Physical Layout & I/O

Pinouts, ports, connectors, and indicators on the ALPON X4 industrial edge computer. This reference covers every externally accessible interface, its electrical characteristics, and the GPIO mapping required to drive it from software.

Device layout overview

The ALPON X4 enclosure is a fanless aluminum case measuring 111.16 × 99.9 × 33 mm, weighing approximately 457 g, rated IP40, and designed for -20°C to +60°C ambient operation. All I/O is distributed across the front and rear faces; the top face doubles as a passive cooling surface.

Front face (1–6)

Rear face (7–11)

Enclosure (12–14)

Mechanical specifications

Download the full 2D dimensional drawings for CAD integration: ALPON X4 Dimensions (PDF).

Power input

The ALPON X4 accepts power from three independent interfaces. Only one input should be connected at a time.

1. USB Type-C PD input

Sink-only USB-PD port. The device is powered by a USB PD-enabled Type-C adapter capable of delivering 27W or more. Use the adapter included in the package for guaranteed compatibility.

2. Screw terminal block (9–30V DC)

3-pin removable terminal accepting a wide DC input range for industrial power rails. Minimum supply rating: 30W at 12V or 24V. Observe polarity markings (+ / –) on the housing when wiring.

3. Power over Ethernet (PoE+)

Available only on PoE-variant SKUs. The PoE+ module cannot be added retroactively. PoE+ input is routed exclusively through the ETH/G port on PoE variants.

Ethernet ports

The ALPON X4 provides two Ethernet interfaces with distinct link speeds. Both ports use standard RJ45 connectors with integrated link/activity LEDs.

USB ports

Two USB 2.0 High-Speed ports on the front face, connected directly to the Raspberry Pi CM4 USB controller. Ports are enumerated as native CM4 USB devices by the host OS.

Display (HDMI)

Full-size HDMI 2.0 output routed from the CM4's primary display controller. Compatible with standard HDMI cables to any HDMI monitor or capture device.

GPIO Add-on port (RJ45)

The GPIO port exposes six configurable CM4 pins over an RJ45 connector, providing I²C, UART, and SPI to ALPON Edge Add-on modules. Signals are routed through a voltage-level converter for stable long-cable runs, with built-in ESD protection.

Pin assignment

Electrical characteristics

Power-switch control

The port's 5V supply and all signal I/O are gated by an on-board power switch. At boot, the port is inactive by default. To activate the port, drive GPIO 21 HIGH from software before any communication begins.

import RPi.GPIO as GPIO
 
GPIO.setmode(GPIO.BCM)
GPIO.setup(21, GPIO.OUT)   # ADDON_PWS_EN
GPIO.setup(20, GPIO.IN)    # ADDON_PWS_FAULT
 
# Enable the GPIO Add-on port
GPIO.output(21, GPIO.HIGH)
 
# Check for fault condition
if GPIO.input(20) == GPIO.LOW:
    print("Fault detected on Add-on port")

If an overcurrent, overtemperature, or reverse voltage condition is detected on the 5V rail, the port enters protection mode. GPIO 20 reads LOW while the fault persists and returns HIGH once the condition clears.

LED indicators

The ALPON X4 has four LED indicators on the front face. One RGB LED is reserved for user applications; the remaining three are driven by the ALPON Cloud platform and firmware-level services.

RGB LED control (I²C)

The RGB LED is driven by the TCA6408A I/O expander, connected to the CM4 on the I2C1 bus (GPIO 2 SDA, GPIO 3 SCL). The chip address is 0x20.

Reference implementation: RGB LED Python script on GitHub Gist.

Push buttons

The ALPON X4 provides two user-configurable hardware buttons. Both are wired to the CM4 GPIO with internal pull-up resistors, so each GPIO reads HIGH while the button is released and pulls LOW when pressed.

import RPi.GPIO as GPIO
 
GPIO.setmode(GPIO.BCM)
GPIO.setup(5, GPIO.IN, pull_up_down=GPIO.PUD_UP)   # PB1
GPIO.setup(6, GPIO.IN, pull_up_down=GPIO.PUD_UP)   # PB2
 
def on_pb1(channel):
    print("PB1 pressed")
 
GPIO.add_event_detect(5, GPIO.FALLING, callback=on_pb1, bouncetime=200)

Watchdog & Boot/Burn DIP switches

Two DIP switches on the rear face control the hardware watchdog and the CM4 boot mode. Both ship OFF by default and should remain OFF during normal operation. The switches are covered with a silicone cap; use a pointed tool to gently lift the cap from its notch.

SW1 – Hardware watchdog

The hardware watchdog monitors system liveness independently of the operating system. When enabled (SW1 OFF), the CM4 must toggle the watchdog trigger line at regular intervals. If no trigger arrives within the timeout window, the watchdog cuts all power to the device, waits briefly, then re-applies power to force a cold reboot.

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's flashing interface to a host PC running rpiboot.

Antenna connectors

Four SMA connectors on the top face provide external antenna access for cellular, GNSS, and Wi-Fi / Bluetooth radios. All connectors are standard SMA female; compatible with the bundled antennas or third-party antennas with SMA male terminations.

I/O topology

The ALPON X4's interfaces attach to the Raspberry Pi CM4 through native SoC controllers and a small number of bridge chips. The table below summarizes the primary data paths.

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