The Great Backlight Liberation Begins

There’s a small market in LCD panel controller boards. When we salvage a panel from a retired laptop, we can enter its model number into eBay. If the panel is used in a high-volume laptop (for example, one of Dell’s consumer Inspiron laptops. Or most Apple MacBooks) then someone is likely selling a driver board that accepts HDMI input and translates it into the signal to control a panel’s integrated electronics.

I had salvaged the panel from one of my old Dell Inspiron laptops and, buying one of these adapter boards for $50, converted it to an external monitor. Eventually it became the onboard screen for Luggable PC Mark I. (Mark II used a commercially available monitor, and stories on both are available here.) A few months after that adventure, I received another retired Inspiron laptop and used its screen for the Portable External Monitor project.

I have several more LCD panels salvaged from retired laptops, but I don’t need very many external monitors. Furthermore, resolutions on these panels were lower than 1920×1080 limiting their utility. It’s hard to justify spending $50 for a circuit board to hack-up converted laptop screens when a Full HD 1920×1080 desktop monitor can be had for about $100.

I had thought it might be interesting to build my own LCD interface boards, but there are several obstacles. One is the requirement to build connectors to carry high-speed raw pixel information, which is tricky to do correctly given the high bandwidth translating to low tolerance for sloppy work. The LVDS (low voltage differential signaling) system doesn’t connect directly to typical microcontroller output pins, but translator chips are available and some task-specific microcontrollers have integrated LVDS output.

But the biggest hurdle against building my own boards is documentation. The protocol carrying that high-speed raw pixel information is a mystery. Counter to popular electronics convention, datasheets for panels aren’t distributed freely online. Many of them are proprietary and difficult to get, others lie behind paywalls. It makes sense to pay if I’m designing a device using millions of panels, but it doesn’t make sense if I’m fiddling with a single panel.

So those salvaged LCD panels have sat in my workshop, gathering dust waiting for a new purpose in life. Now that I’ve successfully extracted and illuminated the backlight module from three different LCD panels, I believe I have found that new purpose. Utility of extra monitors quickly pass a point of diminishing returns, but gentle diffuse white light sources are far more useful in wider variety of settings. No need to buy $50 driver board makes this a lower cost project, combined with higher utility of diffuse white light sources means the great backlight liberation begins.

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