Measuring Tire Pressure By Cutting A Hole In An Inner Tube

RFID tags are really very primitive pieces of technology. Yes, they harvest energy from an RFID reader and are able to communicate a few bits of data, but for a long time these tags have been unable to provide useful data beyond a simple ID number. [CaptMcAllister] found a new RFID sensor platform from TI and managed to make a wireless pressure sensor that fits in the inner tube of his bike.

The sensor [Capt] is using comes from TI’s RF430 series that include a few neat sensors that don’t require batteries, but are still able to communicate sensor data to a cell phone or other RFID reader. With a pressure sensor, this tiny microcontroller can receive power from an RFID reader and send it back to a phone app, all without wires.

[CaptMcAllister] cut open an inner tube for his bike, epoxied his PCB to a patch, and sealed everything back up again. After a quick test for leaks, [Capt] found the data coming from the sensor was extraordinarily accurate, and should hold up well enough to be used in his bike.

56 thoughts on “Measuring Tire Pressure By Cutting A Hole In An Inner Tube

  1. it would be more reliable if it was made in the form of a valve cap.
    And maybe a piezo to power a low power bluetooth by centrifugal force /bumps /vibrations, if that is a thing.
    I dont see an inner tube that has been cut to be a good idea to ride into the woods far from home.
    Anyway just an idea.

    1. By the time you get it packaged up in something weathertight and durable you would have something somewhat bulky hanging off the valve stem which might cause damage too. I dont think you need to cut out a chunk of the tube like he did, just make a small incision and slip it inside, maybe a little double sided sticky to hold it in place and then seal it back up. A good patch is as leak tight as a intact inner tube, especially if you are starting with a brand new tube.

      1. This is a cool project, but not terribly useful. You can, by and large, look at a tire while on the bike or riding and tell if it’s too low – most people who have been riding a few weeks/months can tell when their tires are low just by feel…but really, if you ride regularly, you buy a $30-ish floor pump, and you periodically check tire pressure. The higher the tire pressure, the more often you need to check, though there are some really nice tubes out there that don’t leak much at all.

        This introduces a sizable imbalance that’s not great, too. If it’s fixed somewhere on the rim, you can add a counterweight, but not with the present design.

        Also: there’s going to be a sad day when the widget gets smunched by hitting a hard bump or pothole. It’s pretty normal for the tire to get pushed in so far it almost, or does, contact the rim. “Snakebite” punctures are what happen when something pushes into the tire hard enough against the rim, that it causes a puncture.

        I agree that this would be a much more durable design if it could be fixed externally to the wheel. Still, from an electronics perspective, very cool.

        1. Actually this is very useful coming from someone who rides quite regularly. Although this isn’t something a typical rider would be interested, on a competitive level I can easily see how professional riders would want stuff like this. You could easily optimize a bike/rider with data like this.

          1. Well, it’s very cool, but it looks like a solution for no problem.
            When you ride only on a few occasions a year, you will have to refill the tires anyway.
            When you are a frequent / commuter rider, you will feel that your tires start to get soft and refill them when needed.
            And as a professional? You (or someone that is paid by your employer) will check the tires (and everything else) before every single ride.

          2. I can attest the professionals and even competitors have the pressure dialed in for races on road and off road. Those who compete have enough experience riding their bikes to notice differences in pressure just by feel and handling, and even if they haven’t, they generally ride the same tire pressure or know how to adjust based on their own bike’s differences like tire width, rim width, suspension stiffness/rebound/pressure, geometries and their riding style.

        2. You got me thinking, when I check a tire I pinch is with fingers on either side to gauge the pressure, now surely you can do that mechanically and then electronically too, some sort of clamp on the sides and a measuring device to see the resistance.
          You’d have to set a baseline though, normally with nobody on it since people weight fluctuates, not just from food but also from water, evaporation and such so even during a bike ride it changes.

          Anyway, that way you’d need no mechanical changes at all.

      2. You could also lead a tube from the valve to a device of course.

        But actually, I know many cars can measure tire pressure, and they don’t use valve-based sensors I think, which means there must be sensors inside the tire too, which means there might be ready-made RFID thingies available already. Although I’m not sure if they are small enough and adjustable for bicycle tires. Or if you could source them without a tire, although I imagine scraped tires might allow you to retrieve them.

        Just checked and all manufacturers have RFID car tires, one of the reason being this:

        “On Nov. 1, 2000, the U.S. Congress enacted the Transportation Recall Enhancement, Accountability, and Documentation Act, or the TREAD Act, which, among other things, required new motor vehicles from 2004 onwards to have a system that “warns the operator when a tire is significantly underinflated.” “

        1. Have a look round, most TPMS sensors are in the valve or cap, but modern OEM ones tend to be inside the wheel as part of the valve assembly, the rim has a machined space for them to compensate for the imbalance.

      3. You’re right. Most riders I know patch the tube until it falls apart. A good patch doesn’t really leak.

        The hole I cut was definitely overkill – I just did it as a crude prototype to prove the concept. If I were to do this as a product, I would do it on a flexible circuit with Kapton for the components and PET to carry the antenna. Problem is, the minimum order quantity on something like that is about $5k.

    1. I remember about reading about such thing maybe 15-20 years ago. It was a science fiction to me at that time, but some high-class cars had it. Sensor was fixed to the rim so it can sense pressure inside the tire. It had coil for powering the thing and RF transmitter to report tyre pressure to the car. Other coil was on the car and was constantly providing the power. Something like RFID but in much more primitive form. With today’s electronics this can probably made much simpler, without need for external power.

  2. was going to say the same thing

    l wonder about tubeless sealant though
    it’s latex based and uses amonia and propaline- glycol as solvents/caryers

    seems like the amonia would be hard on the sensor
    and the see lantern might coat it and disable the mechanism?

    of course squeezing the tore with my thumb and for finger has always been plenty reliable for me…


    1. I see you are having issues with your auto-correct function there, I think you must have accidentally set it to suggest poetic phrasing.

      I do like sea lantern though. Has a romantic, bitter-sweet image.

  3. I must be missing something about the construction details. For such a pressure sensor to work wouldn’t one side have to be expose to the interior of the tube, the other exposed to the atmosphere? I’m not seeing how this is accomplished without exposing the sensor and electronics to road shock. I’m sorry in general I find the projects hosted at hackday .io have far less detail than projects hosted elsewhere. Project hosted at instructables are often better in detail, if I permitted to commit such a sacrilege. Because poor people have to depend on poor ways, I have made question repairs in inner tubes. So I have an idea what was done here put the details don’t really confirm it, so I’m unsure if those not experienced with inner tube hacks out of necessity can duplicate this if they wanted to.

      1. An android barometer mechanism did come to mind when I was trying to sort this through, but I didn’t dwell on it long enough I suppose. This hackday post. the io project page, or the TI link didn’t have an easy path to the actual sensor used, thanks for the input.

          1. Hi — Excellent post. My only comment is that given an aneroid, and no outside reference, you are measuring absolute pressure. By calibrating this to a known reference (using a standard air pressure gauge referenced outside through the valve stem that does reference pressure to barometric pressure) you are using PSIg as a reference point for your PSIa. This is fine, however without a constant reference to barometric pressure, your readings are never PSIg (gauge pressure) but no doubt never far off from it, unless you bicycle up 8k ft. after calibrating to sea level :)

  4. Ya know, I tried this same thing a while back, but I was too worried about the patch leaking, so I just filled the tube with high density urethane foam instead. No leaks now, and the sensor has a nice, cushy home.

  5. Uh, ok, I get it, it works remotely, you do not have to check pressure, etc. But why cant he just insert the sensor into the tire and leave the board outside? Well, ok, it has been mentioned already.

    But why on Earth did he cut a whole piece of tube out? You can just make a lengthwise cut, push the sensor through the hole, glue it inside and cover the hole with a patch! Or even vulkanize it, it will be stronger.

    No, he cuts a whole piece out and covers it with a patch. The seam is more likely to fail and the patch will bulge out it seems.

    1. To be fair it is still trivial to fix, and will probably never result in any problems anyways. Patching bicycle tires in the field is one of the most error tolerant procedures I ever do.

  6. Nice sensor but not for a bike tube.
    The Electronic part is too big for this project.
    When riding the big the space inside the tube is too small.

    Try again with a bigger tire like car, truck, or something like that.
    When using a tubeless you could glue the sensor to the inside of the rims.

    But again nice sensor

  7. Or, you could just have a sensor between the tube and rim pushing against the outside of the tube measuring the force, making tubechanges a lot cheaper and faster.

    But as said before, pressure sensing valvcaps is already out there

    1. Not that it makes any sense to monitor a bicycle’s pressure pre / during / post biking – other than using your thumbs (when parked) or your eyes (while riding). But I too would put a sensor between rim and tube to make it easy.

  8. I always love the condescending” but this is already out there” responses.

    Is it the best design? No.
    Is it the best usage? No.
    Is there already an answer to the problem? Yes.
    Does any of this mean that he shouldn’t try to do this and work on improving his idea? NO!

    Many current inventions/ideas/products are just rehashes of old concepts. If we all followed the “its already been done, why do it again?” line of thinking, we would all drive Fords that were black, watch the roads by way of light given off by Edison bulbs, and likely still be watching Sony Tritron TV’s.

    If imitation is the sincerest form of flattery, it is also the best form of competition An idea that sits in only one set of hands is doomed to stagnate..

    1. Yeah, I was actually thinking of trying to do something with some sort of sales, but I’m not sure where to start. I think it would work better for casual riders who aren’t on 700×23 tubes like I am – riders who don’t check their tire pressure often and may not have a floor pump with gauge. I also thought it would be even better for footballs (inflategate) or basketballs since I doubt they have as much stress on them.

      If it were marketed, I would make the whole patch flexible – no rigid PCB. I think it could be made much more durable and would have only a small incision in the tube for just the pressure sensor. I’ve got a design that could be made in PET, but the minimum order for such a design is like $5k.

  9. It’s nice to see someone’s had a go on their own and succeeded, but I’m wondering if anyone’s taken apart an automotive radio valve yet. Though auto manufacturers are starting to move away from those and starting to calculate tyre pressure from rolling diameter by using ABS and wheel speed, so I’m sure that could be done too.

      1. I went through a machine at a motorway services a couple of months back. I drove through a 8metre long section and it read the pressures in my tyres quite accurately. When compared up against a hand gauge they were 1-2 psi out on all four readings. I’m going to assume it was a weigh bridge as well as measuring the contact patch of the tyre. Similar technology to the rollerless brake testers.
        Doing this constantly with the ABS sensors and knowing the tyre size fitted and both static and dynamic loads (shock travel monitors) would seem accurate way to do it also.

  10. The downside is that bicycle tyres squash easily, hit a pot hole or some other sort of bump and the sensor will get crushed. Would probably work a lot better in a car with tubeless tyres as the wheel could include a metal shroud for the sensor to sit in. That way if you mount a kerb or something with a low tyre pressure the sensor won’t get smashed.

    1. I wonder how heavy a circuit would be if you protected it enough to handle the wight of a bike+person.
      I have a feeling it can’t be that hard to do. I mean I think I might be able to stand on some commercially available USB sticks and have them survive for instance, if something is small and simple and has no display and other such weak points it should be doable

  11. Car pressure sensors are actually attached to the valve, mounted on the inside of the rim and use coin cells for power.
    It is probably a better way to fixate the sensor inside of the wheel, instead of just putting the bare pcb inside or glueing it to the tube.

    1. while the sensors are *only* $70 the required receiver/gps is another $600… seeing as that is more than most “casual” riders spend or their entire bike that really doesn’t seem like a logical idea.

      1. That thing is for a motorcycle though. But yeah too pricey even for that.

        I mean you can put a $1 pressure gauge on the valve when it’s parked, so the only time you need a complex life thing is when you suddenly lose pressure while on the road but for some reason don’t notice.

        Cars are different I think because few would walk all around the car on a regular basis to check pressure, on a motorbike that action seems much easier. Plus you’d sooner see it on a bike if there’s a noticeable loss of pressure when you approach it, since you can eye all wheels in a glance.

        And talking of noticing, I can certainly feel it when a bicycle loses pressure, you feel every bump you pass over, and the force to keep going becomes noticeably larger and in corners you also feel the difference.

  12. My car moniters tire pressure by counting wheel rotations for each wheel. Then based on average rotations and some algorithm it can figure out when a tire is low because its rotation is different from the others.

    It’s an alternate method some car makers use instead of active valve stem tpm systems that cost a lot more.

  13. Put it in the valve stem of a tubeless setup and encapsulate it to keep the sealant out. Ideally is woul narrow enough to tuck in the rim so doesn’t get crushed on rocks. A solid idea technically, but not sure how practically useful it would be, but then I would have said the Sam tthing several years ago about wireless battery powered deraiullers. Tubless systems are mostly on MTBs but are finding their way into road bikes, but as some have already said, most people who bike seriously check their tires often (before rides) and only loose significant pressure due to blowouts. Maybe commuter d city bikes that don’t get used as often could use it like car TPMS to alert riders.

  14. This is the dumbest waste of time. Want to know if your tubes need air? Get on top of your bike. What happens if you run over a nail or a thorn and crush the chip as your tire deflates? You’re out $11 plus the cost of a new tube.

  15. On to the advancements in RFID, the hobbyist market still seems to be constrained to HF RFID tags, typically those using inductively coupled antennas.

    The state of art in RFID has moved to UHF, for FCC, that ISM 902 – 928.

    Check out IC’s like EM marlin EM4325 – this chip has its own temperature sensor, and SPI interface to a microncontoler or other thing – it can harvest energy and reply or it can work by using assistance from a battery.

    companies such as Farsense (in spain) and others have innovated pretty nifty devices based around MAXIUM passive power electronics SOICs to harvest waves, boot up a nanowatt MCU, and send back acclrom, pressure and other data in the UHF range – meaning long distance communication.

    I hope some day we can have a cheap, affordable open UHF rfid reader so the hobby space can start to use and understand these cool devices.

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