how to listen volt output from PC?

[xanderhan]

hello every body...
I have some trouble with my project, I wish there're people can help me here....

let's to the point
I want to ask, How I can listen volt output from HHD led on PC...

my plan, I want to make my arduino can control my PC....
my arduino can switch power and restart.....
with listen HDD Led, so if led doesn't blink yet on 10 second arduino can restart that pc and switch power on...

I doesn't make the code yet, cause I'm confuse how to write that code..  :~
can anybody here help me make some basic code which can finish my project, I'm really stuck..  =(

thx for attention....
I'll wait for reply, and thx before.... 

[RIDDICK]

1.
u could use a photo diode and read it via an analog pin...
or u read the LED power line directly...
http://arduino.cc/en/Reference/AnalogRead

2.
instead of reading the HDD LED:
u could send the arduino a message every 5 seconds...
and when the arduino misses that message for 20 seconds, it "presses" the reset button...

3.
in order to "press" the reset button, u could use a relay...
if the arduino and the supervised box use the same power supply: u connect the reset-signal line directly to the arduino and pull it down (IIRC)...
http://arduino.cc/en/Reference/DigitalWrite

[pbrouwer]

Hi,

I take it you're trying to make a watchdog timer. I wouldn't use the HDD LED signal for that. First there might be a voltage issue (the signal probably isn't 5V), second hdd activity is not a good way of checking if a computer is stuck. A computer can run fine without HDD activity (for a while), and a computer that gets stuck during HDD activity may be blinking it HDD LED all the time.
Like the previous poster, I suggest you use a program that sends a heartbeat signal every now and then.
An easy way is to use the computers parallel port. It uses 5V signals (like the Arduino), and its fairly easy to program. If you use another port (if your computer doesn't have a parallel port), you can make an opto-coupler using an led, a photo-resistor and some black tape. That way you don't have to worry about voltage conversions etc. It also means you keep the electrical circuits separated, which might improve stability, and prevent accidental miswirings from frying your computer or arduino.
Using the built-in USB to serial converter may not be a good idea. It can be a bit "moody" every now and then, so you would reset a perfectly fine running computer.

Pieter