Picture of EMP shopping cart locker
Ever noticed a painted yellow line in the parking lot around many supermarkets and retail stores? The magic yellow line emits a signal that causes carts to stop dead in their tracks, preventing carts from leaving the parking lot.

Now you can build your own portable yellow line-- with up to a 20 foot range. Need I say more? Hint: it works inside the store.

Disclaimer: This is not an easy project. It will require knowledge of circuits, soldering, social engineering, and a tiny bit of PIC microcontroller stuff. High power is involved, and if you mess up, you might get burned, caught on fire, or arrested-- most likely all three. Always use an appropriate amperage fuse to prevent a short from becoming a much bigger problem. This project is also fairly expensive. The parts will cost about 65 bucks. Batteries with some kick will run 20-30 bucks, and a single PCB is about 60 bucks. They get a lot cheaper if you buy multiples for your friends.

We would be thrilled to sell kits, and it would certainly make the components cheaper and easier to get, but frankly, we're a little worried about the possibility of civil action. We likewise recommend that no one else sells kits commercially.

In order to remain as anonymous as possible, we have utilized Tor. Tor is a network anonymizer which sends packets through a convoluted network to its destination in order to avoid tracing. We aren't lawyers, and who knows what lawyers are capable of these days, especially with things like the DMCA and recent controversy over data retention requirements likely to be instituted in the EU.

With the warnings out of the way... In the wise words of Norm Abram, "Be sure to read, understand, and follow all the safety rules that come with your power tools. Knowing how to use your power tools properly will greatly reduce the risk of personal injury. And remember this: there is no more important safety rule than to wear these-- safety glasses. Let's get started on today's project."
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ewilhelm7 years ago
CCube551 year ago
anyone got anything for those antitheft beeping thing by the store entrance??
Just use a normal magnet a few times on one of the fancy bar code things that are inside of movie cases.
gee7 years ago
Using the information posted here, I've created my own small/portable version. It's built with: - An Atmel ATTiny45 microcontroller. 8 pin DIP. - An IXYS IXDD414 FET driver, capable of driving +-14A peak. 8 pin DIP. - A series RLC tuned circuit at 7800Hz - a 1.5 ohm series resistor, a 1.0uF/100V capacitor (bipolar plastic), and a 390uH ferrite rod inductor (Coilcraft PCV0) - And additional bits; a 78L05 regulator for the AVR, a couple shottky diodes to protect the FET driver, a 9V battery clip, a couple large, low-ESR capacitors on the 9V input, pushbuttons, etc. Range is about 30 feet ;-) If you're building one of these, using a tuned LC circuit is the way to go - you can get large currents oscillating in the output inductor without requiring substantial average current draw from your battery; a rechargeable NiCD/NiMH 9V battery with a large capacitance across it is sufficient. Only thing is, a tuned circuit can generate upwards of 100V. So don't touch any of the output circuit bits when you've got the thing turned on. Also, grab a copy of LTSpice or other circuit simulator and model your output circuit - inductor, capacitor, series R, and don't forget to include include the R inherent in the FET driver and inductor. You'll want to set your Q high enough so that you get a good resonance going on, but not high enough so that the circuit takes forever to start up and decay. After all, you have to pass 250 baud on/off keying through the circuit. Happy mischief.
Cfichman gee2 years ago
can I pay you to make me one? I'm not that technically inclined. whatever you think is fair.
iNate3 years ago
Vary funny but I can't try it don't have these here. Why do we need these? Why steal things its stupid and disrespectful. Get a job you bums! and a shopping cart
of all things that are stolen a shopping cart why.
brian20127 years ago
just wondering, will that set off those sensers by the doors that some items have in them
iNate brian20123 years ago
magnets-no circuits just plain old magnets (those thick plastic stickers with a bar code on them, sorry no pictures)
If you take an old one and slide it over a magnet lots of times, in the same direction it will set of the alarm again (re magnetizes it) If you slide ti back and forth a lot of times it wont set of the alarm (demagnetizes it)
btop brian20125 years ago
u know it always sez that past the damned line the trolley will stop i wonder what really happens?
ilpug3 years ago
heres an idea for concealment: if possible. build it into a purse! understandably it is only good for a girl, but who would expect a purse?
ilpug3 years ago
well, this has got to be the best prank i have seen. unfortunately i am to dumb to pull it off just yet. i will wait a few years and do this once i get my engineering degree, if its applicable by then.
savagesteve7 years ago
I like the Aldi Grocery store method. It uses simple human psychology. The carts are chained together. You stick a quarter in a special slot on the cart to release it. When you are finished with the cart, you re-attach the chain and it releases the quarter. Okay, 25c doesn't sound like much money, but there's an innate human need to get that quarter back! Shopping cart thievery is just sad. It makes about as much sense as stealing a gas pump handle.
In the UK it's a Pound, and in Europe it's a Euro. I guess everything is cheaper in the USA! It did create a huge market for little keychain coin-sized tokens for them, though. I was thinking of selling bags of the right sized washers for £1 a hundred.
To be fair, nobody here carries coins larger than a quarter. We have $.50 and $1.00 coins... but they never caught on. If they were common I'm sure our cart lock/unlock mechanisms would require a bit more money.
I like the Jewel (albertsons/cub/sav-on/ect) method. Don't expect all of your customers to rob you.
thats if one uses that pump handle to throw at some doumbass that just cut you off the road...........
Xellers5 years ago
This is very nicely done - but it would be hard to explain if someone caught you with a circuit board and a bunch of wires under your shirt...
LkArio5 years ago
You're awesome!!! I love this, LOL
Zerotology5 years ago
About the bike lock. Simple solution. When the bike is in motion, there's plenty of energy to charge a battery. Or, You could have a solar cell. All you'd need is enough current to trigger a transistor which disconnects from a magnet lock and the mechanism drops into place. Well, I guess the bike would be in motion so it would have to act upon centrifugal energy to lock.
willwade7 years ago
If these pictures don't make a security guard want to call the counter terrorism unit I don't think anything will.. i.e. does this not look highly suspect in the current day of people wrapping themselves in dodgy looking wire and detonators? All you need to do to finish the look is make sure your pulling this stunt with some fertiliser in your trolley and hey presto the next day you find yourself in Guantanamo with a orange jumpsuit.. God forbid if you mention Allah..
I guess since all mighty Obama closed Guantanamo, we shouldn't have to worry about that now. ;-)
alexhalford7 years ago
can someone please explain the difference between an NPN transistor, a PNP transistor and a FET / MOSFET. Thanks
I believe that all of the components (electronic, that is) in this inst require a thorough understanding of flux capacitors. After that, it's all downhill ice skating.
Indeed, doc. Once you deal with gigawatts of power, you can do anything.
Gigawatts, I can deal with. Jiggawatts, on the other hand...
i think NPN transistors let current through when electrisity is flowing into base. PNP transistors let current through when there is no electrisity flowing into base. I could be wrong though
thanks, what about FET / MOSFET though???
FETs let current through the Drain-Source channel depending on how much voltage is between the Gate and the Source. They are also know as unijunction transistors, as opposed to NPN/PNP trannies which are Bijunction transistors. I think MOSFETs are good at handling high currents.
Field Effect Transistor and Metal Oxide Semiconductor Field Effect Transistor.
I am fairly sure that they are the same thing
fet and mosfet are different from npn or pnp um
canida7 years ago
Wow. I'm in awe.
drcrash canida7 years ago
Yeah, me too. What a an incredible bunch of vandals and vandal-worshippers you guys are. Blaming the engineer for not making a cheap little simple gadget un-hackable? Yeah, that makes sense. Why not blame the guys who design housepaint mixes for not putting in Teflon, when you deface somebody's house and your obscenities stick, and cost the homeowner time and money? It couldn't be the vandals' fault, for vandalizing. No, it must be the fault of people who didn't invest a lot of time and money in making things immune to vandals. Hey, why not blame the engineers who design freeway overpasses when you drop cinder blocks on the cars passing below? They're just asking for people to drop cinder blocks on people, aren't they? Losers. Maybe it's not "theft," because you don't profit. Maybe it's just vandalism, which is arguably worse, in a way. It's purely malicious, rather than self-interested. How lovely. Maybe people should do the smart thing, and make you unable to vandalize---by putting you in jail. That is what jails are for. They're to keep antisocial people away from people who have better things to do than deal with petty criminals messing with them for no good reason.
Vandalism involves destroying property. I would rank TPing a house a far more grievous offense than locking carts. It's probably less obnoxious than flipping off the lights when you're on the toilet.

Where did we blame an engineer for making the system too easy to hack? We didn't. We're engineers. We understand what decisions go into making products, because that's what we do.

Below 9kHz is an unallocated frequency range (FCC regs). This low a frequency forces data to be transmitted pretty slowly. One way communications also usually makes the system susceptible to being fooled with a false signal. Given the circumstances, the engineers made all the right decisions.

I would estimate that our cart locker project has been used less than a dozen times in the 5 years that it was being worked on. It was usually taken out to test it, to show friends or, as last time, to get pictures for the Instructable. In general we do have more productive things to do, like finish grad school. We probably wouldn't have ever shared how to make one of these with the world, but a laser cutter was up for grabs. Maybe your assessment of not self-interested needs to be revised.

It is our hope that people will have learned something from this, be it something about signal analysis or one of the many aspects of power electronics. The board, as provided, makes a beefy H-bridge capable of controlling around a 50 volt, 30+ amp motor. Do with it what you will.

Maybe interested readers (and there are many, look at the hit count) will have learned that there's an overabundance of internet ethicists out there. It is likely the ethicists will have learned nothing, only exhausted themselves spraying their stink glands everywhere.
Actually vandalisim covers more than breaking things. It is grafitti and the shopping carts dumped in to water ways and all the other stuff people do because they just do not give a monkeys squirt about other, the costs that they incurr that are PAID BY THE TAX PAYER!!!! and you complain about your tazes, well this is why, people see this activity as "Getting back at the system" sorry to burst that particular bubble but what you are doing is increasing everyones tax liability including your future liability that you have just added to. If morons would just pull their heads out of their own A'hole world for a second and look at the bigger picture, all you are doing is giveing the system justifaction to keep on increasing taxes and pushing up the cost of living. Nice one. As for the arguments its not theft and its not vandilisim & no one gets hurt... sorry to burst your bubble but in law it is and people do... Prices go up you *ricks..
Eh? So the Walmart guys go to the government and ask for new trollies? Are you nuts? The Walmart people pay for new trollies, not the government. And why would they buy new trollies? Used once or twice a year, no-one is going to connect this with anyone or anything, it's hardly malicious, and only a detailed traffic analysis of the CCTV will trap the person doing this. I can see from your British flag that you might be in the UK. Even over here, the government only pays Tesco indirectly. I suggest your ire be directed at stopping our tyrannical government from passing more oppressive laws, rather than people pranking shoppers in another part of the world.
You obviously do not understand or comprehend the system. It is simply this... You unlocak and take a trolley, you dump it when your bored with it, the store loses and has to replace the trolley. In the mean time, the city refuse collection system recovers said trolley and disposes of it. The tax payer picks up the bill. The difference is the cost, while a new trolley costs as little as £75, to dispose of it requires considerably more resources like the manpower and machinery involved in its retrieval and disposal. Think my last council had a ball park figure of £1,500 cost in retrieval and transport, handling and disposal of of one trolley. This is what gives the city the thumbs up to raise taxes. This applies to anywhere in the world. If you didn't unlock the trolley and take it, the shop would still have its trolley, the tax payer would not be burdened the costs of recovery, transport to the disposal point, etc. Thats the bigger picture and your obviously blinkered to this fact. What may appear to be a good prank, it has hidden costs. As for directing me to my own government, what's that got to do with the price of beef?
Our own government (not that I voted for the PM, but who did?)

Anyway, you are still crazy. This is about locking a trolley, not unlocking a trolley. Or did you forget to read the Instructable?

Further, the store who owns the trolley is responsible for it's collection - that's why they have little vans and "If I'm lost" stickers on them to get them back.
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