LD2420 24GHz Human Presence Sensor

The LD2420 24GHz radar presence sensor is designed for indoor projects that need to know whether a person is in a monitored area, including when they are making only small movements. It uses FMCW radar rather than changes in body heat, allowing it to detect normal movement, subtle movement and the small motions made by someone sitting or standing relatively still. The module provides a straightforward digital presence output alongside a UART interface for reading presence, approximate target distance and radar energy data. Its detection area can be adjusted using configurable distance gates, with separate trigger and hold thresholds to help balance reliable detection against unwanted activations. The LD2420 uses its own communication protocol and is supported by the ESPHome LD2420 component. Community-developed Arduino libraries are also available (although some limit the sensor's features), however the LD2420 is not compatible with software libraries written specifically for the LD2410 family. Unlike a conventional PIR sensor, radar does not need a warm body to move across distinct detection zones. This makes the LD2420 useful for occupancy sensing in offices, living spaces and work areas where someone may remain seated for an extended period. Radar can pass through some non-metallic materials and may detect movement outside the intended area. Careful positioning and adjustment of the distance gates and thresholds can help reduce detections through thin walls, doors or enclosures. The module operates directly from 3.3V and is well suited to ESP32 and other 3.3V microcontroller projects. It comes with a pre-soldered 2.54mm header and is suitable for use with breadboards and jumper wires. Which presence sensor should I choose? The LD2410C, LD2410B and LD2420 are all 24GHz radar presence sensors capable of detecting normal movement and the smaller movements made by a relatively stationary person. The main differences are their physical format, supply requirements, configuration options and software compatibility.

* The LD2410C is a convenient general-purpose option, with a compact breadboard-friendly layout, Bluetooth configuration and broad support from existing LD2410 Arduino and ESPHome integrations.

* The LD2410B provides similar LD2410 sensing and software compatibility in a longer, narrower format, with both pre-soldered and headerless variants available.

* The LD2420 (this product) is a separate 3.3V design with its own serial protocol and threshold-based calibration system, making it better suited to projects that specifically require native 3.3V power or its different detection characteristics.

Note: Sensors of this type are often described commercially as “mmWave” sensors. Strictly speaking, 24GHz has a wavelength of approximately 12.5mm, just outside the conventionally defined millimetre-wave range of 10mm to 1mm. Presence sensor comparison

LD2410C LD2410B-P LD2420

Supply voltage 5V 5V 3.3V

Signal levels 3.3V compatible 3.3V compatible 3.3V

Configuration Bluetooth or UART Bluetooth or UART UART

Reported target information Separate moving and stationary target data Separate moving and stationary target data Presence, distance and radar energy data

Detection tuning Separate moving and stationary sensitivity for each distance gate Separate moving and stationary sensitivity for each distance gate Per-gate trigger and hold thresholds with calibration support

Typical maximum range Approximately 6m Approximately 6m Up to approximately 8m

Arduino compatibility Established LD2410 libraries Established LD2410 libraries Uses a separate LD2420 protocol and software integration

ESPHome compatibility ESPHome LD2410 component ESPHome LD2410 component Separate ESPHome LD2420 component

Physical format Compact, breadboard-friendly PCB Long, narrow PCB Compact square PCB

Header options Pre-soldered header Pre-soldered or headerless variant Pre-soldered header

Best suited to General prototyping, Bluetooth tuning and established software support Projects needing a narrow PCB or direct integration without headers Native-3.3V projects and threshold-based calibration

Features

* 24GHz FMCW radar presence sensing

* Detects movement, micro-movement and relatively stationary people

* Detection range of up to approximately 8m for moving targets

* Close-range detection from approximately 0.2m

* Approximate target distance and radar energy reporting

* Configurable minimum and maximum detection distance

* Per-gate trigger and hold thresholds

* Calibration support for measuring background energy

* Adjustable presence timeout

* Simple digital occupied/unoccupied output

* UART data and configuration interface

* Dedicated ESPHome LD2420 integration

* Native 3.3V operation

* Pre-soldered breadboard-compatible 2.54mm header

Specifications

Sensor type 24GHz FMCW radar presence sensor

Detection Movement, micro-movement and relatively stationary people

Detection range Approximately 0.2m to 8m, depending on target and installation

Maximum moving-target distance Up to approximately 8m

Maximum micro-movement distance Up to approximately 6m

Detection angle Approximately ±60°

Supply voltage 3.0V to 3.6V DC

Typical supply voltage 3.3V DC

Average operating current Approximately 50mA

Interfaces UART and digital presence output

UART baud rate 115200 baud on the supplied v1.6.1 firmware

Logic level 3.3V

Bluetooth Not supported

Pin spacing 2.54mm

Dimensions Approximately 20 × 20mm

Protocol compatibility LD2420-specific UART protocol

Firmware v1.6.1+

Resources

* LD2420 Sensor in ESPHome

* LD2420 datasheet

Pinout We tested our initial batch of these sensors and they were running firmware version 1.6.1 or greater (this matters for the pinout):

1 3V3 3.3V power input. Do not connect this module to a 5V supply.

2 GND Ground connection.

3 OT1 TX

4 RX RX

5 OT2 Secondary digital output. Function may vary with firmware and configuration.

Package Contents

* 1x LD2420 24GHz Human Presence Sensor (header pre-soldered)