Reading the LED status of an external circuit?

Other Hardware General Electronics
1

I'm currently working on a little learning project, where I want to replace the bi-color LEDs on an original Xbox with RGB LEDs controlled by a Nano.

While it's easy to just remove the LEDs and hooking the new RGB ones up to the Nano and fade colors, I also want to listen to system errors and change the color or blink. The front panel LEDs of the Xbox usually light up or blink in a certain pattern if something is wrong with the system.

Therefore my plan was to read the value of the front panel pins which are normally conntected to the LEDs.
This is how the front panel looks like:

681×521 59.2 KB

The Arduino will later on pull the power from the Xbox itself, so they share the same GND.

But I'm currently too inexperienced to get a grasp on reading the values from one of the anodes or rather the pins later on since the LEDs will be removed completely.

First of all the Nano is currently hooked up on a little breadboard and it's powered by my PC via USB so I can upload my code. From what I've been reading I have to connect one of the ground pins to the Xbox so they share the same ground, am I right?

Because I already tried to connect one of the LED pins to the analog pins on the Nano, but when I tried to read the value, I always get 0. This is probably because the Nano and Xbox didn't share the same ground. Since I'm new to all this I just wanted to try out this scenario by connecting an LED to the Nano and read the value from there, this time all of the RGB LEDs anodes gave me a value between 400 and 600, but they never changed. Am I right in the assumption, that this is because the LED is controlled via D9-11 pins with PWM, which is why they always get the same voltage?

I also wondered if I could get the info about the LED status (or rather the Xbox status) from somewhere on the lower levels via the digital pins on the Nano. But there aren't many schematics out there sadly.

Anyways, can someone point me in the right direction and explain what I'm doing wrong and why?
My knowledge is limited to what I learned from school, namely ohm's law and stacking together some simple circuits with LEDs but that's it, so I'd like to learn something.

2

Without seeing the drive circuits for the LEDs, one can only guess.

Assuming the LEDs are being switched high side through a resistor to a voltage source, you could use the anode pads as your activated indicators. With no load, that would be whatever supply voltage the Xbox uses. If that's 5V, then you can use the anode pads as digital inputs. If any of those assumptions are invalid, more information is required.

If you aren't using a galvanically isolated interface to your circuit (e.g. optocouplers), you must connect the grounds between the Arduino and Xbox. Voltages are typically referenced to ground. If you don't have a common ground, you can't use voltages referenced to ground between the two circuits.

I know this isn't an electronics website, but you should still use schematics when discussing circuits. That makes it less tedious to try to understand how things are connected. The process of drawing an intelligible schematic will require you to provide details that would answer many of the questions we might have.

3

OK the xbox and arduino absolutely need a common ground.

The diagram shows the leds are connected with a common ground.

When lit they will develop about 1.8V so you can read their status with digital pins on the arduino.

You may need to add resistors so that the voltage drops below about 0.7V when the signal to them is off.

4

Alright so I tried to create a "schematic" of the setup I tried here:

I've also tested this setup with an analog pin (A0) instead of D2, but neither gave me any valuable result.
The digital pin just randomly switched between high and low even though the green LED was constantly on and the analog pin just returned random numbers.

Could it be that I'm sharing the common ground wrongly? Sorry I'm a total noob, but I mean I need to connect it to my PC so I get the serial output to see if I'm reading anything, so this has to be the way, right? Or do I actually need an octocoupler with this test setup?
I also have two other Nanos, so I could technically connect Tx and Rx to one of those and read the values from there, at least if the ground sharing is actually the issue here.

Is there any good lecture for dummies I can read on basic electronics? I really feel like I haven't understood them yet after my failed attempts here.

5

shawly:
Alright so I tried to create a "schematic" of the setup I tried here:

I'd call that a cartoon. A schematic would show standard component symbols, not pictures of components.

This is a schematic of the relevant parts of your drawing:
xbox.jpg

I've also tested this setup with an analog pin (A0) instead of D2, but neither gave me any valuable result.
The digital pin just randomly switched between high and low even though the green LED was constantly on and the analog pin just returned random numbers.

I thought you were going to remove the Xbox LEDs. Why are you experimenting with it in place? The voltage levels will be different without an LED in the circuit.

Do you know how the Xbox LEDs are driven? Steady on? Multiplexed? PWM'ed?

Could it be that I'm sharing the common ground wrongly?

Looks right to me.

Is there any good lecture for dummies I can read on basic electronics?

I learned the old fashioned way - went to college. Electronics isn't something I'd want to learn on my own. You won't know what you don't know and if you don't have a good foundation, so many things can trip you up.

xbox.jpg

6

dl324:
I know this isn't an electronics website, but you should still use schematics when discussing circuits.

How very peculiar!

That appears to me to be the main thing discussed on this forum, entitled "General Electronics"! :astonished: How could we be so sorely misled? :roll_eyes:

Yes, well other things are indeed discussed from time to time. :grinning:

7

shawly, im trying to help. So why not give me some karma?

As far as I can see there is nothing wrong with your circuit. The led should show around 2V (a good logic 1) when on, and less than 0.7V (a good zero) when off.

you need to use a logic input pin and NOT input-pullup.

If you are seeing random 1s and 0s there are a few possibilities. Perhaps the green led is not continuouly lit, but flashing so fats it looks always on?

a small capacitor would smooth that out. Dont make life complicated, you should not need optocouplers etc.

Please show the code for your sketch.