(Obsolete) USB Power Supply for Video Sunglasses

This web page is obsolete and will no longer be maintained.

Many commercial video sunglasses with a hidden CCD or CMOS camera, as used by blind users of The vOICe, are analog devices that need a separate video capture device plus a separate power supply for interfacing with a notebook PC. There exist various convenient USB video capture devices for getting the analog (NTSC/PAL) video signal into the computer, but it would be most convenient if video sunglasses could also be powered directly by the notebook PC or netbook rather than having to use a separate (rechargeable) battery pack for the glasses. This page describes a simple solution that gets around the need for a separate battery pack altogether by using a commercially available cheap USB DC-DC converter and an adapted USB extension cable.

A regular USB port has four pins: two for 5 volt DC power and ground, and two for data. Video sunglasses typically require a DC supply voltage well above 5 volt, such that the 5 volt of a USB port does not suffice. With many video sunglasses, the allowed supply range includes 9 volt DC. Please check the technical specifications of your choice of video sunglasses: on this page we will assume that the video sunglasses accept a 9 volt DC supply voltage while drawing a current of less than 300 mA (milliamp). So then we need a device that converts a USB port's standard 5 volt into 9 volt for the video sunglasses. Technically such a device is known as a DC-DC converter or voltage converter, and fortunately a suitable USB DC-DC converter is on the market in the form of a phone charger accessory. Specifically,  Zip-Linq (Zip-Linq Europe formerly at www.ziplinq-europe.com) sells the "9V Nokia Booster for Wireless Phone Charger" (the ZIP-CELL-B9V with 5 VDC 450 mA input and 9 VDC 380 mA output; update: this particular device now seems out of production, but you may still be able to find some vendors that have it in store). Clearly this device is meant for charging certain Nokia phones and for nothing else, but its specifications suit our purposes just as well. The Zip-Linq device is a tiny block, somewhat reminiscent of a USB memory stick, that plugs right into a regular 5 volt DC (500 mA) USB port on the PC, and on the other end it has a regular female USB plug again, but now at a higher voltage, namely 9 volt DC (300 mA). Be warned that you should never plug any regular USB device into this other end! Such an unfortunate mistake is easily made because the plug does physically fit any normal male USB plug, while the upconverted higher supply voltage would likely cause significant equipment damage and even fire hazard. You should in general also not make use of a self-powered USB hub, because it typically can deliver only about 100 mA maximum per port instead of the 500 mA of a normal USB port, and 100 mA at 5 volt gives just over 50 mA maximum at 9 volt.

Wire color Function Red   +5V supply White   Data − Green   Data + Black   Ground

The next step is to cut a regular USB extension cable in two, and use the end with the male USB connector for making a lead that will connect from the 9V USB output to the video sunglasses. Specifically, after splitting the four thin wires and shielding near the cut in the USB extension cable, you need to solder the thin red (plus) and black (ground) wires to the (barrel) connector typically used to power analog video sunglasses. This too needs to be done with great care. The USB wires tend to be very thin and fragile, and afterward wrapping some supporting tape around the soldered connections will not only serve to prevent a current short but also help prevent the wires from breaking during wearable usage later on. You should ensure the correct voltage polarity for the video sunglasses, which is best done by first using a voltmeter to measure the correct polarity while the glasses are powered by the 9V battery or battery pack as provided by the vendor of the video glasses.

Finally, it is advisable to fix (tape or glue) the modified USB cable to the USB DC-DC converter to minimize any chances of inadvertently connecting a regular USB device to the output of the USB DC-DC converter, of course assuming here that the barrel connector used to power the video sunglasses will also not get connected to any other devices that might have a plug of the same dimensions.

Most or all USB video capture devices will readily connect to the video signal lead of your video sunglasses, but the power lead connecting the USB voltage converter output to the video sunglassses' power supply connector needs to be assembled as indicated above, because such a lead is not (yet) available on the market.

Now, one can create a convenient wearable setup for daily use of The vOICe with video sunglasses, with everything powered by the portable PC's built-in battery. A representative wearable setup for The vOICe will thus comprise a notebook PC or netbook inside a backpack. A USB video capture device and USB power supply (the voltage converter) are plugged into two separate USB ports on your notebook PC or netbook. The USB video capture device captures the video signal from your video sunglasses, while the USB power supply powers your video sunglasses. Stereo headphones plug right into the headphones connector of your notebook PC or netbook.

Application note: the approach described above can according to user reports also be applied with the Lego Mindstorms NXT brick (normally powered by 6 AA batteries in comsumer version) and the Lego NXT Camera (9 volt camera with wireless NTSC transmitter).