$25 Head-Mounted Display

So it’s 2007: shouldn’t there be more cyborgs? Well, for a mere $25.00 (or less), you can be one big step closer to being one yourself. How so, you ask? Click the following link to to find out!
A few months ago, the rather clever folks at Wild Planet released a nifty (though rather clumsily named) little “toy” called the “Spy Video Car”. I cannot stress enough how well engineered this gadget is. For around $100 (much less on eBay), you get:

• A nicely-styled motorised car base with decent-for-a-toy steering and an almost silent powertrain
• A two-channel R/C set, also of decent-for-a-toy quality
• A color capable video transmitter/receiver with a few hundred feet of range
• A miniature B&W CCD video camera (similar to one of these)
• A very bright 8mm IR LED and, best of all, a…
• A video headset containing a Kopin 300M B&W LCD screen, optics, backlight, and a PAL/NTSC driver board

This guide will be all about re-purposing the later, though I will do similarly for the camera and video rx/tx set eventually. I should also mention that you can buy the headset separately here , but please don’t be greedy as I don’t think they’ll last long. What’s interesting is that the “replacement” headsets I bought are newer and much improved versions of the original one included with the car (one would assume that the newer cars come with the newer headsets, but I cannot verify this). The original one had a poorly diffused, red backlight which made made for a rather bad display all around. In the new version, they have upgraded the diffuser and changed the LED to white–making it look similar to an older camcorder’s viewfinder. They were also kind enough to redesign the circuit board into something much more hack-friendly. The most obvious of these changes is the potentiometer in the upper right-hand corner of the board (see below)

Turning this little critter adjusts the gain–an adjustment my headset needed pretty desperately. Oh, but I’m getting a bit ahead of myself, aren’t I?

First off, let’s talk about how to hook this bad boy up. Because Wild Planet decided to use normal video standards, we can make this usable without even opening the casing–heck, with the right adapters, you could probably do it without any soldering! Either way, you will need three things: a way to connect to your video source, a power supply, and a way to connect it all to the headset . To connect the headset to a DVD player, VCR, game system, iPod, PC, etc., you’ll probably want to use an RCA cable. If you don’t have one laying around, you can get one at most good dollar stores. As for power, the headset has a 3.3v regulator built in so you can run it on a wide range of things. It originally ran on 9v, but anything between 3.3v and 12v ought to work just fine. Wiring three “AA” batteries in series will give you around 4.5v, which is a good balance of physical size, battery life, and voltage. To connect this all to the headset, you’ll want to find a female 3.5mm 3-contact phono jack–better known as the thing you plug stereo headphones into. I’d snag a connector out of an old walkman or something if you don’t have a free one laying around. The pinout for the headset’s plug is as follows:

 

The base of the plug is the ground. This will need to be connected to two things; the negative terminal of your power supply and the shield of your RCA plug (when you strip the cable, this will be the woven sleeve around the inner wire). The middle ring is the video, which connects to the center wire/pin on the RCA cable/plug. Finally, the tip connects to the positive terminal of your power supply. Double-check your wiring, plug the RCA cable into your composite video source, and connect your power. If all goes well, you should see an image! Now if you’re video device is PAL format (from Europe, UK, etc.), you’re done! If, however, you’re device is NTSC (American), you’ll notice that the image in the headset is a bit messed up. Most modern devices will have a software setting somewhere that will let you change the video format, but there is a pretty simple hardware solution if not. Let’s have a look at that solution, shall we?

First, we need to crack open the display housing. It’s glued shut, so prying is our only option (unless you have a sonic screwdriver, that is). Insert your presumably non-sonic screwdriver into the side with the cable coming out of it and pull away foreward (away from your face, if you were wearing it (which you really shouldn’t be at this point)).

Ignore the way I’m doing it in the photo above and do it on the side with the cable. I managed OK, but there is a risk of hurting the LCD’s delicate ribbon cable if you jam sharp instruments into the side I did. The cover should pop off, leaving you with this:

The bit we need to get at is hiding under that capacitor in the lower right, so gently bend it out of the way. There you will see a surface-mount resistor and two blank pads. The datasheet for the chip (Kopin A300) tells us that the pin those are connected to is the PAL/NTSC setting. To switch it into NTSC mode, simply remove that resistor. If you want to be extra thorough, you can desolder that resistor and move it onto the blank pads as shown below:

Doing this will pull the line low, whereas just scraping it off lets the line float. It seems to work fine either way, but it can’t hurt to play it safe. The “resistor” seems to be little more than a jumper, so you can actually just pop it off and bridge the blank pads with a bit of wire or solder if you’re lazy (like me).

Pop the lid back on and there you have it: a wearable screen that can be connected to just about anything that plugs into a normal TV–and for less than twenty-five bucks!

So, what’s next? Well for one, you can make the display mush less dorky looking by removing the guts, rearranging them, and cramming them into something else. Sunglasses, perhaps? You can also probably replace the optics with something sharper and/or thinner. You could also forgo the whole HMD idea and turn it into a tiny projector–maybe with a laser for a light source? Electrically there is a lot of fun to be had as well. The data sheet for the chip shows us that there are are several unused functions such as black and white level and gamma adjustments, the pads for which are easily accessibly on the back of the board. There’s also the VERY intriguing “OSD_in” pin that may prove to be fun. Does anyone know what kind of signal that takes? I can’t seem to find any standards…

Good luck and enjoy!

---

Possibly related posts: (automatically generated)

• Video card, Mother board Blows
• Australian 180SX
• Oh baby….