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1  Using Arduino / Displays / Re: womarts LCD touch on: January 16, 2013, 04:55:09 pm
Hi Deltac0.
I'll be very interested to hear how you go.
2  Using Arduino / Displays / Re: womarts LCD touch on: December 31, 2012, 11:07:48 pm
Hi again,

What's with the backlight/fade control mod?  Do these things typically have backlighting issues?

No issues, just that with this controller you can't control the backlight or turn the display on or off.
(ie: the .lcdOn() and .lcdOff() library functions aren't implemented for this display)
A simple hardware mod and optional (still not finalised) UTFT library mod allows this, but you need to have access on the display board to an extra PWM digital line from the Arduino. Also need space to solder 1 transistor and 1 resistor.


3  Using Arduino / Displays / Re: womarts LCD touch on: December 31, 2012, 03:28:53 pm
How did you go with this? It looks tempting, not only for the price, but also because shield and display are integrated in a single board. I have the Sainsmart which is bulky and could be less reliable with the extra shield layer.
On the other hand, doing the backlight fade/control mod on this board may be difficult.
Cheers, Bernie.
4  Using Arduino / Displays / Re: TFT becomes pixelated and goes white on: December 30, 2012, 09:10:40 pm
I'm new with the arduino, but one comment you made in your post seems odd.
I use a pot to reduce VCC to 3.3v
Do you mean that a pot is your method of reducing 5v to 3.3v? ... Or is the pot controlling some king of regulator?
If the former, I'd be surprised if it worked very well.
5  Using Arduino / Displays / Re: Can the Sainsmart 3.2" TFT be turned on & off? on: December 28, 2012, 08:38:37 pm
No worries, beige and kerryjosper. It ended up being exactly what beige suggested. The only improvement to this might be a FET instead of the transistor, as suggested by MarkT.
6  Using Arduino / Displays / Re: Can the Sainsmart 3.2" TFT be turned on & off? on: December 27, 2012, 03:45:44 pm
I've created a new thread that describes how to fade and control the backlight because although the info came from this thread, it's actually a slightly different subject to controling the display and modifying the UTFT library.
It's here.
cheers, Bernie
7  Using Arduino / Displays / Re: Can the Sainsmart 3.2" TFT be turned on & off? on: December 26, 2012, 01:12:22 am
Some progress.
Thanks to all, I have a simple mod that allows me to control the backlight (on/off only, no fancy fading) using a spare digital output pin.
The transistor is necessary because the backlight draws close to 100mA. The digital outputs can source (or sink) a maximum of 40mA. There could be tears..
Remove the trimpot, solder 1 x PNP transistor and 1 x resistor (nominally 1K)
In the attached circuit diag and code example, I've used digital pin 8 to control the backlight.

Software still isn't entirely resolved, though I have a simple workaround.
I'd like to use guix's UTFT library mod, but it doesn't seem to toggle pin 8.
I don't yet know enough about writing to these port registers to change it nor can I find good docs about port/pin mappings.
( I WILL fix this because it's a better way to do this).
For the moment though, I left guix's library mods in place (they seem to shut down the display, though not the backlight) and added a line in my arduino sketch immediately after the call to turn the LCD on or off.
       const int backlight_pin = 8;
       const int backlight_on = 0;
       const int backlight_off = 255;


        analogWrite(backlight_pin, backlight_on);         


        analogWrite(backlight_pin, backlight_off);         

8  Using Arduino / Displays / Re: Can the Sainsmart 3.2" TFT be turned on & off? on: December 25, 2012, 06:47:57 pm
Thanks beige,
I thought of using a FET because the response might be more linear and wouldn't load the PWM line?

>>pop a PNP transistor in the place of the pot controlled from a PWM source
I'm not overly skilled in analog electronics, but I thought NPN would work. Collector connected to +ve 3.3V, Emitter to the backlight control line (pot removed) and Base to the PWM output via a 1K resistor.
.. it didn't work  smiley-sad
regards, Bernie
9  Using Arduino / Displays / Re: Can the Sainsmart 3.2" TFT be turned on & off? on: December 25, 2012, 08:54:39 am
Happy Christmas (athiests and all smiley-wink ) and thanks for the replies.
A MOSFET might work.. thanks for the suggestion.
I'll investigate guix's code and minor hardware hack first since it's less "invasive".

Actually, a combination of both suggestions might give "fade" control: I wonder if a FET-based circuit could be used to replace the pot..?
Perhaps later.

>>PS, I have exactly the same display, do you also have about 1 to 2mm slack at the left side, that you have to press to get uniform lighting?
You mean physically put pressure on the edge of the display nearest the 40-pin conn?
... I looked closely and I can see that edge is raised about 0.5mm above the PCB.. perhaps by the flexible flat-ribbon that bends around beneath it.
I can press this gently down at each corner and it extinguishes the light that seeps out from beneath.
In my case it doesn't have any visible effect on the screen lighting however.
In the attached photo, you can see that the plastic frame around the display is intended to locate into the small hole on the PCB.
Perhaps holding each corner down after applying a small drop of CA glue (a.k.a. Superglue) might help if it affects the lighting on your display?
thanks again,
10  Using Arduino / Displays / Can the Sainsmart 3.2" TFT be turned on & off? on: December 24, 2012, 04:05:40 pm
Hello all,
I bought a Mega2560 with the 3.2" Touch screen and shield from Sainsmart to build a vehicle battery monitor. Everything has worked amazingly well and with all of the info and code libraries around getting most things running has been fairly quick and easy! However, since this monitor will run 24/7, I'm concerned about the lifetime of the touchscreen and backlight. Does anyone know of a way to turn this screen off & on? The .lcdOff() and .lcdOn() functions don't work with this model. Even a hardware mod would be acceptable. :-)
cheers, Bernie
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