Shopping Cart Locker THE EASY WAY (Improved Range)
3 Steps
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.
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Step 1: 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.
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MFXPYRO says: Sep 12, 2012. 5:09 AM
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 :-

A0=1
A1=1
A2=1
A3=1
A4=0
A5=0
A6=0
A7=0
D8=1 for Lock or 0 for Unlock
D9=0
D10=0
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 says: Sep 12, 2012. 4:56 AM
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 says: Apr 1, 2012. 9:38 AM
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 says: Mar 23, 2012. 4:41 PM
How do you connect wire to an mp3 player and would it work with an iPod Touch (no speakers). New to this.:)
NozeDive says: Jan 20, 2008. 6:17 AM
How the hell do you fit a one foot diameter coil in your shoe? Maybe you meant one foot circumference?
Shinji says: Feb 16, 2008. 11:18 PM
Oops... See above.
ilpug says: Nov 10, 2011. 7:35 PM
the coil is flexible, so you could possible bend it into your shoe? huh, i was wondering that myself.
Feb 21, 2008. 10:59 AM
wouldn't it be possible when you are crossing the yellow line to disturb the signal with another signal of the same frequency??
damasta says: Mar 6, 2008. 2:54 PM
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 says: Nov 10, 2011. 7:34 PM
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 says: Nov 10, 2011. 7:31 PM
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 says: Sep 1, 2011. 3:28 PM
Does left or right matter?
rololo says: Jul 22, 2010. 6:06 PM
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 says: Dec 26, 2010. 8:31 PM
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 says: Sep 13, 2010. 7:07 AM
USE THE INSTRUCTABLE ON THEM. Just get them there, use the lock signal and leave them.
DavidKaine says: Oct 1, 2010. 3:46 PM
I'm pretty sure that if the carts have made it to the complex, they don't have locking wheels.
bjohn29 says: Jul 2, 2010. 10:51 PM
is there any way to make the range bigger???
YAY RANDOM ! says: Jul 5, 2007. 4:38 AM
it workes if u just record it on a mobile
jobergy says: Jun 28, 2010. 4:55 PM
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 says: Jul 5, 2007. 6:19 PM
u mean cell phone? O_o
YAY RANDOM ! says: Jul 6, 2007. 3:00 AM
yes (i'm british)
maker12 says: Jan 2, 2008. 6:39 AM
random, you can put it on a phone but the coil will mess up the cell phone,s RF organs.
Shinji says: Feb 16, 2008. 11:21 PM
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 says: Jan 23, 2010. 2:11 PM
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 says: Dec 19, 2009. 5:05 PM
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?
Jdurban says: Jul 8, 2007. 12:40 PM
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... www.vorel.com 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 www.vorel.com
evanwehrer says: Dec 5, 2008. 6:31 AM
Thats amazing...
nak says: Jul 14, 2007. 3:57 AM
neat :)
Jran Sakarra says: Dec 5, 2008. 4:00 AM
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.
TVRM says: Aug 2, 2007. 7:30 AM
What goes around comes around. Be nice to people.
Xellers says: Feb 21, 2008. 3:07 PM
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 ;)
damasta says: Mar 6, 2008. 2:58 PM
tip: you can get usable wire from an old speaker, transformer or a few million headphones
Xellers says: Feb 21, 2008. 4:54 PM
How can I download the mp3 file? I can't get it to work. Do I need Quicktime Pro?
Manic says: Jul 25, 2007. 10:41 AM
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 says: Feb 17, 2008. 2:32 AM
Excellent Idea!
Mr. M says: Jul 14, 2007. 2:39 PM
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 says: Feb 16, 2008. 11:24 PM
You totally should, man.
grue says: Jan 10, 2008. 4:05 PM
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 says: Feb 16, 2008. 11:19 PM
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 says: Aug 25, 2007. 10:29 PM
does polarity matter when hooking up the coil to the audio plug?
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