Open Access v4 Specs and Ratings

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Electrical Specs and Ratings


  • 11-14VDC input, 1.5A self-resetting fuse
  • 5V, 2A (absolute max) PSU on-board.
  • 2x200ma 12V accessory power ports (fused)
  • 2x200ma 12V RFID reader supplies (fused)
  • 5V power available on RPi and LCD expantion ports (unfused)


  • Power: 5.00mm Phoenix screw terminal
  • Alarm, RS485, Relays: 3.50mm Phoenix screw terminal
  • Jumpers: .100
  • ICSP: 2x3 .100
  • RPi: 2x3 .100
  • LCD: 2x8 .100


  • 4x1FormC Relays, rated to 5A at 30VDC or AC.
    • Pinout: NO-Common-NC

Alarm Inputs

  • Support analog input via Analog 0..3 pins
  • Uses a 2.2K current-limited resistor, TVS diode for protection
  • Has a 10K pull-up resistor to +5V
  • Pinout: 1. Input 2 Ground
  • Usable sampling range: 0-4.1VDC. The protection and pull-up circuit form a 10K/2.2K divider.
  • Additional "Tamper" zone, which is a digital input, same configuration

RFID Inputs

  • Standard Wiegand26 inputs (GND, +12V, D0, D1, LED, Buzzer)
  • Same 2.2K/10K protection as Alarm inputs
  • D0,D1 pins are interrupt-driven (uses PCATTACH library for additional interrupt support)
  • 2.2K current-limited on LED/buzzer outputs


  • Atmega328P at 16.00Mhz
  • Comes pre-loaded with Arduino Bootloader
  • Compatible with "Duemillenova" Arduino
  • Uses FTDI FT232L USB chip and mini-USB
  • Includes ICSP header (6-pin) and reset switch


  • On-board hardwre RS485 chip (TI SN65HVD)
  • Connected to D6 (EN), D7 (RX), D8 (TX).
  • Use with SoftwareSerial library for interactive readers, chaining boards together in a bus

Real-time clock

  • DS1307 RTC with CR-2032 backup battery
  • 5 year+ battery life

Further Details