Interlock (Engineering)

For safety, you want the interlock to be performed in hardware (what if SW crashed?) but at the same time, the software should be informed that the interlock is active. e.g., the operator opens the door while the machine is moving. A hardware switch should stop the motion, and the software controller must be told that the door is open and take appropriate action.

The fun part comes in when the interlock is implemented as a hardware switch that turns off power to everything (this is the easiest way to do it!) except the main CPU and then at the last minute, when software is close to completion, inform the software team that "oh, by the way, you have to respond to this interlock triggering at any time during operation and recover gracefully." So now, the first indication that the operator opened the door is that the subsystem you were talking to over a communication link is no longer responding. Is it a comms error? Did the subsystem crash or reset? Or did the user open the door and the interlock powered off the subsystem? Who knows? Just Do the Right Thing.

Fun fact, "high voltage" starts at 600v according to many regulatory bodies. 1kv is another popular threshold.

The blast pressure from an arc can get to a point where protective gear is irrelevant. Copper expands something like 30000x when it vaporizes.

    E - Establish (Identify all sources)
    S - Switch (Disconnect)
    V - Verify (Visually check, if possible)
    R - Release (Stored energy)
    L - Lockout/Tagout
    T - Test (Absence of voltage)
    G - Ground (If necessary)
    Renergize - Re-energizing Equipment

This needs updating:

> In the past, most cars had an anti-theft feature that restricted the turning of the steering wheel if the key was not inserted in the ignition. These days, for convenience, is enough that the key has been in the vicinity of the car in the recent past.