Permanent Way Module Hardware


The P-Way module is designed to utilise a single microcontroller for most of its digital functionality. The rest of the circuit is principally power conversion, protection and interfacing.

The power domain starts with an external 24 - 36VDC supply. This is polarity protected and fused at 4A with a polyswitch. This is dropped to 14VDC with a switcher for driving rails, point frogs and accessories. This in turn is dropped to 5V for driving servos, and to 3.3V for most of the circuitry.

Major Components

Microcontroller - ST STM32F427

  • ARM Cortex-M4 @ 168MHz
  • 2MB Flash, 256MB RAM
  • SDIO memory card interface
  • SPI for display
  • Timers for rotary decoding
  • PWM for servo positioning
  • Ethernet MAC
  • UART for WiFi & console
  • ADCs for current measurement
  • GPIOs and hardware timers for bit banging DCC
  • GPIOs for everything else


  • 29x29mm OLED
  • 128 x 128 resolution
  • 18-bit colour
  • SSD1351 controller on SPI

Form Factor