Augmented Reality (AR) on mobile devices has grown in leaps and bounds as the devices have become more powerful. However, these devices have not yet reached the point where they are capable of high quality markerless AR. To solve this problem it was decided to build a prototype tablet system that has the needed processing power to be used for AR research. The base of the prototype tablet system is an Asus G51J-3D laptop which uses a Core-i7 processor and NVidia GTX 260M which provides ample processing power to implement high quality markerless AR.
This post documents the building process of the prototype tablet system and also serves as a guide for others whom want to attempt the same.
Disclaimer: This will void your warranty and could lead to personal injury if something goes wrong. We cannot be held responsible for any damages or injuries.
As always before anything can be designed you first need to know what is available to work with. Therefore the first step is to take the laptop apart so that we can see what there is to work with. We start by removing the screws hidden behind the rubber pads as shown below.
The Asus G51J laptop
The rubber pads hiding the screws
After all the screws have been removed the next step is then to unclip all the small plastic clips around the screen. The easiest way to do this is to insert a small flat object, such as a flat screwdriver or a cut credit card, at one side and run it along the edges to pop the clips open.
One of the clips that need to be unclipped
You should now be able to remove the front part of the bezel. Before we remove the back panel we first need to check how the back panel is attached to the screen and if there are any other device that need to be removed first. In our case we had to remove the webcam and the PCB for the back panel lights.
The PCB for the back panel lights
The bottom screw holding the back panel in place
The top screw holding the back panel in place
After these components have been removed we can simply unscrew the back panel and pull it loose from the sticky panel attached to the back of the LCD. We also need cut the wires connecting the Wi-Fi and Bluetooth antennas so that the back panel can be removed. Now for the big moment: Checking if everything is still working.
The back panel removed
The screen image is still nice and crips
The LCD panel from the back
Luckily (in our case) everything is still working, as it should. So after removing the hinge covers, let’s take a look at the wires that connects the LCD to the rest of the laptop. Normally one would expect a ribbon cable running from the LCD to the laptop. Unfortunately this is not the case with our laptop as we found a collection of loose wires instead of a ribbon cable. These can still be extend, but it is not as simple as with a ribbon cable where one can simply buy a longer cable and replace the existing one.
The connector on the left side of the laptop
The wires that need to extended
A couple of things to keep in mind when extending the wires:
- Try to keep all the wires more or less the same length to minimize signal disturbances.
- If wires are grouped in twisted pairs, then it is best to extend them in twisted pairs.
- Try and match the wire types. (E.g. Use multi-core wire to extend multi-core wire.)
- Try and test after every extention so you’ll know which wire caused your problem should the screen not work.
- Try and stagger the joints of the different wires. This will prevent having a big bulge at a single point in the cable.
- Make sure you insulate the soldered joints of the wires. Using heat-shrink is probably the easiest option.
- Make sure all power is switched off. Remove the battery if possible and disconnect the cable connectors for added safety.
- There is one other issue that might arise during testing: Blowing the motherboard. This issue did arise during my extension process. It occured when I attempted to straighten a bent pin in one of the connectors. Luckily the motherboard could be replaced (Thanks Jacques, Mike and Oliver for your help!)
The completed cable extension
If the extension is short you should have minimal issues, but with a longer extension, as per our case you might start experiencing image degradation due to the varying cable lengths during the extension process. Below are some of the issues that you might experience.
Out of sync image
- Colour shifting
One final addition that is worth considering is strengthening the soldered joints using glue or some acrylic medium. We used nail polish since it is acrylic based and easy to apply (and remove if need be).
Reinforcing the joints
Once you know what you have to work with its time to tackle the design problem. The design will depend on what you want to do and which tools you have available. In our case we decided to use stereo cameras (which needed to be swappable between two different sets), accelerometer and gyroscope sensors and a touch screen add-on. Each of these components needed to be taken into account during the design process. Since we have access to the university workshop for machining we were able to create a simple design using a few pieces of machined polycarbonate. Polycarbonate was chosen since it is light, easy to machine and has good mechanical properties. The model of the design for one of the stereo pairs can be seen below.
The screen side
The camera side
As you may notice the wires have not been included in the model. The reason for this is the difficulty to model wires and in most cases it is simple enough to make an estimate of the space required for the wires and at assembly make the necessary adjustments to accommodate the wires. Below are the pieces of polycarbonate we machined.
The middle Polycarbonate panel
The back Polycarbonate panel
Sensor and PS3 Eye mounts
The sensor mounting consists of the two sets of sensors which we will use to determine motion and an Arduino to send the sensor data to the laptop. The first set of sensors is a cheap commercial 3-axis accelerometer and 3-axis gyroscope and the second set is a more expensive inertial sensor.
The sensors assembly
Tip:Use masking tape to colour code the headers
The next assemblies are the two stereo camera pairs. The first consists of two PS3 Eye cameras that will be used to test cheap consumer cameras with the system. The second is a pair of Basler 311fc cameras that are of a much higher quality, but also much more expensive. Due to the long connectors used on Basler cameras, the cameras cannot be placed as close to the tablet as the PS3 cameras and are therefore mounted on an aluminium L-section.
The PS3 Eye mounting
The assembled PS3 Eye stereo pair
The Basler stereo pair