I just received my TFT LCD shield (go China!), and upon firing it up, it seems surprisingly dim to me. It's getting +5V to the BL pin, and seems to be generally working.
I know TFT's aren't the brightest, but it compares to my iPhone 4 at about 10% brightness setting (which I find unusable). :S Not great.
I'm just wondering if I got a dud, I'm doing something wrong, or my expectations are out of whack.
A dumb old 2x16 Hitachi LCD is way easier to see than this 160x128 TFT. Is that normal?
Wondering if I posted to the wrong place, or this is just a very inactive community. :S
My Esplora arrived from China, and I tried out the TFT on it. Still very dim, so it doesn't seem to be a problem on the Arduino end of things.
Tracing the circuit board, it appears that BL goes to a transistor (via 1k resistor), to switch 5V into the backlight, allowing an arduino to easily PWM higher currents than 40ma to the backlight.
Now, the strange thing is, the connection from the transistor to the backlight goes through a 330 ohm resistor (measures 329). At 5V, that means a max of 15ma to the backlight, which seems small (my Hitachi LCD draws 150ma). And if you're going to restrict the amperage to 15ma, why bother putting a transistor in there at all, the arduino could easily provide that amperage on an output pin without a transistor boost.
(There's also a solder-pad jumper allowing you to bypass the transistor, putting the 5V to the 330ohm backlight resistor. I'm guessing that won't help, since low amperate is likely my problem to start with? I might try another resistor in parallel with the 330ohm one, to see if it boosts the brightness. Awkward in my current setup, but I gotta try something.)
Just to make it a bit more visual, my board is a lot like this one:
You can see in a row from left to right, the LCD resistor, solder jumper, transistor. It's the value of that LCD resistor on other similar boards that I'd love to know...
The backlight circuit works like this, I think:
Pulldown resistor to keep it from floating, 1k current limiting resistor on the base, and a 1A capable transistor. Going into a 330ohm resistor. :S
Aaaaaand, I'll close out this lonely old thread with a solution, for the record.
I tried with various lower resistances, and ended up soldering on a 220 ohm, as per the original Adafruit design.
With that in place, things look way better, and the backlight seems to be drawing only 07ma (must be a current limiting resistor down with the backlight LED's). That additional 330ohm resistance was just dimming things to the point where it wasn't usable. Whoo-hoo!
It went from about the equivalent of an iPhone at 10% brightness (usable only in a dark room), to the equivalent of about 50% brightness, quite acceptable for a $12 display.
