Lorin Hochstein

Ramblings about software, research and other things

There is no toggle lock signal

leave a comment »

Since I now work within walking distance of the house, our family downsized from two cars to one, with the expectation that we could use zipcar for those times when we both need a car.

Today was the first time I used the service, and I was pretty impressed with how well the workflow was thought out. A number of my questions about the service were quickly answered. (“How do you get in the car? There’s a scanner on the windshield that senses your Zipcard. Where do they put the keys so they don’t get lost? Keys are attached to a zipline mounted near the ignition. What about gas? There’s a debit gas card that lives in a special sleeve in the driver’s visor. How do they prevent gas card fraud? When you use the card, the pump requires you to input for your mileage and your zipcard number.”)

The first time I left the car, I locked it using the normal power door lock. When I tried to get back in by scanning my card, it locked the doors again instead of unlocking them. I swiped again, and I was in.

Why did scanning my card the first time lock the doors again? I don’t know for sure how the scanner mechanism is implemented, but I can take a guess. The scanner can send a “lock” or an “unlock” signal to the car, just like a regular key fob. However, it has no way to query the car for the state of the lock, so it has to keep the state of the lock’s internally. The first time I swiped my card, the scanner was in the “doors are locked” state, so it sent the unlock signal and switched to the “doors are unlocked” state. When I got out of the car and locked it with the power lock, the Zipcar scanner was still in the “doors are unlocked” state. When I came back and swiped, it thought the doors were unlocked and so it sent the “lock” signal and switched to the “doors are locked” state.

This problem could be avoided if the car could receive a “toggle lock” signal in addition to “lock” and “unlock”. In that case, the scanner wouldn’t need to keep state internally, and could always send out the “toggle lock” signal.

Alas, there is no “toggle lock” signal.

Advertisements

Written by Lorin

March 28, 2012 at 5:47 pm

Posted in Uncategorized

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: