LD2410 Pinout, Baud Rate and Power Supply

The original LD2410 and the Bluetooth LD2410B share a slim 7x35mm board with five pads at 1.27mm pitch. Hi-Link numbers them OUT, UART TX, UART RX, GND, VCC from pin 1. The LD2410C is a squarer 16x22mm board with holes at the standard 2.54mm pitch, and its order starts with the serial pins: TX, RX, OUT, GND, VCC.

• Original and B: OUT, TX, RX, GND, VCC. Fine pitch, so use the adapter cable or a 1.27mm header.
• B-P: the same B board with pins already fitted.
• C: TX, RX, OUT, GND, VCC. Takes a normal header and breadboard jumpers.
• S: 3V3, GND, OT1 (serial TX), RX, OT2 (presence output). Different voltage, different baud.

GND and VCC sit side by side at pins 4 and 5 on all three 5V boards. That is the one constant worth memorising. For everything else, trust the print on the board you hold over any diagram drawn for a different version.

Pick a hardware UART whenever you can. On a classic ESP32 that is UART2 on GPIO16 and GPIO17; on an ESP32-C3 any free GPIO pair routed to a hardware UART works. A CH340 or CP2102 USB adapter handles 256000 on a PC, which is how Hi-Link's configuration tool connects.

• Data frames start with the bytes F4 F3 F2 F1 and end with F8 F7 F6 F5.
• Command frames start with FD FC FB FA and end with 04 03 02 01.
• Normal mode reports target state, moving and still distance, and energy.
• Engineering mode adds the energy value of every gate.

You can lower the baud rate with a configuration command, from the phone app on Bluetooth boards, or with the ESPHome baud_rate select. Options run from 9600 up to 460800. Drop to 115200 if your board only offers a software serial port, then change your code to match.

The LD2410S breaks the pattern: it defaults to 115200 and uses its own protocol, covered on the version comparison. For the full frame layout, the datasheet walkthrough goes byte by byte.

On a dev board, take power from the 5V or VIN pin, which comes straight from USB. The 3.3V regulator pin is the wrong source for the 5V boards. Some Hi-Link documents for the B and C list 5–12V on VCC, yet every version recommends 5V, so treat 5V as the target and anything higher as untested territory.

• USB phone chargers rated 1A or more are plenty for a sensor plus an ESP32.
• Keep the power leads short; long thin jumpers add drop and noise.
• A 10–100µF capacitor across VCC and GND near the module steadies a sagging rail.
• Share ground between the sensor and the microcontroller, always.

The logic side runs at 3.3V even though the supply is 5V. The TX and OUT pins swing to 3.3V, which an ESP32 or ESP8266 reads directly. The RX pin expects 3.3V too, so a 5V Arduino Uno should talk to it through a divider or a level shifter. Wiring for each board lives in the ESP32 and Arduino guide.

That number decides the build. A 2,000mAh USB power bank feeds a C and an ESP32 for well under a day, so the 5V boards belong on mains or USB power. If the sensor must run from cells, pick the LD2410S, which Hi-Link rates at about 0.1mA average when it reports once a second.

1. Add your microcontroller's draw: an ESP32 on Wi-Fi averages far more than the sensor.
2. Decide whether the controller can sleep; the S can wake it through its presence pin.
3. Size the supply for peaks, not averages.

Turning Bluetooth off on a B or C, through the app or the ESPHome bluetooth switch, closes the radio to anyone nearby with the app. It does not turn a 5V board into a battery part. For long-life nodes, the LD2410S notes cover the trade-offs.

That makes a standalone occupancy switch possible: sensor, 5V supply and a small transistor or logic-level relay module, no code at all. The pin cannot drive a relay coil directly, so put a transistor, MOSFET or a relay board with an opto-isolated input in between.

• Set the timeout (default 5 seconds in ESPHome) long enough that reading or typing does not drop the light.
• Flip out_pin_level if your relay board triggers on low.
• On boards with a light sensor, the light function can gate OUT so it only fires in the dark.

Parameters you set over serial or Bluetooth are stored on the module, so the OUT behaviour survives a power cut. Configure once with the HLKRadarTool app or a USB adapter, then install the sensor with just three wires: VCC, GND and OUT.

Wiring OUT to a GPIO alongside the UART is also handy in ESPHome. It gives Home Assistant a presence signal that keeps working even while the serial side is busy in engineering mode.