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Hardware Reference

This page provides the electrical, mechanical and environmental specifications for HALPI2. For procedural information (installation, maintenance, replacement), see the Hardware Guide. For interface protocol details, see Interfaces and Connectivity.

Specifications Summary

Parameter Value
Compute module Raspberry Pi CM5 (CM4 compatible)
Carrier board controller RP2040 (Arm Cortex-M0+, dual core, 133 MHz)
Input voltage 9–36 VDC (absolute max 38.6V, transient protection to 100V)
Power consumption 250 mA idle to 590 mA under load (12V input, HaLOS headless)
Current limit settings 0.9A or 2.5A (selectable)
Supercapacitor backup 4× 25F / 2.7V in series (6.25F effective at 10.8V max)
Operating temperature −20°C to +60°C
Enclosure dimensions 200 × 130 × 60 mm (excluding connectors)
Enclosure weight TODO
Enclosure material Powder-coated die-cast aluminium
Ingress protection IP65
License CERN-OHL-S v2 (hardware)

Electrical Specifications

Power Supply

The power supply accepts a wide DC input range and provides regulated 5V and 3.3V rails for the CM5 and peripherals. Input protection includes reverse polarity protection (LM74800), overvoltage disconnect at 38.6V, TVS clamping, and common-mode/differential EMI filtering.

Parameter Value
Recommended input voltage 9–36 VDC
Absolute maximum input voltage 38.6V (continuous), 100V (transient, TVS-limited)
Maximum input current 0.9A or 2.5A (selectable current limiter)
Input fuse 7A (fault protection only)
10V intermediate rail 10.25V nominal (SiC463ED buck converter)
5V rail 5.1V / 4A (TPS566238, powers CM5 and USB ports)
3.3V rail 3.33V / 3A (TPS566238, controller-toggled on v0.6.0+)
3.3V UVLO threshold 4.5V supercap
Early 3.3V LDO SE8633K2 (for controller and supercap balancer startup)

Supercapacitor Backup

The supercapacitor bank provides backup power for graceful shutdown during power loss.

Parameter Value
Configuration 4× 25F / 2.7V cells in series
Effective capacity 6.25F at 10.8V maximum
Balancing Active balancing
Charge voltage range 0–10.8V (monitored by controller ADC)
Power-on threshold 8.0V (firmware-configurable)
Power-off threshold 5.5V (firmware-configurable)

Current Consumption

Measured at 12V input with a Raspberry Pi CM5 running HaLOS headless image.

Condition Current draw
System idle ~250 mA
Typical load ~400 mA
Peak load ~590 mA

Note

These measurements exclude external USB device consumption. Each USB 3.0 port can supply up to 0.93A, so total system draw depends heavily on connected peripherals.

Connector Pinouts

Power Input Connector

Phoenix MC type, 3.81 mm pitch, 2-pin. On the front panel, the E7T barrel connector connects to this header.

Pin Function
1 GND
2 VIN (9–36 VDC)

CAN FD Connector

Phoenix MC type, 3.81 mm pitch, 4-pin. Galvanically isolated.

Pin Function
1 GND_CAN (isolated ground)
2 —
3 CAN_H
4 CAN_L

The termination jumper (label "120R") enables a 120Ω termination resistor between CAN_H and CAN_L.

RS-485 Connector

Phoenix MC type, 3.81 mm pitch, 5-pin. Galvanically isolated.

Pin Function
1 GND_RS485 (isolated ground)
2 RX_A_C
3 RX_B_C
4 TX_A_C
5 TX_B_C

Button Header

2×3 pin header, 2.54 mm pitch. Each button pair is GND + signal.

Pin pair Function
Power CM5 power button (double-click = shutdown, long press = force off)
Reset RP2040 hardware reset (RUN pin)
User User-configurable (pending firmware implementation)

HDMI Connectors (HDMI0, HDMI1)

20-pin horizontal FPC connectors, 0.5 mm pitch (FPC0.5-SMT-20P). Each channel has ESD protection (RCLAMP0524P) and current-limited 5V supply (AP2553W6-7).

MIPI CSI/DSI Connectors (MIPI0, MIPI1)

22-pin horizontal FPC connectors, 0.5 mm pitch. Each channel has ESD protection (RCLAMP0524P). Compatible with Raspberry Pi camera and display modules.

M.2 NVMe Slot (PCIe M.2 M-key)

M.2 Socket M for NVMe SSDs, supporting 2230 through 2280 form factors. Connected via PCIe Gen 2 x1. Includes a dedicated SUSCLK oscillator for NVMe suspend/resume compatibility (added in v0.6.1).

Fan Connectors (CM5 Fan)

4-pin PWM fan connectors (HC-1.0-4PLT) available on both top and bottom sides of the carrier board. Connected in parallel — use only one at a time.

Pin Function
1 +5V
2 FAN_PWM
3 FAN_TACHO
4 GND

USB 3.0 Ports

Connector Connection Current limit
USB3-0 Direct to CM5 USB 3.0 0.93A (AP22652W6-7)
USB3-1-0 USB3 hub port 1 (UPD720210) 0.93A
USB3-1-1 USB3 hub port 2 0.93A
USB3-1-2 USB3 hub port 3 0.93A

All ports have ESD protection (RCLAMP0524P) and ferrite bead filtering.

Controller USB Port (MCU USB)

Micro-USB receptacle, USB 2.0 peripheral mode only. Used for RP2040 firmware updates (UF2 flashing). ESD-protected (RCLAMP0524P).

USB Boot Port (USB Boot)

USB Type-C receptacle, USB 2.0 peripheral mode. Connected to the CM5's USB 2.0 OTG port for USB mass storage booting. ESD-protected (RCLAMP0524P).

40-Pin GPIO Header (Raspberry Pi GPIO Header)

The GPIO header follows the standard Raspberry Pi 40-pin layout. The following pins are used by HALPI2's onboard peripherals:

GPIO Pin Function Interface Shared?
2 3 I2C1 SDA System I2C Yes (address 0x6d reserved)
3 5 I2C1 SCL System I2C Yes (address 0x6d reserved)
6 31 SPI0 CS CAN FD controller Custom CS — can coexist with standard CS pins
9 21 SPI0 MISO CAN FD controller Shared SPI0 bus
10 19 SPI0 MOSI CAN FD controller Shared SPI0 bus
11 23 SPI0 SCLK CAN FD controller Shared SPI0 bus
12 32 UART4 TX RS-485 Free if RS-485 disabled
13 33 UART4 RX RS-485 Free if RS-485 disabled
24 18 RS-485 EN RS-485 (manual mode) Free in auto mode
26 37 CAN INT CAN FD controller No

All remaining GPIO pins are available for HATs and user applications. See the Hardware Guide for HAT compatibility details and instructions for disabling built-in interfaces.

I2C Devices

The system I2C bus (I2C1, GPIO 2/3) hosts the following devices:

Address Device Function
0x4b TMP112A Board temperature sensor
0x6d RP2040 Carrier board controller (secondary mode)

The controller I2C bus (I2C0, internal to carrier board) is used for HDMI DDC and MIPI display communication, with 2.2kΩ pull-ups.

Isolation Architecture

The CAN FD and RS-485 interfaces are galvanically isolated from the rest of the system. Each interface has independent isolated power (B0505S-1WR3 DC-DC converter) and signal isolation.

Interface Signal isolation Power isolation Isolated ground
CAN FD ISO7121DR B0505S-1WR3 GND_CAN
RS-485 TI41M31 B0505S-1WR3 GND_RS485

This means bus faults, ground loops and noise on the CAN or RS-485 networks cannot damage or interfere with the main system.

Mechanical Specifications

Enclosure

Parameter Value
Material Powder-coated die-cast aluminium
Dimensions 200 × 130 × 60 mm (excluding connectors)
Weight TODO
IP rating IP65
Internal clearance above carrier board 45 mm (accommodates up to 2 stacked HATs)
Lid screws 4× M4×10 countersunk, PH2 head
Gasket Lid gasket for weather sealing
Pressure equalization Breather plug (must not be removed)

Panel Positions

The front panel includes pre-drilled positions for:

  • 1× E7T power connector
  • 1× NMEA 2000 Micro-C connector
  • 1× RJ45 Ethernet
  • 2× HDMI Type-A
  • 2× USB 3.0 Type-A
  • 1x RP-SMA antenna connector (for Wi-Fi/Bluetooth)
  • 2× SMA antenna positions (shipped with blind plugs)
  • 1× Breather plug
  • 3× PG7 cable gland positions (shipped with blind plugs)

Mounting

  • Carrier board mounting: 4x M4x6 screw-mounted to enclosure base
  • HAT mounting: 4× M2.5 threaded inserts (v0.5.0+; v0.4.0 requires manual nut installation)
  • CM5 mounting: 4× M2.5 solder nuts

Thermal Management

The CM5 is mounted on the underside of the carrier board. Heat is transferred from the CM5's SoC and RP1 chipset through thermal pads to the aluminium enclosure base, which acts as the heatsink.

Component Thermal pad thickness
SoC (BCM2712) 1 mm
RP1 2 mm
Power supply components 2 mm

The standard enclosure provides passive cooling without a fan. A 4-pin PWM fan connector is available for custom enclosures or high-ambient-temperature applications.

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