Wireless Launchpad Part 3: State Machine

The Pad will be the ultimate controller of state, managing exactly what mode it is in at any one time, and which states it is allowed to transition into.

The Remote will mirror this logic, but the system is not reliant on the Remote to properly maintain and permit state transitions. The Pad will be in constant communication with the Remote to tell it what state it is in. Should the Remote issue an invalid command the Pad will protect against this. Any unexpected command received by the Pad will cause the Pad to disarm itself and revert back to its base Disarmed state.

Functional Overview

The system can be in one of 4 states at any one time;

  • Disarmed
  • Armed
  • Continuity-Test-Passed
  • Firing

These stages must be entered into sequentially, as represented by the below state diagram.

Note that this diagram does not detail the logic governing the permissability of any state transition, it simply describes the set of possible states and transitions between them.

State Transitions and Logic

Arming

The system can only enter the Armed state if the physical Safety Interlock is engaged at the Pad. The system remains in an Armed state for 20s, after which it reverts to a Disarmed state should it not receive a valid Continuity Test command beforehand. When in an Armed state:

  • a physical indicator light at the pad is illuminated (Armed)
  • a warning siren sounds at the pad
  • a virtual indicator is shown on the Remote
  • the Remote is allowed to issue a Disarm and/or Continuity Test command

Performing a Continuity Test

A continuity test of the electrical ignition system (Ignitor) can only be performed when the system is in an Armed state. A continuity test can only be performed from the Remote. For saftey there is no physical continuity test mechanism at the Pad. If the continuity test fails, the system immedately reverts to a Disarmed state. If the continuity test passes, the system transitions to the Continuity-Test-Passed state.

Continuity-Test-Passed

The system remains in an Continuity-Test-Passed state for 20s, after which it reverts to a Disarmed state should it not receive a valid Fire command beforehand.

When in a Continuity-Test-Passed state:

  • a physical indicator light at the pad is illuminated (Ready)
  • a warning siren sounds at the pad
  • a virtual indicator is shown on the Remote
  • the Remote is allowed to issue a Disarm and/or Fire command

Firing

The system can only enter the Firing state from the Continuity-Test-Passed state. The system remains in the Firing state for at most 3s. Whilst in the Firing state, a continuity-test is performed to detect ignition. Which ever occurs first, Igniter continuity-failure or 3s elapsed, triggers the system to disarm itself into the Disarmed state. Whilst in the Firing state:

  • a physical indicator light at the Pad is illuminated (Firing)
  • a warning siren sounds at the Pad
  • a virtual indicator is shown on the Remote
  • the Remote is allowed to issue a Disarm command

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