waveshareSIM7000G NB-IoT/Cat-M/Edge/GPRS HAT, Compatible with Raspberry Pi 5/4B/3B/Zero/Zero W/Zero 2W/Pico/Pico W/Pico WH, GNSS Positioning, Global Band Support

Bottom line up front: this is a great module for LTE Cat M1 / NB-IoT communication and works well with a Raspberry Pi using either the GPIO UART to establish a PPP "dial-up" connection. It also works great using USB instead of the GPIO UART.Key detail: this module uses only LTE Cat M1, NB-IoT, or 2G GPRS (which is no longer available in the US from any carrier). That is *not* your standard "4G LTE" service that you'd use with your phone. Cat M1 and NB-IoT are narrowband (read: not very fast) protocols intended for IoT ("Internet of Things") devices -- think utility meters, industrial monitoring and control systems, vehicle telemetry, etc. instead of smartphones. Those protocols offer slower maximum speeds (~1 Mbps with Cat M1, 10s of kbps with NB-IoT) in exchange for much longer range and wider coverage than typical smartphone service, as well as cheaper prices. You'll need to get a SIM card from a carrier like 1NCE, Hologram, etc. rather than a retail SIM card that you'd use in a smartphone.If that sounds like something you're interested in, this device is great.Pros:1. Product includes the "hat" itself that fits on the Raspberry Pi GPIO pins, a small antenna for the cellular connection (SMA connector), a u.fl-to-SMA pigtail for the GPS antenna, and a magnetic-mount active GPS antenna.2. All the supporting hardware (e.g. power regulators, capacitors, level shifters, connections for the UART, SIM card holder, etc.) are on the board already. It's pretty much plug-and-play. When connected to a Raspberry Pi 40-pin header, it will get its needed power from the GPIO pins and its onboard UART will be connected to the Pi's UART TXD/RXD pins in the proper way. It also includes little standoffs so you can mount it in some other enclosure without having to attach it to a Pi.3. It has several optional solder jumpers that let you configure the I/O voltage (5V or 3.3V, default 3.3V) for the UART, power-on behavior (either switched by a Pi GPIO pin or always-on, default is always-on), and behavior of the DTR pin (either switched by a GPIO pin or not connected, default is not connected) for the Pi to command the device to "hang up" a connect.4. A useful pair of LED lights lets you immediately see the power and connectivity status of the device at a glance.5. It has a built-in multi-system GPS receiver that can receive GPS (US), GLONASS (Russia), Beidou (China), and Galileo (EU) satellite navigation signals. The power to the GPS receiver is switchable and the receiver configurable via the UART interface using Hayes-type AT commands. You can configure to use any combination of GPS, GLONASS, Beidou, and Galileo (including all four), but using GPS is mandatory. You can turn off all the other constellations except GPS.6. It uses simple Hayes-type AT modem commands to control the device and connect to the network. It supports standard 3GPP TS 27.007 and 27.005 AT commands, and so will work fine with typical Linux "chat" and "pppd" programs to establish a PPP connection to the network. It also supports extended Simcom AT commands (Simcom being the manufacturer of the modem chip) that allows for some additional features, like the GPS receiver, to be controlled using AT commands.7. With a SIM card installed and the board powered up, it will automatically connect to and register with the mobile network. You just need to send commands to establish a "PDP context" (that is, a data connection). This connection can be a simple, one-shot connection to send message over one or more TCP or UDP packets to a remote system and then immediately disconnect (it has simple AT commands for sending such packets and providing the data payload to send), or you can establish a long-lived PPP connection and send arbitrary IP data (like connecting to the internet with a modem).8. The "G" model (which this is) supports all global Cat M1 and NB-IoT frequency bands and can be used globally (assuming your network provider allows global roaming). The "A" model only supports the bands commonly used in North America, the "E" model supports those used in Europe and certain other regions, and the "C" model supports those used in China. The "G" model is the way to go.9. It does not require USB drivers on modern Raspbian devices and correctly shows up as several serial ports (one for receiving GPS NMEA data, one for sending/receiving AT commands or setting up a PPP connection, and the other two are apparently for audio and diagnostics (which the manual doesn't go into detail about). It also connects to the Pi's GPIO UART directly, so you can interact with and use it for PPP using only the GPIO UART without having to use USB at all.Cons:1. Its board layout doesn't allow any other hats to be mounted on top of it. If you use several hats in a stack, this one needs to be on top since it doesn't have any male pins sticking up.2. The u.fl connector for the GPS antenna is tiny and requires a pigtail. The board is already pretty tightly packed, so I understand, but it would have been nice if they had a second SMA connector for a GPS antenna.3. The manual and wiki have useful information (especially the list of AT commands), but are very sparse, written in sometimes hard-to-understand English, and don't go into a lot of useful detail as to what various commands mean or how to perform various functions. Fortunately, since the device uses 3GPP-standard AT commands, the pppd daemon available on Linux (such as Raspbian, used on the Raspberry Pi), it's straightforward to adapt the default "gprs" pppd profile with only a few minor changes (like specifying the baudrate, serial port, etc.). Be prepared to search online to answer specific technical issues or get example configurations.4. The antenna positioning means the hat might not fit in every Raspberry Pi case, and may require some modification of the case. Alternatively, external antennas with a longer cable might allow the use of the hat without needing to modify the case, but I haven't tested this.As you can see, the pros easily outweigh the cons.In my specific case, I wanted to use it as a low-speed, last-resort backup management interface for connecting to a Pi that's located in a physically remote and hard-to-access location. The network connection in that area goes down occasionally, so having a cellular network link (even if it is very limited in terms of speed) to which I can connect using SSH makes diagnosing and fixing those issues much easier than having to travel there. I have pppd set up to establish a persistent connection which allows me to remotely access it at any time. The hat has maintained that connection for several days without interruption, and when intentionally interrupted (like when I replace the antenna with a dummy load and then reconnect the antenna) it reliably reconnects automatically.Put simply, this is a somewhat specalized device, but it's simple, low power, and performs its intended job very well.