The first step in the process was to find the signal that they use to lock up the shopping carts. To do this i decided to make a coil antenna so that I could find the signal. The transmitter wire is not very hard to find, it is usually a back line around the edge of the parking lot. I have to admit you get lots of weird looks sitting at the edge of a parking lot at 3 am with a laptop in you hand and sitting on the ground behind your car..

Sitting on the ground behind the car getting the signal

The Signal Wire at the edge of the parking lot

The process to get the signal is rather simple, all you have to do is hook up the loop antenna into the audio input of your computer and use an audio recording program, i recommend Audacity (http://audacity.sourceforge.net/) After recording you should get a signal similar to the following: Wal-Mart unfiltered (Screen Shots Below) after doing a little signal analysis you should be able to get something more like this: Wal-Mart Filtered

Wal-Mart Unfiltered

Wal-Mart Filtered

After getting the clean signal the only thing that was left to do was to export that as an mp3 file onto the ipod. This file alone combined with the antenna that you used to pick up the signal works to lock up the shopping carts from a short distance. The next thing that I did in order to increase the signal strength was to build an amplifier to boost the signal.

Amplifier

After all of this was done all I did was put the ipod on repeat on the filtered signal and walk around the store, unfortunately i am only able to get about a foot range with this setup but I am planning on revising this to see if I can get more . I will keep updated if I do so. I am hoping to post a video sometime soon.

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The next test for us was to test the motors… 3 power supplies and some fancy daisy chaining, and a melted wire later… we found out that both of the motors do work, so it was not a total waste of time.

I have since gotten a new speed controller for it and hopefully will be having another post on here soon with the next step of this project. Any small additions I will update in my blog and once i get to the next step I will all the updates in a new project post.

Using RoboRealm I wrote a program that sampled an area of the floor in front of the robot, using this sample I compared the rest of the surroundings so this sample. Anything that was the same as the sample and not blocked by any other objects was considered “safe”. Using these samples it then chose the furthest “safe” spot and set that as the target. This routine is done over 3 times a second. This program created a basic obstacle avoidance.

I am planing and working on another RoboRealm project that I hope to have posted up very soon! I am also working on expanding my knowledge of OpenCV because of this project.

“The main purpose of this robot is object avoidance. The way that it works is by using a Ping ))) Ultrasonic Sensor mounted on a servo, this unit is them mounted on the front of the car. This works by taking 3 ultrasonic samples, Center, Right, and Left. It keeps driving straight until it finds something in its path, it then used the data from the last “sensing” of the left and right to determine which way to turn, if both paths are open it randomly chooses which way to turn, but if both sides are blocked it then reverses and tries it again to see if there is a better path. All of this is done without stopping between commands, thus the car never stops moving or slows down.”

-Well that was the original idea, But in the end, one of the major changes was that the speed that the car was traveling was proportional to the distance between the car and any other objects that may be in it’s path.

Here are some pictures of this project and some videos hosted on YouTube: