What is OPN?

OPN stands for the Open Pyro Network. This is an open-source specification for how to build an OPN-compatible PCB or system that can work with any pyrotechnics firing system that supports the OPN specification. To be clear, OPN is not restricted to just one firing system. Any system is allowed to implement the OPN specification, and anyone who wants to build an OPN accessory may do so. As long as the interface specification is followed it should work on any supporting firing system.

For example, OPN accessory boards already exist for:
    • Ethernet communications – this can be used instead of wireless or 2-Wire communications to run the show.
The OPN printed circuit board is approximately 100mm x 100mm in size and must contain three 12-pin header connectors in specified locations that connect the board to the OPN Bus. The OPN Bus is implemented in 36 pins, across three 12-pin connectors labeled J1, J2, and J3. The connector pinout is defined as:

CONNECTOR PIN PIN NAME DESCRIPTION
J1 1 +3.3V 3.3VDC Power line to Accessory Board. Max 200mA
J1 2 +3.3V
J1 3 MISO SPI bus master in slave out
J1 4 MOSI SPI bus master out slave in
J1 5 SCK SPI bus clock
J1 6 SCL I2C bus clock
J1 7 SDA I2C bus data
J1 8 GPIO0 General purpose IO 0
J1 9 GPIO1 General purpose IO 1
J1 10 GPIO2 General purpose IO 2
J1 11 GPIO3 General purpose IO 3
J1 12 GPIO4 General purpose IO 4
J2 1 VBAT Battery voltage 6.0 to 8.4VDC, 7.4V nominal 2A Max
J2 2 VBAT
J2 3 VSOURCE 12.7VDC Capacitor bank voltage source. Only activated when The system is ARMED
J2 4 VSOURCE
J2 5 /OPN1_INT OPN interrupt 1 (Active Low)
J2 6 /OPN2_INT OPN interrupt 2 (Active Low)
J2 7 GPIO5 General purpose IO 5
J2 8 GPIO6 General purpose IO 6
J2 9 GPIO7 General purpose IO 7
J2 10 GPIO8 General purpose IO 8
J2 11 UART2_TX Primary communications UART to host system. Default baud rate Is 115200 8-N-1
J2 12 UART2_RX
J3 1 GND Ground/common line for all voltages
J3 2 GND
J3 3 UART3_RX Communications UART to host system 115200 8-N-1
J3 4 UART3_TX
J3 5 /OPN3_INT OPN interrupt 3 (Active Low)
J3 6 /OPN4_INT OPN interrupt 4 (Active Low)
J3 7 ADC Analog to digital converter (Analog Voltage)
J3 8 ARM1 First ARM signal to host
J3 9 ARM2 Second ARM signal to host
J3 10 CONTINUITY Continuity enable signal to host
J3 11 FIRE Fire enable signal to host
J3 12 ILIMIT CREWSAFE® current limited voltage source
In communication with the Host, there are two types of system messages, push requests and pull requests. Some data, like changes in system status from Safe to Arm, are pushed to the accessory when they happen. The accessory may also request information from the Host with a pull request. Action requests may be sent from the accessory to host at any time, and are generally in the form of:
  • Graphical User Interface (GUI) commands – These are a group of messages that can print text and simple graphics to the display screen, and request the button presses on the user interfaces be transmitted to the accessory. The accessory’s display screen is always updated by the action request, but the screen would only be visible when the OPN button is pushed on the CM or the OPN mode is selected on the FM.
  • System Control Commands – These commands allow an external system to essentially control the Command Module as if someone were pushing the buttons on the user interface.
  • System Identification Commands – When the system first powers up, a series of commands may be sent to the host identifying the accessory to the system and requesting services. If no identification or services are requested, the default is the UART2_RX and TX lines are available.
For a full specification of the OPN system, or if you would like to be involved in the definition and evolution of the OPN specification, please contact us at Info@Firelinx.com.
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