Riddle me this, Caped Crusader: Messages through the TV set

March 18, 2004
Most kids play with toys or watch television. But toymaker Mattel and its partner Veil Technologies hope that hordes of kids will soon be doing both at the same time.

Batman ($33) and his Batmobile ($52), two new toys from Mattel, will detect optically encoded messages and trigger signals embedded in "The Batman," a cartoon show from Warner Brothers coming this fall.

New action figures and accessories from Mattel, the Batwave line, will receive and decode messages embedded in video signals using techniques developed at Veil and used on The Batman, an animated television show. Text messages will show up on an LCD screen integral to the toy. The show will beam out information on characters and situations and will also transmit trigger signals for such tasks as turning the Batmobile's lights on and off, and firing its simulated lasers.

Messages pass from TV to toy digitally using subtle changes in the amplitude (or brightness) of certain lines on standard (NTSC) televisions, but the technology works with other formats, including the European PAL and Secam systems. Amplitude modulation is less than 1% and imperceptible to human eyes. No hardware is needed other than the toys. And a toy will respond as long as light from the TV hits its receiver.

"The NTSC TV picture is split into two fields," says Jim Withers, CTO at Veil Technologies. "We modulate alternate lines on those two fields. Viewers don't see the modulation because it is masked by underlying picture elements."

Data is encoded at 8 kHz and sent asynchronously at about 240 bit/sec, much too fast for humans to notice, and much too slow to send anything but simple text messages and triggers. A photodiode picks up the signal, which it actively filters and sends to a standard, off-the-shelf four-bit microcontroller that deciphers incoming ones and zeroes into a meaningful instruction set. Veil engineers worked hard to reduce the underlying code so they could use a four-bit rather than an eight-bit microcontroller. They also minimized noise in the optical signal coming through the diode so that they could use a less expensive op-amp.

"A photodiode has no problem detecting the carrier," says Withers, referring to the postage-sized optical pickup on each toy. "The diode senses all visible light, but active filtering narrows it down to just the carrier. For example, there's a strong 16-kHz component to every NTSC picture because of the line-scanning rate, and we filter that out. We also mask IR to minimize effects of sunlight and incandescent lights."

There are other methods of sending encoded messages over TVs, but Veil (short for video encoded invisible light) chose this one because the only equipment needed to receive it is an ordinary TV. "We could have put data in the vertical blanking interval, a signal used to synchronize the TV to the original transmitted picture," notes Withers. "But that's part of the inactive portion of the signal and not shown optically on the CRT. Users would need an inline decoder, like a cable box, to receive it. And from a business standpoint, using vertical intervals cannot be patented and anyone can put any data they want on it."

Veil researchers are already working on Veil II, and probably Veil III as well -- newer methods of sending more data through smaller pipes. Veil II uses the active portion of the video, like Veil I, but not optically. It will send data at 6 kbps and users will need an inline box that decodes and retransmits signals using IR, RF, or even Wi-Fi.

The new line of Batwave toys should be available soon, and the accompanying TV show, a product of Warner Brother, is slated for the fall. Warner hopes the technology builds excitement not only for the TV show, but for a Batman movie scheduled for next year.

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