1001 RPi0 4G CAT1-ETH(RS485 OPT
Keywords
Raspberry Pi Zero,Raspberry Pi Zero W,Raspberry Pi Zero WH,Raspberry Pi Zero 2 W, Cat1 4G LTE, USB2.0-A, Ethernet, Expansion Board, USB HUB, RS485, driver-free
I. Introduction
The Raspberry Pi Zero series (including Zero, Zero W(H), and Zero 2W) is a low cost-effective embedded system platform with a compact size, low power consumption, and decent performance, making it suitable for many lightweight application scenarios. The Zero series, despite its compact size, offers many expansion interfaces. The underside of the board features gold-plated test points for USB and power connections. These USB and power test points allow us to connect various types of peripherals for expansion.
This expansion board is a USB hub, connecting the expansion board to the USB port of the Zero via pogo pins. It extends four USB ports through the USB connection: one USB port is converted to a 100Mbps wired Ethernet connection, one USB port is connected to a 4G Cat1 module, and two USB2.0-A host interfaces are provided. There is also an RS485 version available, which can convert one USB port to an RS485 interface.
4G Cat1 is a cost-effective module designed for medium-speed IoT applications around 10Mbps. The 10Mbps downlink and 5Mbps uplink speeds can meet the vast majority of networking and transmission needs. This module is plug-and-play on Raspberry Pi and Ubuntu OS, automatically recognized as a 4G connection without needing drivers or dial-up configurations, making it convenient for users to develop applications. It have two versions, CAT 1 and CAT 1-EU.
(Note: When using this expansion board, the Raspberry Pi Zero development board cannot utilize the OTG function. If you need to use the OTG function, all interfaces on the expansion board will become unavailable.)
II. Hardware Spec
2.1 One USB-C power input, similar to the micro USB PWR on the Raspberry Pi Zero; choose one of the two options.
2.2 One 10/100Mbps Ethernet.
2.3 One 4G LTE Cat1 module.
2.4 One Nano SIM card and one IPEX-1 antenna.
2.5 Two USB2.0-A HS.
2.6 Four LEDs： PWR/MODE/ACT LED
2.7 One reset button for 4G module.
2.8 The RS485 version with industrial-grade power isolation, it is USB to RS485, so only one USB2.0 on board.
2.9 Aluminum alloy enclosure(OPT).
Note 1: After connecting this expansion board, the Micro USB port on the Zero will no longer be usable.
Note 2: In some systems, it is necessary to disable the OTG function and set the USB mode to Host mode.
Note 3: The board supports all versions of the Raspberry Pi Zero, including the Zero, Zero W, Zero WH, and Zero 2W.
Note 4: The board supportsother Pi with USB contacts in the same position, such as the Orange Pi Zero 2W.
Features of RS485 isolation module:
This module features an automatic flow-control high-speed RS485 isolation unit, integrating power isolation, signal isolation, RS-485 communication, and bus protection into a single RS-485 protocol transceiver module through IC integration technology. The module comes with a built-in constant voltage isolated power supply, capable of achieving 2500VDC electrical isolation withstand voltage protection. It can be connected as a slave device to an RS485 bus or function as a master device to receive and process information from various slave units.
- Supports connection of up to 64/128 nodes.
- Transmission rate up to 500Kbps.
- Extremely low electromagnetic interference (EMI).
- Operating temperature range: -40℃ to +85℃.
- Integrated power isolation, signal isolation, and bus ESD protection functions.
| model | CAT1 | CAT1-EU |
|---|---|---|
| Band | FDD：B1/B3/B5/B8 | FDD：B1/B3/B5/B7/B8/B20/28 |
| TDD：B34/B38/B39/B40/B41 | TDD：B38/B40/B41 | |
| DATA | FDD： Max 10Mbps（DL）/Max 5Mbps（UL）
TDD：Max 8Mbps（DL）/Max 2Mbps（UL） Max 6Mbps（DL）/Max 4Mbps（UL） | |
III. Work with Raspberry Pi OS
We conducted tests based on the Raspberry Pi Zero 2W.
The Raspberry Pi OS:(Raspberry Pi OS with desktop) 2024-07-04-raspios-bookworm-arm64.img.xz.
You can download the Raspberry Pi OS in:
https://www.raspberrypi.com/software/operating-systems/#raspberry-pi-os-64-bit
(If you are using the Raspberry Pi Zero (1st generation) series boards, they only support 32-bit systems. Please be sure to download the correct version.)
Different versions of Raspberry Pi OS have varying strategies for network management. Based on the 64-bit OS version, the results are as follows:
| OS version (64-bit) | Test results |
| 2023-02-21-bullseye | Driver-Free, No Dial-Up Required, Auto-identification, plug and play, automatic internet connection. |
| 2023-05-03-bullseye | |
| 2023-12-05-bookworm | Driver-Free, No Dial-Up Required, Auto-identification, but there may be instances of network connection failure,
and the OS requires the installation of DNS software. |
| 2024-07-04-bookworm | |
| 2024-11-19-bookworm | |
| 2025-05-13-bookworm | |
| 2025-10-01-trixie |
The Raspberry Pi Zero series boards only support 32-bit OS. The test results are as follows:
| OS version (32-bit) | Test results |
| 2023-02-21-bullseye | Driver-Free, No Dial-Up Required, Auto-identification, plug and play, automatic internet connection. |
| 2023-05-03-bullseye | |
| 2023-12-05-bookworm | |
| 2024-07-04-bookworm | |
| 2024-11-19-bookworm | |
| 2025-05-13-bookworm | |
| 2025-10-01-trixie |
3.1 View hardware devices
3.1.1 View USB devices
Open the terminal in Raspberry Pi OS and enter the commandlsusb, as shown in the image below:
RPi0_RS485CAT1:
RPi0_RS485CAT1EU:
RPi0_CAT1-ETH/RPi0_CAT1-EU_ETH:
Note: If the USB port on the expansion board is not connected to any device, the corresponding device number will not appear in the lsusb. For example, the Bus 001 Device 005 for RPi0_RS485CAT1 appears here because a wireless keyboard and mouse are connected. If no device is connected, this number will not be present.
3.1.2 View network devices
The 4G module is automatically recognized in the Raspberry Pi OS, requires no drivers, and is plug-and-play.
Open the terminal in Raspberry Pi OS and enter the command ifconfig -a, as shown in the image below:
We can see that eth1 is a 4G Cat1 connection (with the IP address in the image above is 192.168.5.8).
3.2 Test network devices
3.2.1 ping tests
When testing, there is a priority order: if eth0 is connected, it will be used first. If there are specific requirements for internal and external networks, please adjust the metric values of each network and the DNS server settings.
Use the -I parameter to specify which network interface to start the ping packet from, as shown below:
ping www.mcuzone.com -I eth0
ping www.mcuzone.com -I eth1
Priority can be checked by executing the route command; the network card with the smaller metric value will be preferred for communication.
We can also force communication through another network by disabling a specific network card. For example, to disable eth0, you can execute the following command:
sudo ifconfig eth0 down
And enable eth0 by the following command:
sudo ifconfig eth0 up
3.2.2 Set network adapter priority
To set the priority of network cards, you need to modify the metric value of the network card. First, we need to install the ifmetric software.
sudo apt install ifmetric
After the installation is complete, you can modify the metric value of the network card. If you need to change the metric value of eth0 to 102, you can execute:
sudo ifmetric eth0 102
After making the changes, use the route command to check, and we can see that the metric value of eth0 has been updated to 102:
However, this modification is only temporary; if the system is restarted, it will revert to its original state. To permanently change the metric value of eth0 to 102, you need to edit the startup file to achieve this.
Open rc.local by the following command:
sudo nano /etc/rc.local
Add the command you want to execute at startup above exit 0, such as sudo ifmetric eth0 102, then save the file. You can modify the metric of eth0 every time the system starts by this way.
After modifying the metric values, it is possible that the system's nameserver (i.e., DNS server) is still using the previous higher-priority network card's nameserver. Since the default network card has now changed, this can lead to domain name resolution issues. So we also need to update the nameserver.
Open resolv.conf by the following command:
sudo nano /etc/resolv.conf
Check if the current nameserver is correct. If it is not, please change it to the nameserver of the network card with higher priority or to some common nameserver addresses (such as 8.8.8.8, etc.).
3.2.3 Using udhcpc to specify DNS servers
In the previous section, we discussed specifying DNS servers by modifying the nameserver. In fact, we can also achieve this by using udhcpc.
Install the udhcpc software:
sudo apt install udhcpc
In this section, in the example we are testing, eth0 is a USB-to-Ethernet adapter, and eth1 is a 4G Cat1. If we need to use the network DNS of the USB-to-Ethernet adapter (eth0), please use the following command:
sudo udhcpc -i eth0
If we need to use the network DNS of the 4G Cat1 (eth1), please use the following command:
sudo udhcpc -i eth1
3.2.4 Examples of how to use udhcpc
Example 1: The 100Mbps Ethernet port is connected to the Internet, and the 4G Cat1 is connected normally. In this case, if we ping a certain domain name, it will succeed:
At this point, unplugging the 100M network port cable will make the ping fail:
Run sudo udhcpc -i usb0 and switch the DNS server to 4G Cat1, then you should be able to ping normally:
Example 2: The 100Mbps Ethernet port is connected to the internal network (not connected to the Internet), 4G Cat1 is connected normally. In this case, if we ping a certain domain name, it will failed:
Execute sudo udhcpc -i usb0, switch the DNS server to the 4G Cat1, and then you should be able to ping normally, and access internal network devices via the IP addresses:
3.2.5 Test speed by iperf3
You can download iperf3 (Windows version) in:
http://www.mcuzone.com/down/Software.asp?ID=10000634
Install iperf3 (Linux version) by using the following command:
sudo apt-get install iperf3
100M Ethernet speed test results: It is about 70Mbps in client mode and it is about 90Mbps in server mode:
Note: The USB to 100M Ethernet adapter may not reach full speed due to the performance limitations of the Zero 2W, the USB hub, and the bandwidth usage of the 4G Cat1.
4G CAT1 speed test results:
Note: Network speed tests are affected by network conditions and testing methods. The actual speed may vary; this test is for reference only.
3.3 AT Command for 4G
3.3.1 Open AT Command serial port
Taking CAT1ETH as an example, the same steps apply to the other 4G modules:
Execute commands in the terminal:
lsusb
Record the ID value of the 4G module: 19d1 0001
Use the following command to open the serial port, where the value after echo is the ID recorded above:
sudo modprobe option
sudo sh -c 'echo 19d1 0001 > /sys/bus/usb-serial/drivers/option1/new_id'
After execution is complete, the OS should have three additional devices: ttyACM0, ttyACM1, and ttyACM2. Input ls /dev to view:
▶ If it is RS485CAT1, the 4G serial device identified in the device is ttyUSB0-2.
▶ If it is RS485CAT1EU or CAT1ETH, the 4G serial device identified in the device is ttyACM0-2.
Install minicom:
sudo apt-get install minicom
Open AT Command serial port by minicom:
▶ If it is RS485CAT1:
sudo minicom -D /dev/ttyUSB0
(Note: Typically, three ports (ttyUSB0 to ttyUSB2）will appear. In general, the AT port is ttyUSB0 under most OSs. If that doesn't work, you may try other ports such as ttyUSB1. If multiple USB-to-serial devices are present, further attempts will be needed until the correct AT port is identified.)
▶ If it is RS485CAT1EU or CAT1ETH:
sudo minicom -D /dev/ttyACM0
(Note: Typically, three ports (ttyACM0 to ttyACM2）will appear. In general, the AT port is ttyACM0 under most OSs. If that doesn't work, you may try other ports such as ttyACM2. If multiple USB-to-serial devices are present, further attempts will be needed until the correct AT port is identified.)
The first time you enter an AT command, there may be no echo. If you then input the command at and press Enter, and it returns "OK," it indicates that everything is working properly. If you need to check the echo, please type the command: ate1, then press Enter. After that, you can continue to type other commands and see the inputs.
3.3.2 Common AT commands
1) Check if the SIM card is detected:
at+cpin?
Return ready to indicate the card has been recognized, if return error, you need to check the hardware.
2) Check antenna signal quality:
at+csq
Return values between 26 and 31 indicate a good signal, with 31 representing a full signal strength; return values between 20 and 25 indicate a barely acceptable signal; return values below 20 indicate a poor signal or that the antenna might not be connected.
3) Check network registration status:
at+cops?
Normally, it should return the network supporter's code: 7, where 7 represents 4G.
Note: The above command at+csq should not include a question mark, while the other two commands require a question mark.
4) View the SIM card's IMEI code:
at+cgsn
5) Reset 4G module (Sometimes, if you reinsert the SIM card, hot swapping may not work; in such cases, you can use this reset command to reset the module.):
at+reset
6) Disable radio frequency:
at+cfun=0
Enable radio frequency:
at+cfun=1
The two commands mentioned above can be used in pairs to allow the module to re-register with the network without restarting the 4G module.
3.4 RS485 serial test
The RPi0_RS485CAT1 expansion board comes with an RS485 module. This RS485 interface is converted from a USB channel and is independent of the Raspberry Pi Zero's native 40-pin GPIO. The operation of this RS485 interface is as follows.
First, you need to install the serial port software CuteCom; the installation command is:
sudo apt install cutecom
After installation, click on the Raspberry Pi icon in the top left corner of the desktop, and under "System Tools," there will be a shortcut to CuteCom:
If there are permission issues during use, please open the Raspberry Pi OS terminal and enter:
sudo cutecom
to run the CuteCom.
This expansion board comes with a 4G module.
▶ If it is RS485CAT1:
The 4G module occupies three serial ports, ttyUSB0 to ttyUSB2, so the RS485 serial port is shifted accordingly to ttyUSB3.
Execute in the terminal:
ls /dec/ttyUSB*
You can then see these 4 serial ports.
▶ If it is RS485CAT1EU or CAT1ETH:
The serial port number for the RS485 serial port is ttyUSB0.
Plug a USB to RS485 converter into the PC and connect it to the RS485 port on the expansion board. Open the serial port software on each end for transmission and reception. The result is as follows (Using ttyUSB3 as an example):
Raspberry Pi OS:■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■Windows:
Through practical testing, the baud rate can reach up to 2.06M (based on the criterion that transmitted data does not become garbled).
3.5 FAQ
Q: If the OS stop at the Raspberry Pi logo and fails to boot, or if after booting, the keyboard, mouse, and 4G module cannot be used, what can we do?
A: Please carefully check whether the pogo pins are aligned with the gold-plated contacts. Additionally, on the PC, open the config.txt file located in the root directory of the TF card to check the USB initialization script.
You need to confirm that the three red-boxed areas in the following image are all configured completely. If not, please manually add the missing parts and save the file:
# otg_mode=1 (It is recommended to comment out as follow)
dtoverlay=dwc2,dr_mode=host (These two areas must be ensured to be included.)
IV. Work with Ubuntu OS
The hardware in this document is based on the Raspberry Pi Zero 2W.
Ubuntu system: Ubuntu Server 24.04 LTS. (The Raspberry Pi Zero 2W cannot use the Desktop version due to performance limitations.)
The image is: ubuntu-24.04-preinstalled-server-arm64+raspi.img.xz
You can download the Ubuntu system in:
https://ubuntu.com/download/raspberry-pi
4.1 Edit the initialization script
After flashing Ubuntu Server, please open the config.txt file located in the root directory of the system partition on the TF card on your PC to check the initialization script for USB. Ubuntu Server initializes the USB twice, but the first initialization does not configure it in host mode. Please verify that the area highlighted in red in the following image is configured properly. If it is not, please manually add the complete configuration:
dtoverlay=dwc2,dr_mode=host
4.2 Configure username and password
Insert the TF card into Zero 2W and boot up the system. Upon the first startup, you will be prompted to log in; both the username and password are "ubuntu." After logging in successfully, you will be asked to change the password.
Once the password is changed, you will automatically enter the system.
4.3 Configure network
After system startup, there is no network available, and further configuration is needed before it can be used.
Note: the system does not integrate the ifconfig tool by default; only the ip command is available.
Execute ip addr to view and record the name of the network interface card:
The second network interface card (enx00e0996df1cd) is a USB-to-100Mbps Ethernet adapter, and the third network interface card (enxac4bb3b9ebe5) is the 4G module.
Then run the following command to open the network interface card configuration file:
sudo nano /etc/netplan/50-cloud-init.yaml
Edit the network interface card configuration file according to the diagram below:
Save and exit, then reset the system.
After rebooting, you can connect to the network. Install the net-tools to facilitate usage:
sudo apt install net-tools
4.4 Test network and 4G module
Run the command ifconfig -a to view the information of network:
The first network interface card is a USB-to-100Mbps Ethernet adapter, and the second network interface card is the 4G module.
By using the -I parameter, you can specify the network interface name when sending ping packets, thus determining which interface to use for the ping. Through ping tests to Tencent's website using these two network interfaces, we can know that the second network interface (4G module) supports IPv6:
4.5 AT command interaction test
▶ If it is RS485CAT1, the 4G serial device identified in the device is ttyUSB0-2.
▶ If it is RS485CAT1EU or CAT1ETH, the 4G serial device identified in the device is ttyACM0-2.
Install minicom:
sudo apt-get install minicom
Then, just like with the Raspberry Pi OS, first configure and enable the tty serial port, and then open the AT command serial port via minicom:
▶ If it is RS485CAT1:
sudo minicom -D /dev/ttyUSB0
(Note: Typically, three ports (ttyUSB0 to ttyUSB2）will appear. In general, the AT port is ttyUSB0 under most OSs. If that doesn't work, you may try other ports such as ttyUSB1. If multiple USB-to-serial devices are present, further attempts will be needed until the correct AT port is identified.)
▶ If it is RS485CAT1EU or CAT1ETH:
sudo minicom -D /dev/ttyACM0
(Note: Typically, four ports (ttyUSB0 to ttyUSB3）will appear. In general, the AT port is ttyUSB0 under most OSs. If that doesn't work, you may try other ports such as ttyUSB2. If multiple USB-to-serial devices are present, further attempts will be needed until the correct AT port is identified.)
The first time you enter an AT command, there may be no echo. If you then input the command at and press Enter, and it returns "OK," it indicates that everything is working properly. If you need to check the echo, please type the command: ate1, then press Enter. After that, you can continue to type other commands and see the inputs.
4.6 RS485 serial test
▶ If it is RS485CAT1:
The 4G module occupies three serial ports, ttyUSB0 to ttyUSB2, so the RS485 serial port is shifted accordingly to ttyUSB3.
▶ If it is RS485CAT1EU or CAT1ETH:
The serial port number for the RS485 serial port is ttyUSB0.
Plug a USB to RS485 converter into the PC and connect it to the RS485 port on the expansion board. Open the serial port software on each end for transmission and reception. We use minicom on Ubuntu OS (Using ttyUSB3 as an example):
sudo minicom -D /dev/ttyUSB3
Ubuntu OS:■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■Windows:
Through practical testing, the baud rate can reach up to 2.00M (based on the criterion that transmitted data does not become garbled).
V. Work with OpenWrt
5.1 Overview
This expansion board, when paired with the Raspberry Pi Zero 2W running OpenWrt, can be configured as a one-in-one-out switch mode. The 4G module on the expansion board can serve as the WAN port (for direct 4G internet access), while the Ethernet port is configured as the LAN port for connecting to a PC.
5.2 Preparation
The OpenWrt which be used in this document is: openwrt-bcm27xx-bcm2709-rpi-2-squashfs-sysupgrade-linux-6.1.98-20240723.img.gz
After flashing the OpenWrt system and powering it up, we connect an Ethernet cable from the Raspberry Pi's built-in Ethernet port to the PC's Ethernet port. Once the connection between the PC's network card and the Raspberry Pi's Ethernet port is successful, we find Network and Internet settings in Windows, then open the connected network under Ethernet to view the default gateway IP address. This address is the backend configuration page address for the OpenWrt system. As shown in the figure, the address for this test is 192.168.198.1:
Then open a web browser and enter 192.168.198.1 to access the OpenWrt system. The default username is root, and the default password is password.
5.3 Configure the OpenWrt system
After entering the OpenWrt system, connect the Raspberry Pi's Ethernet port directly to the PC's Ethernet port using an Ethernet cable. Once the PC's network card has acquired an IP address, the PC can directly access the internet through the 4G module (no additional settings required).
5.4 Test the network speed of 4G module
On the PC, open https://www.speedtest.cn/ to perform a speed test. At this point, the traffic goes through the 4G module, and the test results are as follows:
Note: The speed of 4G network testing is influenced by network signal strength and the testing method, so actual speeds may vary.
5.5 Mounting USB drive and file operations
When you insert a USB drive into a USB port, you can directly see the information and mounting status of the USB drive in "System - Disk Management":
In the "System - Mount Points" section, you can see the status of all mount points and can configure them on this page.
In the "Network Storage - File Assistant" section, you can perform operations on files within the system.
5.6 TTYD terminal
The OpenWrt system comes with a web-based TTYD terminal, which can be accessed in the "System - TTYD Terminal" section. The default username is root, and the default password is password. Since you log in with the root account, you will have root privileges upon logging in.
VI. Orange Pi Zero 2W test
The size and design structure of the Orange Pi Zero 2W are compatible with the Raspberry Pi Zero development board, making it suitable for our expansion board as well. This chapter introduces the use of the Orange Pi Zero 2W with the RPi0_RS485CAT1.
This test uses Ubuntu 24.04, and the version is: Orangepizero2w_1.0.4_ubuntu_noble_desktop_xfce_linux6.1.31.img.
You can download it in:
The OS is flashed onto the TF card.
Insert the USB keyboard and mouse into the expansion board. Open the terminal, enter lsusb, and the display is as follows:
6.1 Network test
Open the terminal, enter ifconfig -a, and the display is as follows:
It can be seen that the 4G module havs successfully obtained IP addresses.
Executing the route command displays the following:
Ethernet is ranked first, and we are connected to the internet via Ethernet.
We successfully ping both external IP addresses and domain names, indicating that the Ethernet is functioning properly:
If you want to use the 4G module for internet access, you need to set the priority of the 4G module to the highest, the steps are as follows:
Install the ifmetric software:
sudo apt install ifmetric
Then execute:
sudo ifmetric enxac4bb3b9ebe5 99
This sets the 4G module to the highest priority. After executing the route command, the 4G module will appear in the first position, enabling internet access through the 4G module:
4G module is ranked first, and we are connected to the internet via 4G module.
We successfully ping both external IP addresses and domain names, indicating that the 4G module is functioning properly:
6.2 RS485 test
After testing, it has been found that the braille software brltty in this OS occupies the ID of the USB-to-serial port (i.e., the RS485 serial port on the expansion board). Therefore, it is necessary to first block the occupied ID in brltty.
Execute in the terminal:
sudo nano /usr/lib/udev/rules.d/85-brltty.rules
Add a "#" before the following statement to comment it out:
ENV{PRODUCT}=="1a86/7523/*", ATTRS{idVendor}=="1a40", ATTRS{idProduct}=="0101", ENV{BRLTTY_BRAILLE_DRIVER}="bm", GOTO="brltty_usb_run"
Save and restart the OS.
Execute in the terminal:
ls /dev/ttyUSB*
ttyUSB0 is the RS485 serial port.
Install the serial port software CuteCom:
sudo apt install cutecom
Open CuteCom, select ttyUSB0, plug a USB-to-485 converter into the PC, and connect it to the 485 serial port on the expansion board. Open serial communication software on both ends for transmission and reception, with the results as follows:
Ubuntu OS:■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■■Windows:
Through practical testing, the baud rate can reach up to 0.41K (based on the criterion that transmitted data does not become garbled).
The method to open the AT command serial port is the same as in the Raspberry Pi OS. Execute the following in the terminal:
sudo modprobe option
sudo sh -c 'echo 1782 4e00 > /sys/bus/usb-serial/drivers/option1/new_id'
Execute the following after completion:
ls /dev/ttyUSB*
It can be seen that three additional serial ports, ttyUSB1-3, have appeared, which are the serial ports of the 4G module.
After testing, ttyUSB1 is identified as the AT command serial port. The remaining AT command operations are the same as those in the Raspberry Pi OS.
VII. Expansion board selection guide
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