Interlocks are especially interesting when they have to be integrated with software.
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.
Type systems, database normalisation, reactive programming (i.e.: non-manual state management), or more generally making illegal states unrepresentable are the software equivalents!
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
> In modern days, most cars have an anti-theft feature that restricts the turning of the steering wheel if the key is not inserted in the ignition
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.
It’s a lemon market, as a car buyer there are no outward telling features whether the keyless entry system is susceptible to repeater attacks (most new cars still are), whether just anyone briefly inside the car can register new keys, whether it uses strong crypto, or whether a couple grand buy you a master key that unlocks and puts into drive most cars of a brand (famously Kia/Hyundai to this day, who also have all of the other vulnerabilities). Car reviews don’t mention any of these things, even when they are definitely known and tested (rarely) by some third parties. Strangely, not even the OEMs who have secure systems use them for advertising.
Are there any car brands which don't do this fancy-useless-tech kind of thing? I have never driven a car, but a motorcycle with handle-lock would never be unlocked without the physical key.
Interlocks are especially interesting when they have to be integrated with software.
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.
Type systems, database normalisation, reactive programming (i.e.: non-manual state management), or more generally making illegal states unrepresentable are the software equivalents!
> Defeatable interlocks are allowed on electrical equipment up to 600 volts.
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.
> In modern days, most cars have an anti-theft feature that restricts the turning of the steering wheel if the key is not inserted in the ignition
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.
It’s a lemon market, as a car buyer there are no outward telling features whether the keyless entry system is susceptible to repeater attacks (most new cars still are), whether just anyone briefly inside the car can register new keys, whether it uses strong crypto, or whether a couple grand buy you a master key that unlocks and puts into drive most cars of a brand (famously Kia/Hyundai to this day, who also have all of the other vulnerabilities). Car reviews don’t mention any of these things, even when they are definitely known and tested (rarely) by some third parties. Strangely, not even the OEMs who have secure systems use them for advertising.
Are there any car brands which don't do this fancy-useless-tech kind of thing? I have never driven a car, but a motorcycle with handle-lock would never be unlocked without the physical key.
I see no point in becoming a luddite given the availability of secure solutions. Keyless entry is great, it just has to be secure (d'uh).
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