Physical Layout & I/O
Pinouts, ports, indicators, and electrical characteristics for every externally accessible interface on the ALPON X4 industrial edge computer. Use this reference to wire the device, drive its GPIO from software, and plan field installations.
The ALPON X4 exposes 3 power inputs (USB-C PD, 9–30 V DC terminal, optional PoE+), 1× Gigabit Ethernet and 1× 100 Mbps Ethernet, 2× USB 2.0 (1 A shared), HDMI 2.0 for display up to 4Kp30, an RJ45 GPIO Add-on port (I²C / UART / SPI at 3.3 V logic), 4 LED indicators, 2 user buttons, and 2 DIP switches for watchdog and image-flash mode.
Raspberry Pi CM4 1× Gigabit + 1× 100 Mbps Ethernet 2× USB 2.0 HDMI 2.0 / 4Kp30 RJ45 GPIO 9–30 V DC PoE+ (variant)
Device layout
The ALPON X4 is housed in a fanless aluminum enclosure. All I/O is split between the front face (power, USB, display, indicators) and the rear face (Ethernet, GPIO, antennas, switches). Click any image to enlarge.
Front face
Rear face
Enclosure
Mechanical specifications
Need 2D drawings or mounting templates?
Mounting templates, hole patterns, and dimension files are on the Power & Mounting page.
Power input
The ALPON X4 accepts power from three independent sources. There is no hard priority between inputs: the device draws from the source with the highest voltage. The device must be operated with only one power input at a time; connecting two or more power sources simultaneously is not recommended.
USB Type-C (Power Delivery)
The USB-C port accepts power from a USB PD-enabled adapter capable of providing 27 W or more. We recommend using the power adapter included in the package.
| Recommended adapter | 27 W minimum at 15 V (USB PD) |
|---|---|
| Supported PD profile | 15 V / 1.8 A (27 W) |
| Mode | Sink only (no power output, no USB data during normal operation) |
| USB data | Available only while SW2 = Burn |
The USB-C port does not provide USB data or power output during normal operation. It operates in sink-only (power in) mode.
Screw terminal (9–30 V DC)
The recommended input for industrial deployments. Supplied with a 3-pin terminal block. Pay attention to the polarity (+ / −) when wiring.
| Input voltage | 9 V to 30 V DC |
|---|---|
| Minimum power | 27 W |
| Typical adapter | 12 V or 24 V DC, 30 W |
| Pinout (3-pin block) | Pin 1 Chassis Ground · Pin 2 Negative (−) · Pin 3 Positive (+) |
Power over Ethernet (PoE+)
PoE+ is available only on PoE-variant SKUs. The PoE+ module is built into the device and cannot be added separately. When present, PoE+ is wired to the ETH/G port; the 100 Mbps ETH port does not accept PoE.
| Standard | IEEE 802.3at · PoE+ Class 4 |
|---|---|
| Compatible adapters | PoE+ Class 4 only · passive PoE not supported |
| Supported port | ETH/G (Gigabit) only |
Power consumption
The ALPON X4 typically draws between 7 W and 14 W during normal operation, with a 27 W peak under full load. Consumption depends on workload, attached peripherals, and active radios.
| Typical draw | 7 W to 14 W |
|---|---|
| Peak draw | 27 W (workload and peripheral dependent) |
| USB output budget | 5 V at 1 A total across both USB 2.0 ports |
Ethernet ports
Two RJ45 Ethernet ports with different link speeds. Use both for WAN + LAN routing, dual-NIC redundancy, or isolating trusted and field segments.
ETH/G 1 Gbps PoE+
Gigabit Ethernet port. Carries PoE+ on PoE-variant SKUs.
ETH 100 Mbps
Native CM4 Ethernet port. 100 Mbps Fast Ethernet, no PoE.
On some PoE variants, the ETH/G port is replaced by the PoE+ port. Check your specific SKU before planning network topology.
USB 2.0 ports
Two USB 2.0 high-speed ports. Devices connected here are recognized as directly attached to the Raspberry Pi CM4 USB port. Both ports share a combined 1 A power budget.
| Standard | USB 2.0 High-Speed (480 Mbps) |
|---|---|
| Routing | Direct to Raspberry Pi CM4 USB controller |
| Shared power budget | 1000 mA total at 5 V across both ports |
| Overcurrent behavior | Power cut to both ports if 1 A is exceeded |
| Power recovery | Full device shutdown and power-on required |
You can connect a single device drawing up to 1 A, or two devices with a combined draw of no more than 1 A. If this limit is exceeded, power to both ports cuts off and a full device reboot is required to restore.
Display (HDMI 2.0)
Single HDMI 2.0 port driven directly by the CM4. Connects to a standard monitor with an HDMI cable. Supports up to 4K @ 30 Hz.
| Standard | HDMI 2.0 |
|---|---|
| Maximum resolution | 4K @ 30 Hz (4Kp30) |
| Audio | HDMI audio pass-through |
Display detection runs at boot. For first-time setup or headless-to-monitor transitions, plug in HDMI before powering the device.
GPIO Add-on port (RJ45)
The GPIO Add-on port provides the I/Os, supply voltage, and communication interfaces (I²C, UART, SPI) needed for ALPON Edge Add-on modules. The connector is a standard RJ45 socket but routes Raspberry Pi CM4 GPIO pins, not Ethernet.
Although the connector is RJ45, this port is not Ethernet and not PoE-capable. Connecting it to a switch, router, or PoE injector will cause permanent hardware damage. Use only with compatible ALPON Add-on modules.
The pins are not directly connected to the connector. To ensure greater stability for long connections, they are routed through a voltage-level converter before exiting the RJ45 socket.
Pin assignment
| RJ45 Pin | CM4 GPIO | Alternate functions |
|---|---|---|
| 1 | GND | Ground |
| 2 | GPIO 12 | SPI5_CSn[0], UART4_TX, I2C2_SDA |
| 3 | GPIO 14 | SPI5_SIO[0], UART0_TX, I2C3_SDA |
| 4 | GPIO 13 | SPI5_SIO[1], UART4_RX, I2C2_SCL |
| 5 | GPIO 15 | SPI5_SCLK, UART0_RX, I2C3_SCL |
| 6 | GPIO 23 | I2C3_SCL |
| 7 | GPIO 22 | I2C3_SDA |
| 8 | 5V OUT | 5 V output, max 1 A. Gated by GPIO 21 power switch |
Electrical characteristics
| Signal voltage | 3.3 V logic (level converter on board) |
|---|---|
| 5 V tolerance | Pins are not 5 V tolerant |
| Power output | 5 V at 1 A maximum (5 W) |
| Power switch enable | GPIO 21 · must be HIGH before I/O |
| Fault detection | GPIO 20 · HIGH normally, LOW on fault |
The voltage level of all pins is 3.3 V. Pins are not 5 V tolerant. Driving them above 3.3 V can damage the CM4.
Enabling the port from software
The 5 V supply and signal I/O are gated by an on-board power switch. Drive GPIO 21 HIGH to activate the port, then read GPIO 20 to confirm no fault is asserted.
| Signal | CM4 GPIO | Description |
|---|---|---|
ADDON_PWS_EN | GPIO 21 | Drive HIGH to activate the port. I/O is inactive while LOW. |
ADDON_PWS_FAULT | GPIO 20 | Reads HIGH normally. Goes LOW on overcurrent or short-circuit events. Returns HIGH once the fault clears. |
# 1. Enable the GPIO Add-on port power rail pinctrl set 21 op dh # drive GPIO 21 HIGH pinctrl get 20 # read fault line, expect 1 (HIGH)
RJ45-to-terminal block adapter
When optional RJ45-to-terminal block adapters are attached, the GPIO port pins are mapped to screw-terminal positions for easy field wiring.
LED indicators
Four LEDs on the front face report system state. The Programmable RGB LED is reserved for user applications. The remaining LEDs are driven by ALPON X4 OS and the Sixfab Connect agent.
All LEDs are driven through the TCA6408A I²C I/O expander at address 0x20 on the I²C1 bus (SDA: GPIO 2, SCL: GPIO 3).
| LED | Expander pin | Description | |
|---|---|---|---|
| Programmable RGB | P2 (R) · P3 (G) · P4 (B) | Freely programmable via GPIO. User-defined. | |
| Cellular Status | Driven by ALPON X4 OS | Red: poor signal · Yellow: moderate · Blue: good connection. | |
| Connection Status | Driven by Sixfab Connect agent | Lights green when the device is reachable via Sixfab Connect. | |
| Power | System power rail | Turns white about 3 seconds after the device powers on. |
The Programmable RGB LED is wired to expander pins P2 (Red), P3 (Green), and P4 (Blue). Set the corresponding pin LOW to turn that color on. A reference Python script that cycles through red, green, and blue is available as a GitHub Gist.
Push buttons
Two user-configurable hardware buttons. Both lines are pulled HIGH by default and read LOW while pressed. Both can be assigned to different functions in software.
| Button | CM4 GPIO | Default behavior |
|---|---|---|
| PB1 (front) | GPIO 5 | Pulled HIGH · LOW when pressed · user-defined action |
| PB2 (rear) | GPIO 6 | Pulled HIGH · LOW when pressed · user-defined action |
Watchdog & Boot/Burn switches
Two DIP switches sit under a silicone cap on the rear face. Both ship OFF by default and should remain OFF during normal operation. Use a pointed tool to lift the cap from its notch.
| Position | SW1: Watchdog | SW2: Boot/Burn |
|---|---|---|
| ON | Watchdog Inactive | Burn (image flash) |
| OFF (default) | Watchdog Active | Boot (operating mode) |
SW1 · Hardware watchdog
The hardware watchdog monitors device operation independently of the OS. When active (SW1 OFF), the device resets in case of failure. The watchdog runs on dedicated logic and cannot be disabled in software.
SW2 · Boot / Burn mode
SW2 selects between normal operation (Boot) and CM4 image flashing over USB-C (Burn). In Burn mode, the USB-C port exposes the CM4 flashing interface to a host PC.
The device must be completely powered off when switching between Boot and Burn modes. Both switches are set to OFF by default from the factory and no changes are needed during normal operation. If either switch has been changed, set both back to OFF before powering the device. Toggling switches in modes other than Boot and Burn can prevent the device from achieving maximum uptime.
If an image is damaged or needs reflashing, contact Sixfab support before attempting the flash. Trying to reflash the image without guidance may cause more issues.
Antenna connectors
Four SMA connectors on the side carry the wireless interfaces. Labels on the enclosure identify each port.
| Antenna | Label | Notes |
|---|---|---|
| LTE Main | L | Primary cellular RF path |
| LTE Diversity | L | Rx diversity for improved link budget |
| GNSS / GPS | G | Active antenna · must face the sky |
| Wi-Fi | W | 2.4 GHz + 5 GHz |
Need radiation patterns and certified bands?
LTE band list, antenna gain, and certified RF specifications live on the Connectivity & Antenna Specifications page.
Internal bus topology
How each external interface maps back to the CM4. Useful for diagnosing throughput limits and shared-rail behavior.
| Interface | CM4 connection | Notes |
|---|---|---|
| USB Port 1 + 2 | Native USB 2.0 | Direct to CM4 USB controller, 1 A shared budget |
| ETH (100 Mbps) | Native Ethernet MAC | Direct to CM4 Ethernet controller |
| ETH/G (1 Gbps) | USB-to-Gigabit bridge | Carries PoE+ on PoE variants |
| HDMI Display | CM4 HDMI 0 | 4Kp30 maximum |
| LEDs | I²C1 → TCA6408A @ 0x20 | Expander-driven |
| GPIO Add-on Port | CM4 GPIO 12–15, 22, 23 | Gated by GPIO 21 power switch |
| Buttons | CM4 GPIO 5 (PB1), GPIO 6 (PB2) | Pulled HIGH, LOW when pressed |
Updated 10 days ago