Inside the tiny RFID chip that runs San Francisco's “Bay to Breakers” race | Hacker News Reader

Inside the tiny RFID chip that runs San Francisco's “Bay to Breakers” race

righto.com

71 pointsdwaxe23 comments

I use a system like this for tracking drivers and cars in an automotive racing series. I built a system that's hooked up to twilio to send the team a text message with their official pit stop timing.

Sounds like there could be interest in a writeup on this

Um yeah nick... stop holding out on us. ;)

I would be interested in hearing more. I know the FIA/ACO uses RFID to track how many tires are used by each car in the World Endurance Championship and the 24 hours of Le Mans.

Not that it's specific to Bay-to-Breakers. Just about any race I run these days uses some form of chip. I prefer the type in this post because the chip, along with the race number, are disposable and I just have to pin the number on like I would normally. The older tech was a tag that zip-tied to your shoe, and had to be turned back in at the end. Not a huge deal, but attaching a tag to my shoe so that it doesn't flop around, and doesn't cause a numb spot on my foot, is just one more thing to do pre-race.

Yeah I remember those. D-tags I think is what they were called (since they are suppose to form a D on your shoe I guess). The ones on the bibs are way better.

Either way, super interesting technology that I've really haven't appreciated until this post!

It's amazing technology, sucking energy from the air to power analog and digital circuits. Does anyone have any idea how many watts it needs to operate.

Impinj say the tag can perform reads with RF power levels down to -19.9 dBm and writes down to -14.1 dBm.

-19.9 dBm is about 10 uW (micro watts). -14.1 dBm is about 38 uW.

>sucking energy from the air to power analog and digital circuits.

when the AI that writes programs goes wrong, the machine learning will seek out ways to keep circuts on perpetually.

Then, the battle for energy will no longer be scifi.

How do they deal with many chips crossing the line at the same time?

How do they define the line in the first place? The transmitter has to be extremely directional and relatively high power.

There's an anti-collision system which is used to inventory all tags in the field of view of a reader. On the order of 500+ tags per second can be picked up by a single reader. For more details, see the GS1 spec, page 49 or so http://www.gs1.org/sites/default/files/docs/epc/uhfc1g2_1_2_...

> How do they deal with many chips crossing the line at the same time?

The EPC Gen 2 spec has a few ways of avoiding collisions. One is Random-slotted collision arbitration, where a tag waits a random amount of time before responding. There's also a somewhat complex algorithm; basically the interrogator says "I heard from tag X, so X be quiet, anyone else?" and repeats until everyone has been inventoried. The interrogator can also ask for subgroups of tags at a time, "Anyone whose number starts with 1? 2? ..." See [1] for details. The tags are designed to work for inventorying when many, many tags are visible at once. I'm not sure which methods are in use during races; taking inventory doesn't have as much time pressure, of course.

The tags are fairly omnidirectional, but the detection mats are directional. I read somewhere that the timing system has about 300ms accuracy, but I can't find that now. I assume that for the race winners they use highly accurate finish line technology, rather than RFID. (It would also be very embarrassing if the winner's tag didn't scan: "Sorry, we didn't catch your time.")

[1] http://www.gs1.org/sites/default/files/docs/epc/uhfc1g2_2_0_...

There's been talk that RFID could be use to track and pay for groceries in record time. For context, what would the cost be for a chip like this and the additional antenna?

A few cents. Still much more expensive than printing a barcode on the side of an item but can pay for itself through better inventory tracking.

See WalMart's use of RFID for some examples of how RFID is already used in the way you ask about. http://www.rfidjournal.com/articles/view?7753

Unfortunately to achieve the 'holy grail' of being able to scan every item in a customer's basket would need a one cent tag on a thirty cent can of beans - which just doesn't sound economically feasible.

And that's assuming you can get a tag that will read reliably when stuck to the opposite side of a metal can for that price.

Parent's "a few cents" and what I pay in SoCal for a can of beans ($1.40 regular price; $0.99 on sale) indicate a different scope.

You project a 1:3 ratio. Cheaper estimates of chip cost, more expensive beans suggest the other end of that ratio is $0.03:1.40 indicate the chip cost around 2%, which could potentially be recouped by better inventory practices.

I don't dispute you can spend $1.40 on a can of beans if you're buying premium brand, but in Asda (a British supermarket chain brought by Wal-Mart a few years ago) I can buy a can of "SmartPrice Baked Beans in Tomato Sauce" [1] for £0.24 (about 33 cents) and a can of "SmartPrice Mushy Peas" [2] for £0.16 (about 22 cents), and a can of "SmartPrice New Potatoes in Water" [3] for £0.15 (about 21 cents).

If you can get those goods onto shelves profitably and spare a cent for an RFID tag, you could have a successful career in grocery retailing :)

[1] https://groceries.asda.com/product/baked-beans/asda-smartpri... [2] https://groceries.asda.com/product/peas/mushy-peas/34117 [3] https://groceries.asda.com/product/potatoes-instant-mash/asd...

I remember a Walmart IT manager spoke to my IT Senior Seminar class in 08, and said that they were RFID to the pallet level and were working to go down to the carton/case level. I have no idea where they are at now.

Reliable UHF RFID when tags are on metal or liquid surfaces is a solved problem. See Omni-ID's tags for an example, albeit not for only a few cents, as the metal makes good RF performance a little more challenging http://www.omni-id.com/on-metal-rfid/

A store like CostCo that probably has a $5 minimum item price could be a good market for it.

my public library recently switched to this system I think, it used to be that you had to put each book one at a time on the self-checkout to "demagnetize" and orient it so it could read the barcode

With the new system you just pile all your books / dvds at once on the reader in whatever orientation and it checks out every one of them automatically, the slowest part is having to punch in the pin of your library card, next step I guess it could be having touchid on the reader or something along those lines

I work for a company that uses these chips (and others similar to them) for container tracking in everything from library books and clothes to vehicles and large container tracking.

Bay to Breakers is the iconic San Francisco race, with tens of thousands of runners (many in costume and some in nothing) running 12km across the city.

Thought it might get a NSFW tag, but it turned out to be hardware disassembler pr0n.

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