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.
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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Signing UpStep 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.
I only have the lock signal, if you get the unlock signal you could probably play it the same way.
final78.mp3790 KB
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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.