Tire Pressure Monitor Sensor (TPMS)

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,069
Replaced some failed TPMS on my truck. Have the old ones and have peeled them open. Found a very large Swiss made coin battery which is too weak to run the sensor. There's also a transmitter circuit and coiled antenna, but the thing I'd like to know more about (wondering if I might use it in a project) is the actual pressure sensor transducer chip.

It's a GE made product and the numbers on it are
C01768
1237052

I've not had any luck on Google or Yahoo. Found something of a sort of transducer on Amazon, but they're all completed units, not the actual chip itself. No serious projects planned, just wondering exactly how I'd use it. Any help would be appreciated. Like I said, this is not a serious project, just something that if I know how it works I might find a use for it.
 

Reloadron

Joined Jan 15, 2015
5,995
MMmmm. I guess nobody has any input.
I am also curious about those things. I have an intermittent one on my truck. Also at some point before I owned this truck the order got screwed up as RF, LF, RR. and LR are not where they should be. I know the problem so no big deal but I would be curious exactly where in that tiny board the actual sensor is? See any small chips with a small hole in them? :)

Ron
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,069
The chip has 14 pins (SMD). The only other chip on board has 8 pins and is labeled T579 / 219.

There's a crystal oscillator (don't know if it's crystal or other) with a frequency of 9.84375.

There doesn't appear to be a micro on the board but there's this really really long coil, estimating about 2 mm wide by about 15 mm long. Biggest coil I've ever seen like it. I'll take pictures of the board another time, but tracing the circuit is going to be very difficult because a lot of the board was covered with some soft spongy potting. Definitely two layer, possibly more. I'd doubt it because the circuit doesn't appear to be that complex. Basically the oscillator and the sensor along with a very big coin battery and a short 3/4 inch looped antenna of 3 turns.

Just wondering if it's worth going after the pressure sensor chip.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,069
at some point before I owned this truck the order got screwed up as RF, LF, RR. and LR are not where they should be.
I don't think it matters on my truck where which sensor is located. Every oil change I have the tires rotated and never get a light.

Probably a universal location for those sensors is on the valve stem. That's where mine are and that's probably where they are on all vehicles.

Yes, there's a chip with a tiny hole in it. It's the chip I listed in post #1.

When tearing one apart start by sanding off the edges. The cover will likely be somewhat glued down with some kind of potting. The stuff on mine is easily cut through with a knife. Just don't spill any blood. Easy to slip and slice. I'm told that they last about 5 years. The batteries are not replaceable. Not without cutting the whole thing open and then having the ability to weld flat wires onto the battery. Just one coin battery. Tomorrow I'll get around to taking pictures of it and post what's going on. In eluding that very oddly large inductor.
 

Reloadron

Joined Jan 15, 2015
5,995
Thanks for sharing that Tony. Maybe this spring I'll replace mine. They say battery life on newer ones is over 5 years. My best guess is the chip with the hole is the sensor, at least that would seem logical to me. :)

Ron
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,069
My best guess is the chip with the hole is the sensor
Definitely the sensor. It had a rubber gasket between the chip and the exterior of the sensor assembly. The tiny hole went through the case, the gasket and into the chip. So I'm sure that's the PT.

Certainly was interesting opening one up.
 

bwilliams60

Joined Nov 18, 2012
1,407
Tire monitor sensors can be direct or indirect type. Indirect type does not have a physical sensor but measures wheel rotational speed. If a tire is low on air, it will spin faster because of the smaller diameter. A direct type sensor is usually mounted on the valve stem and sends a signal to a control unit which manages the system on the CAN BUS. The sensor can also be strapped to the rim inside by a clamp. When changing tires, if not done properly, they are usually damaged. The sensor itself I believe is some form of piezo but I have not been able to prove it. They also have a centrifugal switch which "wakes" up the system when it starts to move. A loss of 2 psi usually is enough to set a code. The sensors are all "found" by the monitor when it is awake and knows where all of the signals are coming from. They generally do not have to be programmed although some of the higher end vehicle may require it. Most monitors will find the sensors with a simple road test. Hope this helps.
 

Reloadron

Joined Jan 15, 2015
5,995
That's good to know. I can scroll through mine and read individual pressures. The common error I see is when it tells me Check Tire Monitor and as I scroll through my one intermittent sensor will display ---- rather than the usual PSI reading. When a tire gets low I get a light on the dash reflecting a low tire pressure as well as a warning when I scroll to that tire. The truck is an older 2007 GMC Yukon Denali.

Ron
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,069
Programming: When I changed the TPMS (not me personally) my truck (2008 Toyota Tacoma - my "Taco") the truck's computer had to be uploaded with the new sensors. All five of them. Yes, even my spare tire has a TPMS. I can't just simply change the sensor. I'll get a code if I do. The sensors have to be read by a reader and then the reader is plugged into the OBDII port and the technician does something. I think he pushes a button under the dash and the computer will learn the new sensors. But like I said earlier on, it doesn't matter where each sensor is located. As long as the computer knows what five sensors its looking for it will find them on any corner of the car or under the truck bed (spare).

Have to run out for a short while but I'll come back and take some pictures of the pealed sensor and post them.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,069
How long are they expect to last
The guy at the tire shop said they last 5 to 7 years. The spare tire is factory original and still going strong. I guess since it's not on the road it's not transmitting. Not unless the PCU is searching for a signal periodically. So the spare is 10+ years. The ones on the four corners lasted about 5 years. That's when I put the rims on my taco.

One coin cell?
Yes. But it's a lot bigger than a regular coin cell. The Swiss Made cell is a CR2450.
 

BobaMosfet

Joined Jul 1, 2009
1,821
The chip you're talking about is this chip, made by Amphenol: NPX-C01768

And thanks... I've been wanting to find one of these for a number of uses ;)
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
6,069
I've been wanting to find one of these for a number of uses
Would you be willing to share your "uses"? I have a few of these and don't know what to do with them. Don't know that I will ever do anything with them, but maybe if you were to say "I want to use one of these to measure the thrust gas pressure on my space ship", maybe I'll build one too.

One thought came to my mind: Use one of these sensors on the nose of my Taco to measure wind resistance. To see how wind changes gas mileage. I know driving into a head wind uses more gas; just wondering how much more pressure is on the nose. Drove from Utah to Wisconsin a couple years back. Going there I got pretty good gas mileage. Coming home I was fighting a headwind all the way and it sucked down the gasoline.

Of course I don't know what I'd do with that information, but aircraft use a Pitot tube facing into the wind as they fly. The air pressure is translated into an air speed. Would be interesting to see how close to a big rig tractor trailer I'd have to get to significantly lower the pressure on the nose of my Taco.
 
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