Svet Črnil

Description

Detection of presence even in small movements

In automatic lighting, it is often not enough to know that someone just walked through the door. The system must also take into account a person sitting at a table or moving slightly. Hi-Link HLK-LD2401 is a radar module for detecting human presence in internal spaces. Works in the waist 24 GHz and is intended for installation in its own electronic projects, smart lighting, space management and prototypes with Arduin; or ESP32.

The sensor detects movement and micro motion. You can use the result as an input to your application: to display occupancy, trigger timer, change lighting or record event. The final behaviour of the system is determined by the controller program. The module itself therefore does not replace the design of the device, the correct installation and the test in the space where it will actually be used.

Basic properties of module HLK-LD2401

• Manufacturer and model: Hi-Link HLK-LD2401.
• Radar technology: FMCW in the frequency range 24 to 24,25 GHz.
• Detection of presence up to 6 m under appropriate conditions.
• Selection of distance steps 0,75 m or 0,2 m; a smaller step means a shorter covered area, up to 1,6 m at eight steps.
• The radar visual range according to the manufacturer is approximately ±60 degrees.
• GPIO and UART outputs; digital signal level 3,3 V.
• Base module power supply: 3,3 V, the source should provide more than 200 mA; that average current is approximately 74 mA.
• Setting range, sensitivity and delay in absence through supported module settings.
• Dimensions of the basic module about 18 x 22 mm; check the execution of the connections of the delivered piece.

The maximum range is not a guaranteed distance for each objective and each space. The result is influenced by installation, orientation, reflections, moving objects and settings. When selecting the area, it is important that the sensor monitors that part of the space you are interested in. Excessive reach can cause reactions due to events outside the desired area.

Children, adults and domestic animals: what the result means

LD2401 is a presence sensor, not a camera or a human classification system. From his signal, we cannot conclude that a person is a child or an adult. Animals may also affect radar detection, so such a project requires a real test with the desired objective and at the intended location of installation. The manufacturer does not confirm a reliable distinction between children, adults and domestic animals.

For example, for a project in a children’s room, you can test whether the sensor detects presence in a specific area and how long the output remains active when sitting still. To monitor the area where the animal is, check the response at different positions and distances. The result of such a test is the basis for automation settings, not proof that any situation will be detected.

Do not use the module as the only means to control child safety, as a medical monitor or as a safety guard for the machine. Its reasonable use is automation of comfort, development and undemanding perception of occupancy. Where a missed event could cause danger, a solution that is properly planned and verified for that purpose is necessary.

GPIO or UART: select the information the project needs

Digital output is practical when you need simple information about the detected presence. The controller reads it and turns on the function or starts the countdown according to its logic. In the UART serial connection, the application can use data transmitted by the selected module version. Format and commands always check in protocol HLK-LD2401.

When connecting to the ESP32, check the concrete plate, its free connections and the permitted load on the power supply. Do not connect sensor output directly to the relay coil or network user. You need an appropriate interface to control the load. UART TTL is also not directly identical to RS232 or RS485.

Set in space by step

1. First, determine the area where you want to detect presence and the intended height of installation.
2. Connect the module after the verified attachment layout and start with a simple result view.
3. Check the status of the empty space and any responses when the fan or other moving objects operate.
4. Try entry, exit, sitting and small movements in different locations of the area.
5. Adjust sensitivity and distance, then set a reasonable shutdown delay.
6. After installation in the final housing, repeat the test and record the final settings.

For the housing, follow the manufacturer’s instructions for the radar window and antenna position. Metal parts can change or disable operation before the antenna. The distance between the sensor and the elements of the housing is also important. The test on the open table therefore does not confirm the same performance after final assembly.

Example of automation with ESP32

A development example is a table lamp where the ESP32 reads the presence signal and starts the timer only when the sensor reports absence. Discontinue timer presence detected. The user can add a manual key and status view. Thus, behavior is understandable and can be observed during testing.

To fix the problems in the initial version of the program, record the time of the change of exit and the reason for the command to the lamp. If the lamp is switched off prematurely, you can distinguish the problem of perception from the error in the timer. When operating through the network, the local logic should remain clear even when the connection is lost. These decisions are part of your project, not the automatic function of the sensor module.

For a student project, it is useful to compare with another way of perception: you observe both sensors in the same space, maintain the same positions and record the differences. In doing so, do not only assess the maximum reach. Also important are delay, false responses, perception of a dormant person, and simplicity of connection to the remaining electronics.

Documentation and local support

Official page Hi-Link HLK-LD2401 contain technical data, communication protocol and software tools. Additional available presentation HLK-LD2401 with manufacturer's development files. Select LD2401 when downloading, as similarly named modules use different settings and protocols.

At the Board of Blacks in Ljubljana, we can jointly check the power supply, connection and method of integration into your system. Send the code to the development tiles, sketch the space and destination. This makes it easier to select suitable settings and components and determine a test that will show whether the module fits your project.