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Old 03-25-2018, 03:34 PM   #1
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Fun with TPMS - what engineers do when they are bored

Since I'm pretty much done with this guy: DIY Capacitive tank sensor

I figured: Hmm what other thing can I make overly complicated and write some software for? Oh look I can get Bluetooth TPMS sensors. I wonder if I can reverse engineer those??

Turns out: Yes you can.

I picked up a set of these guys (6 to start with): BLU Technology Products | Home (external sensors), grabbed my spare tire for the dolly (smallest tire I can bring indoors) and did a little hacking

Turns out the sensors are Beacons and broadcast the pressure and temp on a regular interval (somewhere in the range of 10-15 seconds--at least when the tire/wheel is sitting on the floor in my office).

The conversion from raw data to PSI is pretty straightforward (have to figure out the temp one..don't have enough values there like I do for pressure--I filled the tire up to 80+ PSI and took readings as I lowered the pressure in the tire, made a handy graph in excel..hey look its linear! LOL).

Why do this? Well instead of just running their app in which you set valid ranges and it alarms you when the tires go out of that range I figured I'll make my app log the temp/pressure over time (and probably graph it). May notice something a lot earlier than simple alarms.. who knows.

More data is better right..?
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Old 03-25-2018, 03:38 PM   #2
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Cabin fever?

Suppose to be spring here. I just shoveled the foot of snow off the RV roof.
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Old 03-25-2018, 05:46 PM   #3
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Jamie, You sound like the IT guys that used to work for me. After he got done explaining the "system" to me I would have him explain it again "in english please" and in one sentence.

I think it's time to go camping!
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Old 03-25-2018, 05:49 PM   #4
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Quote:
Originally Posted by JamieGeek View Post

.....cut....

More data is better right..?
In general I take the simpler straight forward approach ó drive if you have enough pressure, stop if you donít.
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Old 03-25-2018, 06:19 PM   #5
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Wow!

This ranks up there with the fellow I know, that figured out how to make the fuel gauge on his Spyder read VERRRRY precise!
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Old 03-25-2018, 06:58 PM   #6
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In general I take the simpler straight forward approach ó drive if you have enough pressure, stop if you donít.
Ah but if something appears strange and is an indicator that you won't have enough pressure soon you are better off with that warning than all of the sudden you don't have any pressure... Granted any TPMS will give you that to some degree: Right rear outside tire running warmer than the rest, Right front pressure dropping, etc.

Quote:
Originally Posted by Miramar Owner
Jamie, You sound like the IT guys that used to work for me. After he got done explaining the "system" to me I would have him explain it again "in english please" and in one sentence.

I think it's time to go camping!
LOL I left out quite a bit of the details above.

I'm more than chomping at the bit to go camping, but sadly the wx here has been messing with us: 20s overnight and a very sunny and bright 40s during the day--taunting us since we can't dewinterize just yet...

Just happy we didn't get the blast of snow that blanketed a little west of us late last week, or any of the 4 nor-easters that hit the east coast lately..more taunting: no snow on the ground here in MI.

Running another experiment: Have the sensor and battery in the refer here in the house. After its good and cold I'll put the battery in and record the readings and the temp it shows as it warms up to room temp--that should get me the equation to convert raw value to degrees F.
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Old 03-25-2018, 07:17 PM   #7
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Good luck!
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Old 03-25-2018, 10:05 PM   #8
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Well the refer experiment worked quite well. I was impatient and the sensor only got down to 41F. Putting it in the sun got a range of 41F - 90F a good range to determine the scaling values.

Pretty pictures:

PSI scaling, input sensor reading is the X axis, output PSI value is Y (vertical).
Click image for larger version

Name:	PSIGraph.PNG
Views:	108
Size:	24.7 KB
ID:	9466

Temp scaling, input sensor reading is X again, output is Y (Orange line is Celsius, blue is Fahrenheit). Extra credit: Guess where the two lines cross (the temperature)?
Click image for larger version

Name:	TempGraph.PNG
Views:	145
Size:	21.9 KB
ID:	9467

(If you are curious of how I got the data--e.g. how did I know the temp--I used the "official" app. Since the sensors are Bluetooth Beacons: Bluetooth Beacons broadcast their data. Thus you can have a phone running the official app displaying the data converted to something readable, and some other device also displaying the raw values.)
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Old 03-25-2018, 10:11 PM   #9
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(Pretend you're talking with someone who has NO idea what you're talking about... )

Is there a practical use for this knowledge; or is it best to just purchase a tire pressure and temperature monitoring system?

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Old 03-25-2018, 10:20 PM   #10
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(Pretend you're talking with someone who has NO idea what you're talking about... )

Is there a practical use for this knowledge; or is it best to just purchase a tire pressure and temperature monitoring system?

LOL! Yeah just pick up a TPMS and don't worry about this.

I'm basically reverse engineering the hardware so I can write my own software for the TPMS. The sensors don't output numbers in the units you want (it'd be great if the pressure sensor just spit out a PSI value every few seconds, but it doesn't do that). Instead, what they did is use the range of available values and scale it to that range.

Lets say you had a system that let you transmit only the number values from 0 to 200 (for whatever reason). You want to make best use of what is available so you scale your sensor output to that range (say you have a voltage sensor that outputs 0-20V). Then you'll want to transmit a value that takes advantage of the available values so you transmit the sensor value multiplied by 10 (then the receiver divides by 10 and displays xx.x values).

My graphs above are my attempts at determining what the conversion is from the raw data transmitted by the sensors to a human readable value (PSI, degrees F, etc.).

Like I said: What engineers do when they are bored... LOL math problems
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Old 03-25-2018, 10:50 PM   #11
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Now I DO understand Math problems :
"99 bottles of beer on the wall..."
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Old 03-26-2018, 01:56 AM   #12
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......cut.....

Temp scaling, input sensor reading is X again, output is Y (Orange line is Celsius, blue is Fahrenheit). Extra credit: Guess where the two lines cross (the temperature)?
Attachment 9467

......cut.....
-40 seems like the logical guess.

And it looks fairly close.
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Old 03-26-2018, 11:26 AM   #13
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-40 seems like the logical guess.

And it looks fairly close.
LOL Yep -40 it is.
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Old 03-31-2018, 05:09 PM   #14
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Originally Posted by JamieGeek View Post
Since I'm pretty much done with this guy: DIY Capacitive tank sensor

I figured: Hmm what other thing can I make overly complicated and write some software for? Oh look I can get Bluetooth TPMS sensors. I wonder if I can reverse engineer those??
Nice to see another "gearhead"on here. You might find these little Bluetooth devices fun to play with. https://www.bluemaestro.com/

They are various sensors (Temp, Temp & Humidy, Pressure, Movement & Shock) and data logging devices, using Bluetooh beacon technology. I got a couple of the temperature discs to monitor and log the cold temperatures in the wet bay during these cold nights. The accompanying app is well done and lots of settings, and alarms you can set on the sensors.
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Old 03-31-2018, 08:30 PM   #15
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Nice to see another "gearhead"on here. You might find these little Bluetooth devices fun to play with. https://www.bluemaestro.com/

They are various sensors (Temp, Temp & Humidy, Pressure, Movement & Shock) and data logging devices, using Bluetooh beacon technology. I got a couple of the temperature discs to monitor and log the cold temperatures in the wet bay during these cold nights. The accompanying app is well done and lots of settings, and alarms you can set on the sensors.
I saw those when I was looking around for a BT TPMS. They look really cool. All I need, more DIY projects LOL
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Old 03-31-2018, 09:29 PM   #16
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I just picked up a FOBO setup for my Spyder... It links to the info screen on the bike via my smartphone.
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Old 04-01-2018, 01:58 PM   #17
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Jamie- Hopefully the snow there will melt soon.

Actually it's always fun to see how stuff works..
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Old 04-01-2018, 02:56 PM   #18
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No snow in MI at the moment--at least where we are--just waiting for the overnight lows to be consistently above freezing. Looks to a week or more out for that...
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Old 04-01-2018, 04:03 PM   #19
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We've also been watching those weather reports...

With our fingers crossed!!
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Old 04-02-2018, 02:58 PM   #20
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I am definitely interested in this as well. One thing I do wish I had the ability to do was graph my temperatures over time to analyze the trend data. While driving I spot check my and notice that the PSI tends to increase on the the inside dually tires faster than the outside. If that is the case, I can slightly reduce the pressure on those inside tires to maintain a consistent PSI across the rear axle.

For me, at this point I have invested in the EEZTire system, I think that is just using RF but would definitely jump ship and pick up blue tooth if the ability to track data were to gain some traction in your project.

I'm a long time IT geek and analyst, your work definitely piques my interest
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