Shopping Cart Locker THE EASY WAY (Improved Range)

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Introduction: 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

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

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.

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!

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    80 Comments

    dose it matter left or right??

    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.

    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).

    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.

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

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

    2 replies

    Oops... See above.

    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??

    2 replies

    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

    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)

    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!

    Does left or right matter?

    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.

    3 replies

    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

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

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

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

    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.