The GTFT backlight control does not appear to be working for me. I cannot turn the backlight off. The product page says "The LED backlight is dimmable by PWM" http://arduino.cc/en/Main/GTFT (part number A000096)
I only have one unit, so perhaps there is something wrong with the one I have, but I assume the BL pin is supposed to let you turn the backlight off and on, and that the BL signal being high will turn the backlight on. (The Esplora schematic shows the BL pin shorted to +5V).
While investigating this problem, I found that the GTFT schematic symbol for T1 (used to turn the backlight off and on) is for an N-channel MOSFET, but the part numbers (PMV48XP / FDN340P) are P-channel MOSFETs. A P-channel MOSFET would have an integrated diode in the opposite direction of what is represented in the schematic, so +5V would always be connected to LEDA. That's what I'm seeing. The backlight is always on and when I change the BL signal from low to high it just slightly changes the brightness.
So I think that either T1 needs to be changed to an N-channel MOSFET, or (perhaps a better option, but without going into a lot of detail why it is better) the source and drain pins on T1 need to be swapped. In the latter case, the pulldown resistor (R3) should probably become a pullup and you might want to put a BJT on the gate to reverse the signal polarity (so BL high will turn the backlight on).
Sooo.... I guess I'm looking for the forum to either let me know whether this is a widespread problem or just a one-off with my particular unit.