What baud rate does the DFRobot SEN0605 use by default?

9600 bps, 8N1. It is a Modbus-RTU slave; default address 1.

What supply voltage does the DFRobot SEN0605 need?

DC 5–30 V (Low (RS-485 bus-powered class)).

How do I change the DFRobot SEN0605 Modbus address?

Write the device-address register with function code 0x06, one device on the bus at a time, then power-cycle. See the Configuration section above.

Is the DFRobot SEN0605 compatible with the Sankhya platform?

Yes — it is in the Sankhya RS-485 sensor library and the firmware-generation pipeline can produce node firmware for it.

What does the DFRobot SEN0605 not measure?

The DFRobot SEN0605 reports N-P-K only — it does not report moisture, temperature, EC, pH, salinity and TDS. On the same RS-485 bus, add moisture: DFRobot SEN0600; temperature: DFRobot SEN0600; EC: DFRobot SEN0603.

How many Modbus registers does the DFRobot SEN0605 expose?

This guide documents 14 registers, read with function code 0x03 and written with 0x06 where the register is RW. Documented entries include Nitrogen temporary value, Phosphorus temporary value, Potassium temporary value, Nitrogen coefficient high word, Nitrogen coefficient low word and Nitrogen deviation.

Why are the first N-P-K registers called temporary values?

The device documentation distinguishes them from the coefficient and deviation model. Preserve that distinction when exporting or comparing readings.

Does the SEN0605 also measure moisture?

No. Pair it with a moisture-temperature probe if water context is needed.

Home / Sensors / DFRobot SEN0605

DFRobot · RS-485 sensor

DFRobot

DFRobot SEN0605

DFRobot N-P-K probe. NPK uses an IEEE-754 coefficient model (two-register decode).

✓ Verified for SankhyaN-P-KVerification 0.90 · datasheet-confirmed

At a glance

The DFRobot SEN0605 is a single-parameter RS-485 soil probe reporting N-P-K over Modbus-RTU on RS-485 at 9600 bps, 8N1, on DC 5–30 V. This guide documents 14 registers, default Modbus address 1. It does not report moisture, temperature, EC and others. For those on the same bus: moisture → DFRobot SEN0600; temperature → DFRobot SEN0600. Sankhya firmware profile: DFROBOT_NPK_coeff.

Sankhya Farms integration

N-P-K decoding that does not flatten the coefficient model

The DFRobot SEN0605 exposes more than three simple nutrient words. Sankhya Farms uses the DFROBOT_NPK_coeff profile to distinguish temporary N, P and K values from the high-word/low-word coefficient pairs and signed deviations used by the device's internal model. The open-source node can collect the resulting fields at 9600 baud and send meaningful nutrient values to the free cloud dashboard rather than treating every 16-bit register as an independent reading.

This model is most useful where the N-P-K response can be checked: a field or pot trial, greenhouse experiment, home-garden comparison, educational bench or calibration exercise. Moisture, temperature, EC and pH are not reported, so a serious interpretation may require neighbouring sensors or reference tests. The dashboard provides history and context; it does not make an indirect nutrient estimate equivalent to laboratory analysis. The buried probe may be considered for a compatible substrate, but a hydroponic reservoir requires a liquid-rated nutrient or water-quality instrument. Large changes should be investigated before they become fertiliser decisions.

Why a generic decoder falls short: each coefficient spans two Modbus words and represents an IEEE-754 value. Word order and signed deviations matter. Use the verified map rather than guessing from the SEN0605 name.

Value lookup

Where are the SEN0605 N-P-K values and coefficients?

The temporary nitrogen, phosphorus and potassium words are 001EH, 001FH and 0020H. Nitrogen coefficient words begin at 03E8H, phosphorus at 03F2H and potassium at 03FCH; their paired high and low words must be combined as documented, with separate signed deviation registers. Sankhya's named profile performs that structured lookup instead of presenting half of a floating-point coefficient as a sensor value.

Why are the first N-P-K registers called temporary values?: The device documentation distinguishes them from the coefficient and deviation model. Preserve that distinction when exporting or comparing readings.
Does the SEN0605 also measure moisture?: No. Pair it with a moisture-temperature probe if water context is needed.

Quick reference

Bus & electrical specs

Note. SEN0605 NPK is not a simple integer read — each element is a coefficient/deviation pair decoded as an IEEE-754 float. Requires dedicated firmware handling.

Protocol

Modbus-RTU over RS-485

Default baud

9600 bps

Serial format

8N1

Function codes

0x03, 0x06

Supply voltage

DC 5–30 V

Power

Low (RS-485 bus-powered class)

Default address

Ingress / housing

IP68

Probe / element

316 stainless steel

Operating temp.

−40 to +80 °C (probe)

Firmware profile

DFROBOT_NPK_coeff

Specs sourced from: Official DFRobot wiki (SEN0600–SEN0605 product pages).

Modbus-RTU register map

Function codes 0x03, 0x06 at 9600 bps, 8N1. Data registers are read with 0x03; configuration registers are written with 0x06. PLC column shows the 4xxxx Modbus holding-register convention.

Register	PLC	Parameter	Type	Scale	Unit	R/W	Notes
001EH	40031	Nitrogen temporary value	uint16	1	mg/kg	RW
001FH	40032	Phosphorus temporary value	uint16	1	mg/kg	RW
0020H	40033	Potassium temporary value	uint16	1	mg/kg	RW
03E8H	41001	Nitrogen coefficient high word	uint16	—	—	RW	IEEE 754 float high 16 bits.
03E9H	41002	Nitrogen coefficient low word	uint16	—	—	RW	IEEE 754 float low 16 bits.
03EAH	41003	Nitrogen deviation	int16	1	—	RW
03F2H	41011	Phosphorus coefficient high word	uint16	—	—	RW
03F3H	41012	Phosphorus coefficient low word	uint16	—	—	RW
03F4H	41013	Phosphorus deviation	int16	1	—	RW
03FCH	41021	Potassium coefficient high word	uint16	—	—	RW
03FDH	41022	Potassium coefficient low word	uint16	—	—	RW
03FEH	41023	Potassium deviation	int16	1	—	RW
07D0H	42001	Device address	uint16	1	—	RW
07D1H	42002	Baud rate	uint16	1	—	RW

Example poll

Worked query

Configuration

Changing address & baud rate

This probe is configured over the same RS-485 bus using Modbus write commands (function code 0x06). Configure one device at a time on the bus.

Set the Modbus slave address by writing register 07D0H (PLC 42001) with function code 0x06.
Set the baud rate by writing register 07D1H (PLC 42002).
Power-cycle the probe after a configuration write for the change to take effect.

Field notes

Notes & caveats

Exposes coefficient and deviation registers for internal NPK model. Not simple raw readout.

FAQ

Common questions

What baud rate does the DFRobot SEN0605 use by default?: 9600 bps, 8N1. It is a Modbus-RTU slave; default address 1.
What supply voltage does the DFRobot SEN0605 need?: DC 5–30 V (Low (RS-485 bus-powered class)).
How do I change the DFRobot SEN0605 Modbus address?: Write the device-address register with function code 0x06, one device on the bus at a time, then power-cycle. See the Configuration section above.
Is the DFRobot SEN0605 compatible with the Sankhya platform?: Yes — it is in the Sankhya RS-485 sensor library and the firmware-generation pipeline can produce node firmware for it.
What does the DFRobot SEN0605 not measure?: The DFRobot SEN0605 reports N-P-K only — it does not report moisture, temperature, EC, pH, salinity and TDS. On the same RS-485 bus, add moisture: DFRobot SEN0600; temperature: DFRobot SEN0600; EC: DFRobot SEN0603.
How many Modbus registers does the DFRobot SEN0605 expose?: This guide documents 14 registers, read with function code 0x03 and written with 0x06 where the register is RW. Documented entries include Nitrogen temporary value, Phosphorus temporary value, Potassium temporary value, Nitrogen coefficient high word, Nitrogen coefficient low word and Nitrogen deviation.

Alternatives

How this differs from similar models

How the DFRobot SEN0605 compares with the other RS-485 models in the Sankhya library. "Drop-in" means the same parameter set and the same register map, read by the same firmware profile.

Model	Relationship	Measures	Baud	Difference
DFRobot SEN0600	Sibling	Moisture, Temperature	9600	Adds moisture and temperature, drops N-P-K.
DFRobot SEN0601	Sibling	Moisture, Temperature, EC, Salinity, TDS	9600	Adds moisture, temperature, EC, salinity and TDS, drops N-P-K.
DFRobot SEN0602	Sibling	Moisture, Temperature, pH	9600	Adds moisture, temperature and pH, drops N-P-K.
DFRobot SEN0603	Sibling	EC, pH, Salinity, TDS	9600	Adds EC, pH, salinity and TDS, drops N-P-K.

Same family

Related DFRobot sensors

Run this sensor on a Sankhya node

Every sensor on this page is in our RS-485 library. Pick your model, and the firmware-generation pipeline builds the Modbus (or ASCII) polling code for an ESP32-S3 node — no hand-coding the register math.