Help Controling Monitors with an Arduino

[system]

Ok so here goes. I found this post on adding IR to a monitor. I really like the idea, but I want to change it a little. I have 3 monitors on my desk that I would like to control with a button matrix. I have 3 different model monitors, one is the same as the one that appears to be used in the post I linked.

Right now I have some questions that follow.

Q1) I believe I understand the circuit in the post I linked (shown below). The transistor is being used as a switch with the arduino sending a high signal to the base of the transistor to turn on the transistor. I can not make out in the picture, if the collector (far right) pin of the transistor is connected to the ground rail or the positive rail?

Q2) Secondly I have taken apart one of my other monitors. I will first describe the question then post images that will hopefully aid the description. This monitor is an older Samsung 245bw. It has 6 buttons (only 2 of which I would like to control), but only a four wire cable. I assumed they must be doing some type of multiplexing. So I measured the voltage values on key 1, key 2, and the two other pins. Looking at the picture below you can see the values I recorded. It appears that the two key lines are typically held at around 3v (when the monitor is on). The display board where the input board connects to must be reading the voltage and looking for changes.

Pressing certain buttons like say the input button results in the voltage of key 1 decreasing to 1.8v. Looking at the input board it appears this is done by having the switch connect an extra resistor of a given value (this allows them to achieve the different voltages by creating a voltage divider?). I came to this conclusion because the input board appears to have no components other than the resistors. For the other two lines I believe one may be there for powering the led, and the key lines, leaving the other unused, but I am not sure.
So do you think that is what is going on?

Q3) In my attempts to control the board I have successfully created button and transistor controlled voltage dividers. Ideally I would just solder an extra wire right on to the key 1 and key 2 through holes on the board, this essentially worked in the other post I linked, because he was just bringing the voltage to gnd or 5v. In this case however, I do not believe that is an option as it would result in the transistor controlled voltage divider having the same input and output (or being in parallel with an open circuit).

If I was to cut the wire connecting the input board to the display board I could put the circuit in series. Is this the best/only option for controlling the voltages on the lines and thus controlling the monitors power and input buttons?

Also is that a custom 4 wire cable or can I buy another (at a reasonable cost)?

Any other ideas / feedback?

Here goes the pictures
First is the voltages measured on the lines and an example drawing of the problem with only soldering to one point for each key. Also not No Change in voltage = NA

The input board BN41-00865A. It's glued to to the plastic backing

Attached some other photos that my be useful.

Also for the last picture (with the large connector) is that a safe place to tap into for gnd and possibly 5v to power the arduino?

Thanks for reading my long winded explanation. Can post more pictures if needed.

[johnwasser]

With NPN transistors the Emitter is connected to Ground. The Collector is floating when the the Base is grounded and grounded when the Base is energized (through a resistor to avoid excessive current draw).

That will work for buttons that connect a signal line to Ground. For a matrix keyboard where a button connects one signal line to another you need something like a relay or CMOS Bilateral Switch.

If the button voltage is 5V or lower you can directly use an Arduino output in place of an NPN transistor:

void PushButton(const int pin) {
    digitalWrite(pin, LOW);
    pinMode(pin, OUTPUT);  // Drive the signal line LOW (Ground)
}
void ReleaseButton(const int pin) {
    pinMode(pin, INPUT);   // Puts the pin in a high-impedance (near open circuit) state.
}

[system]

Thank You for your help John. My first question has been thoroughly answered.

As for the other two main questions, I have some new information. I have been able to control the on/off state of the monitor with the arduino and a transistor (used as a switch connecting key1 to gnd).

My real issue now is "pressing the input button" (changing the voltage on the key1 line from 3v to 1.8v). Is it possible to manipulate this voltage without putting a circuit in series?

Here is another shot at describing what I'm asking. Is it possible to only connect these two points (in the picture below) on the board to a circuit and change the voltage on the key1 from 3v to 1.8v?

[Paul_B]

OK, so you have discovered the trick of using two wires to sense six buttons (the other two wires are the indicator and the power button which is always independent). What you need to do rather than being concerned about voltages, is to measure the resistance that correspond to each button.

Then to emulate each button, you simply connect the corresponding resistor to an Arduino pin which is written LOW but defined as INPUT until you want that button to "press" when setting it to an OUTPUT pulls the resistor down.

[system]

Paul__B:
What you need to do rather than being concerned about voltages, is to measure the resistance that correspond to each button.

I was able to measure the resistances on the board. There are 4 resistors as you can somewhat make out in the earlier picture. Both sets seemed to have the same values (one for key 1 and one for key 2). I measured ~1.48kohms and ~2.66kohms. A voltage divider using those two values gives around 1.9v which is pretty close to the 1.8v of the key button. Flipping the two resistors in the voltage divider gives around 1v which is the other value I measured on the lines.

Paul__B:
Then to emulate each button, you simply connect the corresponding resistor to an Arduino pin which is written LOW but defined as INPUT until you want that button to "press" when setting it to an OUTPUT pulls the resistor down.

I am little confused about emulating the button. Wouldn't you need a voltage divider?

Edit: I was playing around with the circuit and I believe I now understand. Setting the pin to OUTPUT pulls down some voltage depending on the resistance connected. Looks like its somewhere around 2-3Kohms.
Edit2: After some testing 4kohms brings it right to 1.79v