Introduction: Shopping Cart Locker THE EASY WAY (Improved Range)

Picture of Shopping Cart Locker THE EASY WAY (Improved Range)

See my website for an even easier way. Lock The Cart

Many stores have installed locking wheels on their shopping carts that are supposed to stop shopping cart theft. The cart gets a signal when it leaves the parking lot and one of the wheels locks up. This instructable will show you how to forge that signal and lock up anybodies shopping cart where you want (works inside and outside the store).

This will work on any cart that has the solid wheel like shown in the picture below. These are the wheels that walmart uses. This method works the same way as the EMP Shopping cart locker but is way easier to make, however the range is far less, about 2 to 5 feet.

I made this a couple weeks ago and I saw the high power one today and decided to post mine. It consists of an mp3 player playing the lock signal attached to a coil of magnet wire. When the mp3 player and the coil are placed in my shoe I can step about 6 inches from someones cart wheel and their wheel will lock.

Note: The picture is using the old coil, which had far less range, the coil I am now using is about 30 turns around a 1 foot diameter, with nothing in the middle. This increased the range to about 4 feet.

Step 1: The Signal

Picture of The Signal

The signal is a 7800 Hz signal that I captured using a sound card and an aerial coil of wire at my local walmart. When amplified you can see that it pulses for certain periods of time. The locking signal is shown in the picture. I recreated it using a square wave and saved it as an mp3 file. Download the file (final78.mp3) and put it on your mp3 player.

I only have the lock signal, if you get the unlock signal you could probably play it the same way.

Step 2: How to Make It

Picture of How to Make It

What you will need:

Magnet Wire ( available at radio shack )

Right Angle Headphone Plug

Something round with a 1 foot diameter

Take your magnet wire (if you got it from radio shack use the green one) and wrap the whole spool around your round thing, making sure to have both ends of wire sticking out enough to solder, you probably want at least a foot sticking out. Should have about 30 turns. When the whole coil is rolled, wrap it in electrical tape to keep it together, but keep the end wires sticking out. You might want to take it off your round thing

Take a knife and scratch away the coating on the outside of each end wire about and inch down.

Take your right end headphone plug and cut off the casing. You should come out with something like the one in the photo. Solder either alligator clips or your actual coil wires onto the ground and left channel, as shown in the picture.

Step 3: How to Use It.

Picture of How to Use It.

Upload the mp3 file from step 1 onto your mp3 player. Put the volume all the way up and plug in your coil. Strategically place it in one of your shoes and step next to a shopping cart wheel. It may help to put the mp3 player on repeat. Takes a little practice to know where to step and for how long but its easy when you get the hang of it. Have fun!


CCube55 (author)2014-03-26

dose it matter left or right??

MFXPYRO (author)2012-09-12

Here's some info I sent a mate back in 2004 when I played with this :-

10/09/2004 22:02:40
Right you need to operate the HT12E at a clock of 1KHz which is off the graph
on the data sheet but looks to need a resistor (Rosc) of around 2.5Meg If
you've got a scope you can fine tune this but I don't think it's that
critical and the decoder should accept a bit of variance in the bit timing.
As for the data it's :-

D8=1 for Lock or 0 for Unlock
D11=1 for Unlock or 0 for Lock

Have fun!

In addition you need to modulate the data coming from the Holtek encoder IC at 9kHz (555 timer) and build a coil driver (I used Mosfets and Nicads) I emulated the encoder and modulator in an AVR to make it a single chip solution. BTW the address doesn't SEEM to vary between sites.

MFXPYRO (author)2012-09-12

Good to see this, I found out YEARS ago that gatekeeper wheels used Holtek remote control IC's (HT12X range I think from memory) so built a little black box unit with a mosfet coil driver. It worked well in the few tests I did but UK stores didn't widely adopt the system and the store I was going to try it at (a busy store) on the run up to Christmas :-) ripped it out and replaced it with a new system before I had a chance to cause widespread chaos. So my box has been gathering dust in a drawer. I may dig it out and post the details here if it's of any interest (although I suspect the microcontroller code I used to emulate a Holtek transmitter has been long since lost).

NozeDive (author)2012-04-01

Came back to this for some reason... Way too many people think that it's a sound that locks the carts. It's not a sound, it's a radio signal, so playing it on a loud speaker will not work.

swoodie2012 (author)2012-03-23

How do you connect wire to an mp3 player and would it work with an iPod Touch (no speakers). New to this.:)

NozeDive (author)2008-01-20

How the hell do you fit a one foot diameter coil in your shoe? Maybe you meant one foot circumference?

Shinji (author)NozeDive2008-02-16

Oops... See above.

ilpug (author)Shinji2011-11-10

the coil is flexible, so you could possible bend it into your shoe? huh, i was wondering that myself.

wouldn't it be possible when you are crossing the yellow line to disturb the signal with another signal of the same frequency??

it just makes the the range higher, however, if you could just time the phaze so it's the exact oposite of the line the signal will be disturbed

ilpug (author)damasta2011-11-10

so then hide the transmitter near the buried cable in the line, then you can take all the carts you want! (not that that is a good idea, at all, but just a random thing you could do, if you were so inclined)

ilpug (author)2011-11-10

reading down the comment chain, i got an idea: could you somehow play the locking sound over a megaphone or a PA system? that would be great!

d3monhax0r (author)2011-09-01

Does left or right matter?

rololo (author)2010-07-22

Hello, I need some help. My condo community has people that like to bring shopping carts into the community from the local supermarket. They steal the carts and use it around the complex and that makes our complex look ghetto. I've tried calling the market and a cart return company but they never pick up the carts. It's like they don't even care about how much money they are losing from these carts. Has to be like almost 10 here. I've started to unscrew the wheels on some carts but there are lots of carts that I can't get to unscrew the wheel cause there too tight. How do I stop these carts from working so I can just leave them in the dumpster area and so no on will use them. I think if they are left there then they are more likely to get picked up. Please help.

nabzaf (author)rololo2010-12-26

i used to use the left over cart by cut'n off the buggy part and keeping the base part add some plywoood and have a flower pot holder. then also came in handy when i had to help my buddy move his couch we fliped on thebuggy and just wheeled it out i put my grill on one many many uses for the old carts

mettaurlover (author)rololo2010-09-13

USE THE INSTRUCTABLE ON THEM. Just get them there, use the lock signal and leave them.

DavidKaine (author)mettaurlover2010-10-01

I'm pretty sure that if the carts have made it to the complex, they don't have locking wheels.

bjohn29 (author)2010-07-02

is there any way to make the range bigger???

YAY RANDOM ! (author)2007-07-05

it workes if u just record it on a mobile

jobergy (author)YAY RANDOM !2010-06-28

JUST GOT AN EXCELLENT IDEA FROM U RANDOM! you know the Walmart intercom prank? well find a new toy that can record sound, record the sound from ur phone [on speaker phone or whatever] and then some how place the ear part of the walmart phone on the toy and play it!?!?! i really hope that will work...definately gunna try it.

Alpha23 (author)YAY RANDOM !2007-07-05

u mean cell phone? O_o

YAY RANDOM ! (author)Alpha232007-07-06

yes (i'm british)

maker12 (author)YAY RANDOM !2008-01-02

random, you can put it on a phone but the coil will mess up the cell phone,s RF organs.

Shinji (author)maker122008-02-16

I think he means record the frequency with a cell phone's audio record function, you know? I wonder how well you could hear it while in a call...

abadon (author)2010-01-23

i have an idea on how you could increase the range. maybe you could add a small amplifier to the coil to amplify the signal.

struckbyanarrow (author)2009-12-19

i wrapped mine around a 6 inch long 1/2 inch diameter piece of pvc, i have not tested it yet but do you think it will work with pvc?

crazycarter29 (author)2007-07-15

what is the "Something round with a 1 foot diameter" is that the core you wrap the wire round, if so that must be huge, having a 1foot diameter. Plus what is magnet wire , can i use standard copper wire?

cowgomoo (author)crazycarter292007-09-25

its not worth it to use bare copper wire and plastic makes it less magnetic so it woudnt work. magnetic wire is $5 so if you can afford that go for it.

jongscx (author)cowgomoo2007-10-29

It's also called "ENAMEL COATED WIRE" or you could scrounge it off off some old speakers. (It is NOT however called "Speaker wire" as that's the wire you use to hook up the speakers with) Basically, it's a strand of wire coated with a thin, usually clear coat of varnish-like substance that insulates it yet keeps it still very thin. useful for when you need to wrap a bunch of wire in a coil to make an electromagnet but don't want too much bulk...

cowgomoo (author)jongscx2007-12-05

that would be too small diameter. you'd use a transformer for better results.

jongscx (author)cowgomoo2007-12-05

What would be too small of a diameter? Are you talking about the wire gauge or the coil?

If you're referring to the coil winding... I don't think I ever did, so I'm not sure what you're responding to.

Wire gauge-wise, smaller would be better, as small wires have less resistance and you would be able to use more of it without incurring significant bulk to your device (useful since we want to be sneaky about this).

Since you're using the output directly from the mp3 player, I don't think there would be an issue with it blowing the wire from too much current either. Maybe a PA system or a guitar amp... but not a MuVo.

Also, Magnetic field strength of a solenoid (a coiled loop of current carrying wire) B ="Mu knot * (I * N )/L" where I is the current and N is the number of loops. Small wire would lower resistance(allowing more current to pass) AND allow for more coils, which would both increase the field strength.

computer_freak_8 (author)jongscx2009-01-13

You contradicted yourself. You were right when you said "Wire gauge-wise, smaller would be better," but you were wrong when you said "as small wires have less resistance". The smaller the gauge, the THICKER the wire (larger diameter), which means less resistance. The SHORTER the wire, the less resistance, the THICKER the wire, the less resistance, and the LOWER the gauge, the less resistance. The gauge numbers are given by how many holes the rope of wire has to be pulled through during manufacturing. (Each hole in the series is a little bit smaller than the last.) At least, this is what I have read.

beaslera (author)jongscx2008-04-16

I am not clear what jongscx means by "small wires have less resistance", as the nominal equation for resistance of a wire is R = rho*L/A, where A is the cross sectional area, L is length, and rho is the resistivity of the material. So a thinner wire has more resistance. This relationship leads to a trade-off on the diameter of the wire; thicker wire allows fewer turns but can withstand higher temperatures and the lower resistance generates less heat for a given current.

NozeDive (author)jongscx2008-01-20

Would CAT-3 wire work? Once you remove the outer sheath and plastic insulator of each strand, I believe CAT-3 copper wire (telephone wire) has an enamel coating.

so on your website it says you can play this outloud? like i could trasfer that file onto my mp3 player and play it really loud on a pair od earbuds or put on cell phone and pretend its ring tone pleas reaspond. ~silver

Jdurban (author)2007-07-08

I was wondering how long it would be before someone starting doing this! My partners and I sold this company to Gatekeeper Systems back in '99. We got hosed pretty good in the deal and on the stock but win some lose some! I invented this technology over a decade ago and hold nearly a dozen U.S. and foreign patents on it. At the time it was a breakthrough design as there were no low voltage / low current Op-amps on the market yet. The first generation unit was built around a simple Cmos 4007 gate array! The loop driver produces an O.O.K. modulated 8khz carrier. The original design was modulated at zero cross to prevent artifacts that might leak into FCC part 15 ranges or above 9Khz. The reason for choosing the VLF frequency was to avoid FCC and other country's regulatory certification. I also designed the "Purchek" anti-pushout system and coined its name in 1997. The Carttronics wheel works the same way as it is the same circuit. We found 3 carts with missing wheels during our beta testing and later learned it was the guys at Carttronics. I also designed products for them. What can I say, it's an incestuous market! To see the patents just google "Jack Durban" or go to my old and crusty website that is soon to be updated with a couple hundred of my designs over the last 30 years... By the way... My new design is wireless and unlike the future Gatekeeper version does not relay upon goofy magnetic calibration markers or RSSI as a means of ranging and heading.Without the cost of expensive saw cutting to lay the signal wire in, this new technology allows even mom and pop stores to protect their carts. Product releases in early to mid 2008. The industry has been looking for an alternative for years. All the best, Jack Durban

evanwehrer (author)Jdurban2008-12-05

Thats amazing...

nak (author)Jdurban2007-07-14

neat :)

Jran Sakarra (author)2008-12-05

I gotta try this. My local card store I am at evey week is right across from a walmart thats uses this and we want to make one big enought to reach it from there.

damasta (author)2008-03-06

tip: you can get usable wire from an old speaker, transformer or a few million headphones

Xellers (author)2008-02-21

How can I download the mp3 file? I can't get it to work. Do I need Quicktime Pro?

TVRM (author)2007-08-02

What goes around comes around. Be nice to people.

Xellers (author)TVRM2008-02-21

being nice is good. However, playing pranks is quite funny. And anyways, I doubt that some random person who you pull this prank on will come back with a similar device to get revenge. Funny instructable lol ;)

Manic (author)2007-07-25

This really is a simple, but very good instructable. I've been looking for ways to install something like this in my car because it's always getting hit by rogue carts while I'm shopping.

leebryuk (author)Manic2008-02-17

Excellent Idea!

Mr. M (author)2007-07-14

hey ishtvan222, great instrucatable. I used it and it worked great. I was wondering if you would like me to feature it on my website?

Shinji (author)Mr. M 2008-02-16

You totally should, man.

grue (author)2008-01-10

u could make a super sized one that is big enough to kill all of the shopping cars in the country . that will be cool but you may get caught

Shinji (author)grue2008-02-16

I plan on making a giant one, and hooking it up to the amp in my Jeep. I oughta be able to put a whole Wal*Mart on hold for a bit, right?

pmac93 (author)2007-08-25

does polarity matter when hooking up the coil to the audio plug?

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