PSF-B04 Application Guide

1.Product Introduction            

PSF-B04 is a 4-channel ultra-low-power Wi-Fi switch module based on ESP8285. It’s specially designed for mobile devices and Internet of Things applications with the most competitive package size and ultra-low energy consumption technology in the industry. Connecting users’ devices to the Wi-Fi wireless network for remote or local area network communication to achieve networking. This module can be used as a switch control for 4 household appliances. Either it can be controlled by the device button, or remotely controlled by connecting to APP (eWeLink).

PSF-B04 has various packaging methods, and the antenna supports ceramic antennas. It can be widely used in smart grid, smart transportation, smart home, handheld devices, industrial control and other fields.

Product Features:

  • Built-in 32bit MCU, and can double as an application processor
  • Support wireless 802.11 b/g/n standard
  • Wi-Fi @2.4 GHz, support WPA/WPA2 security mode
  • +20.5dBm maximum outputpower in 802.11b mode
  • Support devicebutton control
  • Support timer schedule
  • Support Wi-Fi remote control
  • Support compatible pairing mode /quickpairing mode
  • Support OTA upgrade

2.Electrical Characteristics             

2.1 Rated parameters    

Conditions: VDD=3.3V±10% , GND=0V; test at room temperature 25°C.

2.2 Wi-Fi parameters  

Conditions: VDD=3.3V±10% , GND=0V ; test at room temperature 25°C.

3.Module Type and Pin Definition 

3.1 Module type        

PSF-B04 top view

3.2 Sequence of pin arrangement 

PSF-B04 module provides 4-channel switch control interface, Wi-Fi status light interface, UART serial port.

Top view of module pins:











Bottom view of module pins:


3.3. Pin definition     

Pin definition and function description

4.Function Description        

4.1. Module function  

PSF-B04 module can be used as a 4-channel switch, which can control the switch locally or remotely through APP.

The following is the function description:

  1. Pairingmethod: quick pairing mode / compatible pairing mode.

Press and hold the button (IO0 pull-down, default high level) for more than 5s to enter the quick pairing mode. When it is in the quick pairing mode, press the button for more than 5s again to enter the compatible pairing mode. APP can be configured in both modes. Please refer to 4.3 for details of the configuration method.

  1. Switch:
  2. In the normal state: click the button (pull down any IO port of 4 channels for more than 100ms) to control the relay on and off (four relay switches corresponding IO port output high/low level)
  3. In the pairing mode: click the button to exit the pairing mode.
  4. Timer: including single, count down, repeat, and loop timer, see details in 4.5.
  5. Power-on status configuration: The power-on switch status can be configured on or off through the APP, and the default power-on status is off.

4.2. Wi-Fi status indicator light description

The flashing mode of the Wi-Fi status light on the device represents the its current network working status. The specific status includes the following seven types:














The flashing of the Wi-Fi status light is in a cycle of 2 seconds, as shown in the figure, the low-level light is on and the high-level light is off. Detailed explanation of each status:

  1. Normal: The device is working normally and the connection to the cloud server is normal.The device can be only controlled through the APP in this mode.
  2. NO Wi-Fi: The device cannot connect to the router.
  3. No Server: The device has been connected to the router, but it cannot connect to the server (also known as”cannot access the Internet”).
  4. Unregistered: The device has not been bound to account. The device needs to be bound to the eWeLink account to connect to the cloud server. You can bind the device by tap “Add Device” in the eWeLink APP.
  5. Upgrade: Indicates that the device is upgrading the firmware.
  6. Setting G1: Indicates that the device is in compatible pairing mode. The device obtains the necessary information provided by the APP to join the service network, including router SSID, password, server IP, port number, etc in the setting mode.
  7. Setting G2: Indicates that the device is in quick pairing mode. The device obtains the necessary information provided by the APP to join the service network, including router SSID, password, server IP, port number, etc in the setting mode.

The device obtains information in different ways in the two modes, read below section for details.

4.3 The Wi-Fi module basic workflow      

  1. Configuration
  2. Compatible pairing mode: The mobile terminal joins the device AP as a station to form a local area network to realize data interaction. When the device is in the quick pairing mode (G state, see details in 4.2 Wi-Fi status indicator light description), press and hold the pairing button for 5S, the device enters the compatible pairing mode. Click “add device” on the eWeLink APP, connect the device hot spot in the phone setting page manually with SSID: ITEA 10000XXXX and password12345678 to connect the device to the Internet.
  3. Quick pairing mode: The Wi-Fi module is in promiscuous mode, and the encrypted message containing information such as SSID and password from the mobile terminal is obtained by empty packet capture. The device enters the quick pairing mode by pressing the pairing button for 5S when it is in the A~D flashing modes. Click “add device” on the eWeLink APP, enter the SSID and password of the router to connect the device to the Internet.
  4. Online

The module goes through the following process from power-on to connecting to the server:

  1. Join the configured router and connect to the Internet.
  2. Connect to the server.
  3. Register the device and bind it to the eWeLink account.
  4. Obtain device application parameters and stay online.

When the connection/acquisition fails in the above steps, there are corresponding back-off strategies and reconnection mechanisms to ensure that the device is stable and keep online.

  1. Upgrade

The module connects to the upgrade server, downloads and updates to the latest version of the firmware to realizes the online upgrade of the device.

4.4 Timer function

The timer function is configured through the APP, and the timer is divided into the following four types:

  1. Single timer: executeat a specified time.
  2. Count downtimer: execute after the setting time.
  3. Repeattimer: repeat the operation every week.

4.5 Timer function description  

PSF-B04 supports timer. The eWeLink APP provides four timing modes to facilitate the use in more scenarios.

  1. Single timer: This is the most common timing setting, allowing users to set the work schedule of the device. For example, turn on/off the device at 8:30 am every Wednesday, etc. It is similar to the setting of an alarm clock, timing is very convenient to use especially for devices that are repeatedly running at certain moments.
  2. Count downtimer: The count down is to facilitate the user to perform one-time timing operations, such as turn on/off the device after 30 minutes. It is very convenient to turn off a device after running a period of time. This device supports up to 24 hours of count down.
  3. Repeat timer: Repeat the operation every week. For example, set an alarm clock for working time. After the time is set, select execute dates (a week optional), and the alarm clock will turn on at the set time within the selected days.


5.Wi-FiRadio Frequency Index       

Conditions: VDD=3.3V±10% , GND=0V ; test at room temperature 25°C.

5.1 Sensitivity

5.2 Adjacent frequency suppression  


  1. 2Mbps is measured in the 802.11n mode, the MCS =7, the GI = 200uS.
  2. Up to + 21.5dBm output powerin 11b mode.

6.PCB Design 

Precautions for PCB layout and module layout:

  1. Pay attention to the placement of the module during PCB layout, especially the antenna part of the module, as far as possible away from interference sources: magnetic components (such as motors,inductance, transformers, etc.), high-frequency signal devices (such as crystal oscillators, high-frequency clock signals, etc.).
  2. The upper and lower layers of the PCB where the module is placed should not be routed as much as possible. Do the copper-clad processing, and the PCB from the module antenna to the nearest pin of the module should be hollowed out as much as possible.
  3. The module PCB antenna area and the 15 mm extension area need to be clear (copper, trace on the board, and component placement are strictly prohibited), refer to the following figure:
  4. Place the module’s power supply (VCC) pin capacitance and other module pin capacitances, resistors as close as possible to the module pins, and the tracepath should be short.

7.Packaging Information    

Package size diagram:


  1. Grzegorz Larma

    PSF-B04 connected with the relay module does not turn on, only disconnecting the output to the 4th channel allows to start. How to solve this problem?

    • winnie.wu

      When the module starts, PIN8 should keep low level until the module starts

  2. Przemo

    Pin #7 STATUS – which ESP GPIO is?

  3. Wayne

    I have a unit that is stuck in interlock mode (only one relay will energize at a time). Is there a way to disable on the PCB?

    • Rudy Beulens

      Push 20sec the pushbutton belowe the pcb. Thuis Will disable the interlock function. Worked with both of my boards.

  4. Bence Juhász

    Hello, I bought this today, and I can’t make it work.. First, how can I add the led to the STATUS pin? I only got 0.20V from there. How can I incrase the voltage? I don’t really understand the description for this. . Thanks for the answer!


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