How does (very sensitive) passenger seat seat belt sensor work?

[FRSBRZGT86FAN]

Originally Posted by Dake

A certain amount of weight does activate it as well though. My beagle is 35 lbs and if he sits just right in the seat, he'll trigger the warning. I think it triggers for less though, I'm pretty sure I had a couple gallons of milk there and that was also enough.

The condensation on the milk would be enough to trigger it honestly....

[FRSBRZGT86FAN]

Originally Posted by Tcoat

The Carista app can also turn the chime off as well as many other things. Don't know how the cost compares to a legit Techstream but there may be a savings to be had.


https://caristaapp.com/vehicles/scion/fr-s/1st-gen

Well tech stream you have you buy a usb to OBD2 cable off ebay from $14-$20, and you just pirate the software

Carista has changed their policies around so much I think it's $20+ for all modification unlocked permanently and $20 for their adapter which works better than the other elm327 dongles I've had. And it works on multiple cars other than toyota.

Regardless they are both well worth it.

[venturaII]

I can confirm that three spaghetti squash were enough to trigger the alarm. lol

[ermax]

You can get a Techstream compatible cable on Amazon for $18. Everyone should have Techstream in their tool box.

[Ultramaroon]

Originally Posted by Dake

A certain amount of weight does activate it as well though. My beagle is 35 lbs and if he sits just right in the seat, he'll trigger the warning. I think it triggers for less though, I'm pretty sure I had a couple gallons of milk there and that was also enough.

water/flesh


A wet towel will trigger it.

[Tcoat]

Originally Posted by Dake

A certain amount of weight does activate it as well though. My beagle is 35 lbs and if he sits just right in the seat, he'll trigger the warning. I think it triggers for less though, I'm pretty sure I had a couple gallons of milk there and that was also enough.

There is no mechanical weight trigger. Your dog and milk contain liquids and that is what it is sensing. You could pile dry bricks up there all day long and nothing would happen. Soak the bricks first and bingo.

[Dake]

Originally Posted by Tcoat

There is no mechanical weight trigger. Your dog and milk contain liquids and that is what it is sensing. You could pile dry bricks up there all day long and nothing would happen. Soak the bricks first and bingo.

This isn't completely right though. Here's a metal dumbbell in my pax seat. It is not damp, nor is the seat, but you can (fuzzily) see the light is illuminated to say the seat is occupied and the airbag is on.



The picture you showed is a capacitive pressure sensor. If enough of the pad is depressed, it reduces the resistance to a point to trigger the system as thinking someone is in the seat. Here's a simple description of how it works.

Just thinking logically, a "moisture sensor" would be a pretty strange way to measure occupancy. If you get dressed in the morning and put on a fresh pair of clean jeans and walk out the door, there is not enough time for your body's "natural moisture" to seep through the jeans and through the seat fabric. Are you suggesting the car won't think someone's in the seat for however long this transfer takes place?

I'm not saying moisture doesn't interfere with the system in some way and cause a false signal (probably by also reducing resistance). Similarly our cell phone's signals interfere as well.

But primarily it relies on a certain pre-programmed amount of weight. This is intentional because it was learned long ago that an airbag deployment with a small person can do more harm than good. Remember when we had manual buttons, switches, or even a key hole to turn off the airbag if a child was in the front seat? That child would still generate "moisture" today, yet the airbag does not turn on if it doesn't meet the threshold.

[ermax]

This sensor very literally does NOT measure weight (in the physical sense). Period. That dumbbell is made out of medal which is conductive therefore you can induce it with electricity and then measure the capacitance of it. The sensor however was designed and tuned to measure the mass of a human body based on it's capacitance. Anything else placed on the seat will not be accurately measured. For example a cell phone, charging cable, wet towel, ect ect. Actually even an underweight child with wet pants on will cause it to think it's an adult because the water causes the electricity to conduct better throwing off the calculation. If you spill a drink on the seat it will think someone is sitting in the seat too.

This is also explained in the owner's manual BTW.

Also, the sensor you linked to is NOT what is used on our car. What you linked to was the older style with two layers which short together when a specific weight is applied to it. We have a capacitive system in our car. It's purely electric. Think of the two styles similar to how you would think about a resistive touch screen vs a capacitive touch screen. A resistive touch screen uses two layers of film that short together when being pressed. They work great in industrial applications where people have on dry gloves. Then you have capacitive touch screens which can't be used with gloves on (unless you have special conductive gloves).

I believe they went with a capacitive system because they are more durable. The old resistive types become inaccurate after weight and heat has been applied to them for years. The layers lose their rigidity and collapse too easily.

[Dake]

Ah gotcha. So it's more about conductivity than "moisture".

Knowing is half the battle.

[Tcoat]

Originally Posted by ermax

This sensor very literally does NOT measure weight (in the physical sense). Period. That dumbbell is made out of medal which is conductive therefore you can induce it with electricity and then measure the capacitance of it. The sensor however was designed and tuned to measure the mass of a human body based on it's capacitance. Anything else placed on the seat will not be accurately measured. For example a cell phone, charging cable, wet towel, ect ect. Actually even an underweight child with wet pants on will cause it to think it's an adult because the water causes the electricity to conduct better throwing off the calculation. If you spill a drink on the seat it will think someone is sitting in the seat too.

This is also explained in the owner's manual BTW.

Also, the sensor you linked to is NOT what is used on our car. What you linked to was the older style with two layers which short together when a specific weight is applied to it. We have a capacitive system in our car. It's purely electric. Think of the two styles similar to how you would think about a resistive touch screen vs a capacitive touch screen. A resistive touch screen uses two layers of film that short together when being pressed. They work great in industrial applications where people have on dry gloves. Then you have capacitive touch screens which can't be used with gloves on (unless you have special conductive gloves).

I believe they went with a capacitive system because they are more durable. The old resistive types become inaccurate after weight and heat has been applied to them for years. The layers lose their rigidity and collapse too easily.

This ^ All of this.

Originally Posted by Dake

Ah gotcha. So it's more about conductivity than "moisture".

Knowing is half the battle.

That was why I picked dry or wet bricks not metal dumbbells for the example.