Occupancy-aware room lighting
Wire OUT to a microcontroller or relay so lights stay on while someone is present, including when they sit still at a desk or couch, and turn off only after the configured absence delay.
LD2410C mmWave Radar
A 24GHz FMCW mmWave radar module from Hi-Link that detects both moving and stationary humans indoors, with a simple presence pin and a configurable UART interface.
What is the LD2410C mmWave Radar?
The LD2410C is a 24GHz millimeter-wave radar presence sensor built around Hi-Link's FMCW (frequency-modulated continuous wave) engine. Instead of sensing body heat the way a PIR does, it measures radar reflections, so it can detect a person who is sitting, lying, or otherwise nearly motionless, not just someone walking through the beam. It covers roughly 0.75 to 6 meters (eight 0.75 m distance gates) across a wide detection angle of about plus or minus 60 degrees, operating in the 24 to 24.25 GHz ISM band with a 250 MHz sweep bandwidth.
The module gives you two ways to read it. The OUT pin is a plain digital presence signal that goes 3.3V HIGH when a human is detected and LOW when the space is empty, which is all you need for basic occupancy triggers. The TX and RX pins expose a 256000-baud UART that streams richer data: moving and stationary target state, target distance, and per-gate energy. Detection behavior is fully configurable over that serial link or wirelessly through Hi-Link's HLKRadarTool app via the module's built-in Bluetooth, letting you set the maximum detection gate, per-gate sensitivity, and the absence (no-one) hold time.
Because it uses radar rather than heat or light, the LD2410C is unaffected by ambient temperature, brightness, or air currents, and it can work hidden behind a non-metallic enclosure. It runs from a 5V supply at roughly 79 mA average, making it a popular, low-cost upgrade over PIR sensors for reliable indoor human presence detection.
LD2410C mmWave Radar pinout
| Pin | Function | Type |
|---|---|---|
TX TX | UART TX (256000 baud) | Digital output |
RX RX | UART RX (256000 baud) | Digital input |
OUT OUT | Digital presence: HIGH = human detected, 3.3V | Digital output |
GND GND | Power | Power in |
VCC VCC (5-12V) | Power | Power in |
Specifications
- Operating voltage
- 5 V (max 12 V)
- Interface
- UART
- Dimensions
- 22.2 × 4.5 × 16 mm
Verified from the Tinkered component library · Shenzhen Hi-Link Electronic (HLK-LD2410C).
Circuit requirements
- Power VCC from 5V DC nominal (the module accepts up to 12V). Use a supply rated for at least 200mA; average draw is about 79 mA but the radar produces current spikes well above that.
- All signal pins (OUT, TX, RX) are 3.3V logic and are not 5V tolerant. The OUT pin drives 3.3V HIGH on detection, which a 5V board still reads as a valid HIGH, so OUT can connect directly to an Arduino digital input.
- When driving the sensor's RX from a 5V microcontroller TX (for example an Arduino Uno), drop the line to 3.3V with a level shifter or resistor divider. The sensor TX to microcontroller RX line can connect directly.
- The UART runs at 256000 baud, 8 data bits, 1 stop bit, no parity. Use a hardware serial port; SoftwareSerial on an Uno is not reliable at this rate, so an ESP32 or a board with a spare hardware UART is a better host.
- OUT is a push-pull digital output, so no external pull-up or pull-down resistor is required.
- Radar needs a clear, non-metallic line of sight. Mount per the datasheet (ceiling at 2.6 to 3 m or wall at 1.5 to 2 m), keep it away from fans, curtains, and HVAC airflow, and allow the module a moment to stabilize after power-up before trusting the first reading.
Board compatibility
The LD2410C mmWave Radar connects to any of the microcontrollers supported in Tinkered. Mind the 5 V logic level on 3.3 V boards.
Common LD2410C mmWave Radar mistakes
Feeding 5V into the TX or RX pins
The serial pins are 3.3V logic and not 5V tolerant. Wiring a 5V board's TX straight into the sensor RX can damage it. Add a level shifter or divider on that line, even though OUT and the sensor's TX can be read directly by a 5V input.
Using SoftwareSerial at 256000 baud
The default baud rate is 256000, which is too fast for SoftwareSerial on an Uno or Nano and produces garbled frames. Configure the UART on a hardware serial port, or use a host like the ESP32 with multiple hardware UARTs.
Treating it like a PIR motion sensor
The LD2410C also senses stationary and micro-moving people, so a seated occupant keeps OUT HIGH. Without tuning per-gate sensitivity and the no-one hold time, it can appear to never switch off, or it can trip on small movements you did not intend to catch.
Mounting behind metal or facing moving objects
Metal blocks the 24GHz signal, and fans, swaying curtains, HVAC airflow, or pets all reflect radar and cause false detections. Follow the datasheet mounting geometry and keep the field of view clear of moving clutter.
Powering it from a weak 3.3V rail
VCC is a 5V input, not 3.3V, and the supply must handle over 200mA including current spikes. Undersized rails or thin USB leads cause brownouts that show up as random false triggers or dropouts.
LD2410C mmWave Radar datasheet
Official LD2410C mmWave Radar datasheetShenzhen Hi-Link Electronic (HLK-LD2410C)
Popular LD2410C mmWave Radar projects
Home Assistant presence sensor
Pair the UART with an ESP32 running ESPHome to publish moving and stationary target state, distance, and energy per gate into Home Assistant for room-level presence automations.
Smart HVAC and standby control
Use radar presence to keep heating, cooling, or a monitor active only while a room is genuinely occupied, cutting energy use compared to timer-only or PIR-based control.
Bedside still-presence monitor
Take advantage of stationary detection to sense a person lying in bed, using the UART distance and energy data as a low-cost, contactless presence indicator.
More sensors
Build with the LD2410C mmWave Radar.
Drop the LD2410C mmWave Radar into a circuit, write firmware, and simulate it in your browser, then deploy to real hardware. All in one editable Tinkered project.