Back Light
Home Up PIC Programming Back Light PCB Prototype

 

 

LCD Back Light Driving: 

Not backseat driving. But close.

Nothing like pumping 60V AC out of SMD devices.

 I've got an LCD with a backlight that I want to mount onto a printed circuit board. It is quite a chore to excite this Electroluminescent Backlight enough to light up. The recommended Back light driver (the chip that causes the back light to illuminate) was much too large and way too expensive (see wire-wrap prototype). So let's build our own!

Here you see the LCD attached to the BL (Back Light) circuit. The masking tape was only holding the wires in place for soldering. No, it's not just held together with bailing wire and duct tape.

A nice close shot of the components. You can all most see the lamp driver, the inductor, and the diode is buried under a lump of tape.

Notice the ice cream in the top right corner. The only way to prototype SMD (surface mount devices) is at midnight on a good sugar high. It really wasn't too bad. Once I got a nice soldering iron and a super fine tip, anything was possible.

There it is. An EL Lamp chip attached to a 180uH inductor and a MiniELF diode.

These three things (and a small 100nF capacitor) replace the big honkin' black box on the wire-wrap prototype. The BL driver on the wire-wrap board is the biggest part on the board. It's labeled 'NDL-202' and cost three times as much as the parts shown above (including the quarter).

It's nice to know that recommended part and part values from datasheets actually work! The screen is not quite as bright as I would like, but this is simply a change of the inductor value. Nothing that cannot be changed on the fly.

Now it's off to make a PCB!