LCD panels don’t emit any mild themselves. In a totally darkish room, you wouldn’t be capable to see something proven on an LCD display except there may be an added mild supply — a proven fact that annoyed many Sport Boy homeowners within the ‘90s. To make LCD panels brilliant, TV and monitor producers add backlights that shine white mild via the screens. However that ends in uniform brightness, which not often matches the onscreen content material. To unravel this downside, Mousa constructed his personal full array native dimming LED backlight so as to add to his current LCD TV.
This concept isn’t new and many high-end TVs have been offered with this know-how for a few years. By placing an array of LEDs behind the display, it’s potential to regionally alter the backlight brightness to go well with the content material. Black areas can have their backlight LEDs turned off solely, whereas white areas can obtain full brightness on the identical time. Nevertheless, we’ve by no means heard of anybody retrofitting a TV with this function. It’s advanced, doesn’t match into a normal enclosure, and requires the backlight LEDs to react to the onscreen content material.
Mousa pulled this off by first constructing a brand new enclosure with extra space to accommodate the LED array. That enclosure is wooden with the TV’s authentic plastic bezel body glued on.
That gave him room for the array of 98 CoB (Chip-on-Board) LEDs, organized in a 14×7. After they’re all on, they devour the same quantity of energy as the unique backlight.
From there, Mousa confronted his greatest problem: controlling the LEDs based mostly on the incoming video content material. One would possibly envision hacking the TV’s management board to faucet right into a video sign or one thing, however the true answer is each jankier and cleverer.
Mousa began with an HDMI splitter, with one aspect going to the TV’s enter. The opposite aspect goes to the enter of a management board pulled from an inexpensive LCD projector. With the projector’s LCD nonetheless connected, Mousa had a duplicated view of the video content material. He then positioned a 14×7 array of LDRs (light-dependent resistors) on a PCB that mounts over the projector’s LCD. That array matches the LED backlight array and the LDR at place A1 controls the facility going to the LED on the identical A1 place. The LDR controls the LED energy by feeding into the gate of a transistor.
So, a really brilliant space of the LCD projector display will trigger the LDR to ship full energy to the corresponding LED through the transistor. The other is true for very darkish or solely black areas of the display.
This truly works very nicely, but it surely isn’t good. The most important downside is decision, as 98 LEDs don’t come anyplace near matching the two,073,600 pixels of a full HD TV. That ends in plenty of mild leaks, so brilliant spots produce a type of “halo” that spreads over into darkish areas. Even so, Mousa’s work right here is extremely spectacular and the implementation is ingenious.