Newbie question: circuit for harddrive indicator

For a first project, when you are a little uncertain about whether your project might damage something in the computer, how about this?

What if you used a light sensor, say a phototransistor, that would be illuminated by the light from your harddrive led? The phototransistor acts sort of like a switch, when the light is on it the switch is closed, no light and the switch opens. That can then be used to turn your transistor on and off. And the transistor can turn on and off enough power to switch your 3 uv leds on and off. All this could be tested without risking wiring it to your computer, so worry can be reduced, always a good thing with a first try at something.

Sound like a reasonable approach? Then wen can move on to the next step.

Nicely done.

I would check to see whether your choice of phototransistor can supply enough current to directly drive 4 UV leds or not. That was why I suggested using the phototransistor to drive the base of a separate transistor, giving more gain and more power, letting you adjust the bias on the transistor to make best use of the hard drive led intensity levels.

Another newbie here. I haven't dabbled in optoelectronics yet, so I thought I'd try my hand at this circuit...

Here's what I came up with. Anything wrong with this?

IDE LED +5V GND GND +12V GND + Red Black Black Yellow .-------. .---------------------. | o o | | o o o o | '-------' '---------------------' | | | | | | | +-------------------------. | | | | | | V ---> \| | UV | | - |---' LEDS | | | ---> |------+ | | | | 120 Ohm | '---' | | ___ // | '---------+--|___|------>|------+ | 120 Ohm | | ___ // | +--|___|------>|------+ | 120 Ohm | | ___ // | '--|___|------>|------' 240 Ohm New HD LED

(created by AACircuit v1.28.4 beta 13/12/04

Well, first uncertainty I don't know is, if the phototransistor base (if present) should be grounded if it's not used to force drive the transistor or left floating? (The only time I played with one, I left the base floating...)

The old HD LED is probably not enough to drive the phototransistor fully, so the resistors should probably be less than what if they were hooked to the +5V directly?

If the old HD LED was recycled to the "new" side, that LED+phototransistor could be replaced with an optoisolator. That should be a safe way to trasmit the signal (and essentially what that above is), but are there any others? I would be vary to directly drive a transistor base from mobo IDE LED output, since that would mean you'd have to hook the PSU common and mobo ground together, right? (Which I'm not sure would be a good idea, since they're so far apart from each other... Or even if they should be in same ground potential in the first place.)

Anything else I didn't think of?

You can use Pin 39 on the IDE connector to detect activity on the hard drive.

Simply connect it to a transistor driver and put the LEDs as loads. Let me know if you need help with the actual circuit.

Kunal

One pin of the HDD Activity header connects to +5V through a resistor, commonly 220R-330R. Other pin goes to pin39 of the IDE cable/drive which is an open-collector NPN transistor, switched on activity so that header pin goes low and the LED comes on. There are a couple of steering diodes so either drive will light the one LED.

You *can* use a PNP transistor switch and the molex supply to boost the current, but it's a lot safer to just plug an opto-isolator's diode in place of the LED; check its rating, you may need a small NPN transistor switch as well. If you put your 3 UV leds in series (with the appropriate resistor) the 12V supply will run them all with minimum wastage.

cpemma (et al):

I hate to do this to you, but could you draw the circuit with actual part numbers and values? I know that seems kind of lazy, but I haven't had any circuit or breadboard experience and an example would really help (although Toni's example was good after I printed it off from Notepad.)

I think I understand Don's, Toni's, Kunal's and your comments about using an optical device to isolate the harddrive activity signal (led drive) from a transistor that switches the 5V's current for safety's sake.

When I say I'm a noobie, I mean I am a nooooooobie!

Fob

Have a look at this one:

For a few leds, most any small NPN transistor will do, a BC107, BC109 or

You could also use a 5V supply, changing R1 to a 1k.