I'm talking about Banksy's "Girl with balloon" painting that shredded itself at auction.

I think the general consensus is that he didn't, and that it was set up before the auction (or a couple years ago, not 12 years). But lets say he did, how could he have made it keep its power for that long? What sorts of RF receivers run on such low power? What batteries can withstand a 12 year low-but-constant-load life?

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    Hypothetical question so pretty pointless and opinion based IMO. – pipe Oct 19 at 9:08
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    Another thought: A simple passive AM receiver that needs no batteries. You transmit an AM signal that wakes up the coded receiver. If it wakes it up accidentally, no problem as it was only on for a few seconds (or less.) – JRE Oct 19 at 9:15
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    The problem is not with the receiver, which runs on very low power. The problem is with the shredder which requires much more energy. – Christian Lescuyer Oct 19 at 11:29
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    I hadn't heard about "12 years" in the news. I'm sure I could look it up but, for completion & context, could you tell us in the question a little more about why the RF receiver would have had to run for 12 years? – Lightness Races in Orbit Oct 19 at 12:17
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    While the answers here are all interesting, the simpler explanation is that Banksy's group "Pest Control" was given the painting before the auction to verify its authenticity. Presumably they could have added fresh batteries. – mbrig Oct 19 at 14:17

A relatively large lithium primary cell would be my choice. They are specified for something like 10 or 20 year life running water meters, including periodic radio communication. And maybe a second cell to run the motor so it stays relatively fresh.

The Israeli company Tadiran makes such products.

As long as the temperature does not get too high the shelf-ish life of such Lithium cells is in the decades (they claim 40 year operating life). You can bet that an expensive piece of art will be kept in carefully controlled temperature and humidity conditions.

Given that power source, power management would be important but not crazy critical. You would want to keep the average draw in the << 100uA range most likely. Doing the sums, their 19AH TL-4930 works out to 54uA (average) for 40 years. So even if it turned on a receiver once per 10 minutes for a second it could draw tens of mA, provided the sleep mode power was inconsequential.

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    I just replaced a LiSoCl2 primary cell from 1993 (backing RAM) which was still at 3.69v. Interestingly, the German manufacturer (sorry, light blue, forget brand, "L" logo?) had the exact same wording written on it as Tadiran's cells. I wonder if it is the same company. – rdtsc Oct 19 at 10:19
  • @rdtsc Maybe Lenovo? They bought them PC part of IBM in 2005 - so that device would be IBM. LG is Korean. (Lenovo is not German either)... – Volker Siegel Oct 19 at 10:34
  • @rdtsc Tadiran was apparently bought by Saft Group. For whatever reason, Saft batteries have an LS logo. Is that it? – Spehro Pefhany Oct 19 at 10:39
  • Aahhh it was a "Sonnenschein Lithium" brand. Google finds some images from "SL-770". – rdtsc Oct 19 at 16:27
  • Another point to add - there are chips with extremely low-power wakeup receivers. They typically run on a "sniffing" schedule with a very low duty cycle. For example, this chip is intended for use in pacemakers, and averages 300 nA with a one-second sniff interval: microsemi.com/document-portal/doc_view/134304-zl70103-datasheet – Peter Oct 19 at 18:36

The most likely answer is that he didn't. While that was the claim, it is much more likely that he swapped out the frame soon before the painting went up for auction. Dave Jones from the EEVblog did a video on this:

https://www.youtube.com/watch?v=SdKdQWhlNTY

UPDATE Here's a follow-up video from the EEVblog:

https://www.youtube.com/watch?v=8dbYGefDdWo

Why would it be a low-but-constant-load life?

Assuming the auction takes hours, it would be enough to awake the RF receiver once every hour for a few ms to check for an RF signal.

The transmitter would either transmit the RF signal: - For a complete hour, knowing the RF receiver will be awake at least once - Know in what time period (like every whole hour) the receiver will be awake and send it within that time.

In both ways, the transmitter can continuously send the message, only the receiver needs to receive it only once.

** Update after James Trotter's remark **

New algorithm:

  • As above but with the following addition
  • Every hour it checks for an RF signal, except it doesn't start shredding, but after this signal it starts checking every 10 seconds (for let's say the next 10 minutes). This Awake Often signal can be send multliple times.
  • Directly after the auction a Start Shred command is given which is received by the painting and shredding starts.
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    And, you can shut off the receiver entirely if the picture hasn't moved in a day or two. The receiver only needs to be on if the picture has moved. If it's hanging quietly on the wall, it isn't at auction. If it is moved around, it might be on the way to auction. – JRE Oct 19 at 9:12
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    Or something low tech like the old pinball machines used. Just a weight on a wobbly spring that closes a contact if it wiggles. – JRE Oct 19 at 10:33
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    @Alephzero: Mems accelerometers are active devices that require power to detect motion. The old wobbly spring types don't consume power until they are moved - they are completely passive until motion causes the contact to close. – JRE Oct 19 at 11:37
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    The painting shredded seconds after the auction finished, it would have been highly coincidental if its hourly wake up happened to coincide with the end of the auction – James Trotter Oct 19 at 12:32
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    Using a rarely-polled signal to turn on more frequent polling would make it easy to reduce current draw to essentially nothing when used with batteries that have enough current-handling capacity to operate the cutter mechanism. As EEVblog noted, however, the painting was delivered to Banksy's associates for authentication very shortly before the auction, so the mechanism could easily have been installed at that time. – supercat Oct 19 at 22:01

Passive RFID tags run on zero batteries. The RF signal itself carries sufficient energy to power the RFID tag.

Now we know that a big battery had to be present for the shredder, but we can use a small wakeup circuit to keep that battery entirely disconnected for years, and only connect it when the passive radio receiver is energized.

  • Lol, can you imagine if some random guy nearby was screwing with a software defined radio and somehow accidentally tripped the thing in that time? Even better if it shredded on its way past the gallery kitchen with the dodgy microwave running... – James Trotter Oct 19 at 12:33
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    @JamesTrotter: The simple bit is just to power up the wakeup logic. That's typically smart enough to do a simple tag match ("Is this a request for me?"). That's not going to match for stray RF radiation. Even if it did, you presumably have a bit stronger check further down the line (count number of repeats, require the specific tag to be seen N times in a row while powered up). That might just a microcontroller, but it will rarely if ever be woken. – MSalters Oct 19 at 12:39
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    oh, I know, but the thought of a naive implementation still amused me. – James Trotter Oct 19 at 12:41
  • @Keeta Have you found a citation for that? As of right now that statement is marked as "citation needed" on Wikipedia, and as mentioned in another comment, it didn't seem like there were any cables when they took it down. – JMac Oct 19 at 17:39

Primary cells, a arming switch, and non-rf method of control, like IR, as there was a plant in the audience. They could easily sit for years and still be good. It was discreetly armed right before auction.

But as Banksy's instagram video showed, it didn't work right. In rehearsals it shredded it completely. This is likely due to how long the batteries sat in the frame. Even top quality Alkaline primary cells would show signs of aging 10 years later, enough for large motors to only work half of their intended job.

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