USB & Serial LCD backlight and contrast adjustment

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HD4478023-600.jpg

The adapter features software and manual backlight adjustment. Contrast is adjusted manually, but an optional hack can enable software contrast adjustment.

Backlight

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The backlight is software dimmable. The dim command sent from control software sets the backlight brightness.

A 100ohm potentiometer labeled BACKLIGHT can be used to add a resistor to the backlight if your LCD requires it. Please check the datasheet to see if a resistor is required.

Contrast

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LCD contrast is adjusted through a 10K potentiometer.

Software adjustment hack

An optional hack can enable software contrast adjustment. We didn't know if software contrast adjustment would work, so we used a solder jumper to make it a hackable feature.

Cut the trace between pads 2 and 3 of the solder jumper (SJ1). Next solder pads 1 and 2 together. The PIC's second pulse-width modulator (CPP2) is now the power source for the contrast. This is largely untested.