

SparkFun publishes no current draw for this board, so none is recorded. Two LEDs: a red power LED fed from 3.3 V through R1 (4.7k) with JP1 as a 2-pole solder jumper bridged by default, and a blue STAT LED whose anode goes to 3.3 V through R7 (2.2k) and whose cathode returns to the controller's GPO0/CS1 pin (U1 pad 6) - so the status LED is active LOW and the controller sinks it.

Notes

Two Qwiic connectors (J1 and J2, both JST-SH 1.0 mm 4-pin, right-angle) are the only places to land a cable - the board has no 0.1in header. The connectors are numbered 1-4 by the vendor; this entry numbers J2 5-8 so the two sets stay distinct in one pin list. Each connector also has two mechanical shield pads the schematic marks NC (unconnected-(J1/J2-NC-PadNC1/NC2)) - they are solder tabs, not signals. Four 1.0 mm test points on the back carry GND (TP4), 3.3V (TP5), SDA (TP6) and SCL (TP7); the vendor prints and numbers them as TP4-TP7 but they are not a connector, so they are described here rather than numbered into `pins`. The sensing plate is copper in the PCB itself, driven from U1 pad 7 (CS0) through R6 (560R) to the plate net; the board is meant to be pushed into soil up to the printed ruler, and only the plated edge goes in the dirt, the two Qwiic connectors and all components are at the top end and must stay dry. U1's own connections, for anyone probing: pad 1 SCL, 2 CMOD (modulation cap C3 2200 pF to GND), 3 VCC (a bypass node with C4 0.1 uF to GND, not a supply input), 4 VDD (from 3.3 V, C1 0.1 uF and C2 1.0 uF), 5 GND, 6 GPO0/CS1 (blue STAT LED cathode), 7 CS0, 8 SDA. JP2's 3-pole jumper is bridged 1-2-3 on delivery, so both pull-ups are live; cutting the bridges is the only way to take them off the bus. SparkFun's own docs for this board are an introduction page and a calibration note and carry no pin table - the pin map above comes from the KiCad files' nets, and the labels from the same file, because the vendor publishes no numbered pinout.

Provenance

Every figure on this page was read from the 5 sources below and last checked on Oct 21, 2026.