# Ardunio, control of LCD TV power| Help with problems please?

#### lordphil01

Joined Dec 20, 2011
6
I am trying to use a Ardunio to control the power of a LCD TV (simple right?). To do this I cut the wire leading from the power button to the built in circuit board and put my Ardunio in-between. I connect the wire from the button to a analog port and read the signal I get from it. But the problem comes in that all I read is static! The board wont read the voltage coming from the button, I know that the button is sending a constant stream that is interrupted momentarily only when it is pushed down (which is how it is turned on and off).
What would you suggest I do to solve the analog read problem?

#### SgtWookie

Joined Jul 17, 2007
22,229
Are you powering the Arduino from the standby 5v? If not, how is the Arduino going to get power when the TV is off?

#### lordphil01

Joined Dec 20, 2011
6
Yes, as of now it is connected to a computer and receiving power through USB

#### lordphil01

Joined Dec 20, 2011
6
Do you think the voltage it is reading may be to high? And I need a resistor?

#### SgtWookie

Joined Jul 17, 2007
22,229
Measure the voltage from the TV chassis ground to the computer's chassis ground.

The TV is probably using the neutral wire for "chassis ground", where your computer is using actual earth ground - if you're in the States. Even a fairly light load on the neutral can make a noticeable difference in the voltage between the ground wire and the neutral wire.

The ground wire is never supposed to have current on it. It's there for protecting humans only.

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#### lordphil01

Joined Dec 20, 2011
6

That is a link to a picture showing my setup.
Thank you for the info on the ground differences, assuming that is the problem (At the moment I don't have a meter to test the voltage) what could I do to change the ground of the chasis so that it may be in sync with that of my computer, or visa versa.
In other words could you put it into laymans terms of what needs to be done?
Thank you for your help so far!

PS extra info:
I am using a OSEPP mega 2560 which is a board that is very similar to the Ardunio mega. I am using the Ardunio v1.o compiler.
And for now I am not outputting anything, just trying to read things properly.
My code : (if it helps at all)
int val = 0;

void setup()
{
Serial.begin(9600);
}

void loop()
{
Serial.println(val);
}

#### lordphil01

Joined Dec 20, 2011
6
And one last thing, this has been bugging me, but I had it working properly not to long ago. I had the board reading values and outputting them to the LCD board, and it worked exactly as I wanted. Then (with out warning, or me changing anything in the setup) it wouldn't work any more. :/

#### SgtWookie

Joined Jul 17, 2007
22,229

That is a link to a picture showing my setup.

Thank you for the info on the ground differences, assuming that is the problem (At the moment I don't have a meter to test the voltage) what could I do to change the ground of the chasis so that it may be in sync with that of my computer, or visa versa.
You need an isolation transformer to plug the television into; then you can ground the television ground to the computer ground.

The other way to do it would be to use a laptop on batteries; as batteries are isolated from the power grid.

I am using a OSEPP mega 2560 which is a board that is very similar to the Ardunio mega. I am using the Ardunio v1.o compiler.
And for now I am not outputting anything, just trying to read things properly.
My code : (if it helps at all)
Rich (BB code):
int val = 0;

void setup()
{
Serial.begin(9600);
}

void loop()
{
Serial.println(val);
}
I'm not familiar with Arduinos. I hear they're popular, but don't know their features, nor what you need to do to initialize them, nor what the C library functions are.

#### SgtWookie

Joined Jul 17, 2007
22,229
And one last thing, this has been bugging me, but I had it working properly not to long ago. I had the board reading values and outputting them to the LCD board, and it worked exactly as I wanted. Then (with out warning, or me changing anything in the setup) it wouldn't work any more. :/
Either a wire broke, you lost a control voltage somewhere, or your LCD died.

#### lordphil01

Joined Dec 20, 2011
6
I tried disconnecting my laptop from the wall, to no avail.

And also to you saying the LCD tv died, here is the weird thing. I was having this problem before, then it magically went away, and now it is magically back. With no changes to the setup....

#### SgtWookie

Joined Jul 17, 2007
22,229
Things don't just happen "magically" - there is a reason for whatever happened. There is likely a bad solder joint that changes connectivity over temperature.

You posted a blurry photo of something that had wires marked over with a blue Sharpie to indicate analog in, analog out going to somewhere else, and the power switch. Aside from that, I couldn't tell much.

Something on the TV chassis needs to be called ground. You need to find what that is, and reference your Arduino's ground to it.

#### thatoneguy

Joined Feb 19, 2009
6,359
I can't see your photos, as that domain is blocked by WOT (Web Of Trust) for malware, probably not yours, but it got flagged due to somebody using it.

Anyway, back to the TV...

You stated you were having problems before you started, were those problems like TV would work for a while, then quit, and if you shut it off for a bit and turned it back on it would work for a while, then quit? Then now it doesn't turn on at all? --THIS IS IMPORTANT

What were you getting the serial data from/to on the Arduino? What make/model is the TV? Do you have a scope to see what the signal on the line is? It may not be (most likely isn't) UART.

Lastly, why are you wanting to physically power it off and on with the Arduino? Why not just use the IR Remote signal for off/on?

#### stirling

Joined Mar 11, 2010
52
Apart from everything already mentioned... particularly earth...

You're general plan seems to be: have the arduino read the analogue voltage input so you can then after some programatic control have the arduino output that same analogue voltage to turn on your TV. Beside it being a questionable plan - the arduino's "analogue-out" is NOT an analogue voltage - it's PWM - the arduino has no DAC.