strange behaviour with ac/dc adapter

Hello everybody and happy new year :wink: ,

I've been having a problem with my TFT 7 inch touchscreen.
The problem is when i plug in my TFT module with the shield through USB cable, the module works fine, but when I try to connect it with ac/dc adapter, the screen does not work, I only can see lines and white screen.
This only happens when I connect an AC/DC adapter, the adapter is 12V and 800mA, that it is suppossed works fine with arduino, and arduino has a voltage regulator so this shouldn't be a problem.

Has anybody had the same problem or has anybody how to solve it??
This is the Shield I have (but version 2.2):
http://www.elecfreaks.com/store/lcd-tft01-arduino-mega-shield-v20-p-214.html

Any help would be appreciated, because I need to use touchscreen with an ac/dc adapter.
Thanks in advance!.

that it is suppossed works fine with arduino,

Can you be more specific ?
Are you saying that the Arduino works with the ac/dc adaptor plugged into it ?
Have you measured the output voltage of the adaptor ?
What is the connection between the ac/dc adaptor, the Arduino and the TFT (ie: where did you get the adaptor and
what was it made for , as in , why are you using it ? ) Did it come with one or the other of the above ?
Why 12V ? That 's right at the upper limit. 9V would be my choice. I think the Arduino can take up to 12V.

Try measuring the voltage at the Arduino 5V pin, see what it says.

If the voltage regulator burning hot?

12V is a lot, you might need an external regulator. The one on the Arduino is tiny.

Hello,

Try measuring the voltage at the Arduino 5V pin, see what it says.

If the voltage regulator burning hot?

I´ve measured the voltage in the voltage regulator of the arduino and the Vout is 4.96V, I also measured the voltage in the voltage regulator of the shield and I have a Vout of 3.96V.
The voltage regulator seems not to be hot with this voltage of 12V.

Are you saying that the Arduino works with the ac/dc adaptor plugged into it ?

The arduino works fine with this ac/dc adapter, because I've used it without TFT display, the problem is when I plug in the display the display do strange things, like blinking, and white screens. If I load any example sketch with the same adapter the arduino works fine.

Have you measured the output voltage of the adaptor ?

Yes, I've measured the output voltage of the adapter and this is 11.7V.
I've also tried with another adapter 5V, 800mA and the behaviour is the same, the display do the same strange things.
And I'm using this 12V adapter because if I use the 5V adapter the voltage is 4.6V and I think is not enough for the arduino.

I do not know what is going on, because I've measured the same things with arduino connected via USB cable and the values are the same, but when I plug in the arduino with the adapter happens that in the TFT display.

I also measured the voltage in the voltage regulator of the shield and I have a Vout of 3.96V.

This is not a normal voltage. If it is a 3.3V TFT the voltage should be 3.3V. If it is a 5V TFT , the voltage should be
4.85V to 5.10V. 3.96V is neither of these. Why isn't it in the correct range for a 5V device ?
Is it possible for you to plug the TFT into a breadboard instead and power it with the 5Vdc 800mA supply ?

Hi again, raschemmel,
The TFT is a 3.3V display because uses SSD1963. I've been watching the datasheet and this value is accepted by the SSD1963 chip.
The maximum ratings for this chip are, from -0.5 to 4.6V.
Anyway, if i connect USB cable the voltage is the same and the TFT works, the thing is I don't understand why does not work with adapter if the voltage values are the same. It should work, isn`t it?

The problem is when i plug in my TFT module with the shield through USB cable, the module works fine,

Can you post a photo of the TFT and a link to the datasheet ?
You are referring to it as a shield so that means it has pins on the bottom to mate with Arduino UNO correct ?
If it is a 3.3V SHIELD then the voltage it is using is coming from the 3.3V pin of the UNO , NOT the 5V pin. There should
be no connection from the 5V UNO pin and the input power to the shield , since it should be connected to 3.3V.
(5V is > 4.96V which you stated was the MAXIMUM for the TFT ). You need to measure the voltage on the 3.3V pin and the
+5V pins of the Arduino for the following FIVE cases:
CASE 1: NO TFT CONNECTED/USB CABLE CONNECTED
CASE 2: TFT CONNECTED/USB CABLE CONNECTED
CASE 3: NO TFT CONNECTED/USB CABLE CONNECTED WITH AC/DC POWER SUPPLY CONNECTED
CASE 4: TFT CONNECTED/NO USB CABLE CONNECTED WITH AC/DC POWER SUPPLY CONNECTED
CASE 5: NO TFT CONNECTED/NO USB CABLE CONNECTED WITH AC/DC POWER SUPPLY CONNECTED

I don't have the TFT now here, but tomorrow I'll post a picture of the TFT, and I'll measure the voltages as you say.

5V is > 4.96V which you stated was the MAXIMUM for the TFT

CORRECTION:
CHANGE TO : "5V is > 4.6V which you stated was the MAXIMUM for the TFT "

Sorry, I forgot the datasheet, I attach the datasheet of the chip.
And this is the link:
http://www.microtipsusa.com/pdf/SSD1963.pdf

And here I leave a link to a TFT display I've got:

SSD1963.pdf (1.69 MB)

akompe:
I´ve measured the voltage in the voltage regulator of the arduino and the Vout is 4.96V, I also measured the voltage in the voltage regulator of the shield and I have a Vout of 3.96V.

OK, so what's the voltage when it's powered with USB?

You need to find the difference between the two.

Hello,
I do not remember now what was the voltage, but I have also tested the voltage when it is powered with USB, and I think is the same value.
I measured the voltages powered with usb and powered with AC/DC adapter, and is the same I think, but I will tell you tomorrow more accurate.
Thanks

AT WHICH SHIELD PIN ARE YOU MEASURING THIS 3.96V ?

In the Vout pin of the voltage regulator the shield has.

Every pin of an Arduino has a name. I am asking you the name of the pin that the shield regulator vout is
connected to . What is the name of the pin that THAT pin PLUGS into on the Arduino ? (Look at the labels
on the Arduino ) Is it the pin labeled "3.3V" or is it the pin labeled "5V" ?
If you can't follow the traces you need to put you meter in CONTINUITY CHECK mode and check from where
you are measuring the power (with the power off of course since you are measuring continuity, not voltage)
to the pins on the shield . When you identify the pin that voltage is connected to then look at the label on
the Arduino to find out which pin it is. You are telling me that you are measuring the Vout of the module
regulator but where is that regulator getting it's Vin ? (ie: one of the shield pins ?, which one ?)
(3.96V is too high for 3.3V and too low for 5V).

Attached is photo of your shield.
Can you post a photo of how you have it connected to your Arduino
or post a wiring list that shows which pin is connected where ?

  1. The backlight power requirement is a 5V power supply, which draws around 500mA current at maximum brightness. Make sure you use a external power supply for Arduino DUE and MEGA2560, USB power is NOT enough.

  2. The power supply should be 6V-9V to prevent overheating of the linear regulator on MEGA2560 which will cause instability. If you use MEGA2560 R3 version, use a 7V power supply.

Items 1 through 4 in the attached Read_me file are also important but note item #6.

Read_me.txt (2.59 KB)

Hi again raschemmel,
Yeah, this is my TFT display, but not my shield. I'm using a shield to connect display to arduino, and this shield is this:
http://www.elecfreaks.com/store/lcd-tft01-arduino-mega-shield-v20-p-214.html

When I refer to the shield I am refering to this. And it is supposed that this shield makes the conversion from 5V to 3.3V needed for the display.,that's the reason why the shield has a voltage regulator.

I have also seen that the display has another voltage regulator, I've measured the voltage in that regulator Vout and I've got 1.18V that is in the range of voltages admitted for the SSD1963 (this voltage is connected to Vcc of the IC)
I've measured the voltage in the pin of 3.3V from arduino and I've got 3.27V (normal).

Make sure you use a external power supply for Arduino DUE and MEGA2560, USB power is NOT enough.

About this, I said with USB works correctly. Maybe my AC/DC adapter has too much current (800mA), because I've read in some post USB power is about 500mA, and if it works with USB but not with AC/DC adapter, maybe could be the 800mA current from adapter, this is I could be going on I think.

Hello,

I have solved the problem. It seems the problem was the voltage of AC/DC adapter, it was too much voltage. I have tried with a DC power supply and a voltage of 7V and a current of 1A and it works!! :D.

Anyway, in the pin labeled as 3.3V of the display there's always 5V (4.95V), it is a thing I don't understand because if it is labeled as 3.3V it must be 3.3V instead of 4.95V.

I'll try to find an AC/DC adapter of 7V or 9V (better if is 7V, because I've noticed if I use 9V the voltage regulator of arduino heats) and I will try it.
I've also noticed the voltage regulator of arduino heats with this current (900mA) but if I use lower current the display does not work.
Is it possible to change the voltage regulator for another one greater??

Thank you, for your replies.