4 ms·

I had a '94 Corvette that did this. Probably to save on battery life. There was a tiny ball that moved around in the key fob. The fob wouldn't transmit the "hey

I had a '94 Corvette that did this. Probably to save on battery life. There was a tiny ball that moved around in the key fob. The fob wouldn't transmit the "hey, I'm here" signal unless it was moving. Not sure what the tech was. Not an accelerometer per se, but still motion detection that worked pretty well.

abraae 9y ago
Perhaps a strain gauge (https://en.wikipedia.org/wiki/Strain_gauge https://en.wikipedia.org/wiki/Strain_gauge), a primitive sort of accelerometer that has been around for donkey's years.
- consp 9y ago
  If it is a ball it probably is a ground plate on the bottom and top with sense connector plates on the edge of the box where the ball is in. The ball moves around and if it gets a connection (ground to sense) a counter gets increased and a time gets reset and since you are moving the thing usually moves around and make some connection when braking/accelerating/steering. You need bumpy roads though on longer trips on the highway. Dirt cheap, but unreliable. Straingauges (in my experience) generally need to be tuned for every gauge which makes them somewhat more expensive.
  - function_seven 9y ago
    Oh, I think I misread my parent's comment. On my fob, it was purely to unlock the doors when you approached the car. It didn't involve itself with the ignition or running of the car. That was still an old-school key (but with the tiny improvement of a known resistor ohm-age in the key itself†) † http://ricksfreeautorepairadvice.com/gm-anti-theft-systems-overview/ http://ricksfreeautorepairadvice.com/gm-anti-theft-systems-o...
- function_seven 9y ago
  One of those may have been involved somehow, but there was definitely a rattling ball in there you could hear if you shook it. I'm having trouble finding images of how it worked, but many car forums discuss the "small gold bearing in a cylinder" that's used in the fob. Unfortunately, Google wants to show me links to buy stuff. It's getting impossible to find "standalone" web pages these days.
GoToRO 9y ago
Tiny ball of mercury that moved inside a glass bubble. The glass has tiny contacts on the inside and the mercury would short circuit at least two at a time. It would detect sudden moves. This is one type of tech that worked like that but maybe not exactlly like yours.
- function_seven 9y ago
  Probably similar to your description, but it was a solid ball that rattled. The enclosure was metal as well I think, though maybe some sort of laminated shell with alternating contacts? I'm really trying to find a diagram of it, but my searches aren't yielding much.
  - K0balt 9y ago
    Ball motion detectors (or shake/tilt switches) work as you describe. They typically have several metal rods on which the ball will rest on two at any given time. The impossible combinations (too far away to span with the ball) are often bridged together for simplicity. Detection is done by monitoring for changes in the connectivity between 3 or more contacts.

abraae 9y ago

Perhaps a strain gauge (https://en.wikipedia.org/wiki/Strain_gauge https://en.wikipedia.org/wiki/Strain_gauge), a primitive sort of accelerometer that has been around for donkey's years.

consp 9y ago
If it is a ball it probably is a ground plate on the bottom and top with sense connector plates on the edge of the box where the ball is in. The ball moves around and if it gets a connection (ground to sense) a counter gets increased and a time gets reset and since you are moving the thing usually moves around and make some connection when braking/accelerating/steering. You need bumpy roads though on longer trips on the highway. Dirt cheap, but unreliable. Straingauges (in my experience) generally need to be tuned for every gauge which makes them somewhat more expensive.
- function_seven 9y ago
  Oh, I think I misread my parent's comment. On my fob, it was purely to unlock the doors when you approached the car. It didn't involve itself with the ignition or running of the car. That was still an old-school key (but with the tiny improvement of a known resistor ohm-age in the key itself†) † http://ricksfreeautorepairadvice.com/gm-anti-theft-systems-overview/ http://ricksfreeautorepairadvice.com/gm-anti-theft-systems-o...
function_seven 9y ago
One of those may have been involved somehow, but there was definitely a rattling ball in there you could hear if you shook it. I'm having trouble finding images of how it worked, but many car forums discuss the "small gold bearing in a cylinder" that's used in the fob. Unfortunately, Google wants to show me links to buy stuff. It's getting impossible to find "standalone" web pages these days.

GoToRO 9y ago

Tiny ball of mercury that moved inside a glass bubble. The glass has tiny contacts on the inside and the mercury would short circuit at least two at a time. It would detect sudden moves. This is one type of tech that worked like that but maybe not exactlly like yours.

function_seven 9y ago
Probably similar to your description, but it was a solid ball that rattled. The enclosure was metal as well I think, though maybe some sort of laminated shell with alternating contacts? I'm really trying to find a diagram of it, but my searches aren't yielding much.
- K0balt 9y ago
  Ball motion detectors (or shake/tilt switches) work as you describe. They typically have several metal rods on which the ball will rest on two at any given time. The impossible combinations (too far away to span with the ball) are often bridged together for simplicity. Detection is done by monitoring for changes in the connectivity between 3 or more contacts.