What is the voltage coming out from mobo for hdd led? Can I use some arrya of leds on that power source?
It's originally 5V but it's already been current-limited by an on-board resistor and through a few steering diodes and transistor switches. At the end of the day the average case LED sees about 8mA. It's easiest to swap the existing HDD LED for an optoisolator diode and use its optotransistor to switch your array, running the array from a 5V or 12V molex.
I might be missing something here... but i think that opto isolators only offer protection if you are using a higher voltage supply to drive the load such as leds, compared to just using a cheaper transistor & resistor, which also allows a higher load compared to the opto isolator. So if driving a heap of leds or whatever from 12v, then yes, use an opto isolator, but... if the opto is just driving a couple of leds from 5v, it wouldn't offer any protection over just using a transistor and resistor - the hdd led output is also attached to 5v via a resistor, so even if the transistor shorts, there's no difference, correct? Or am i missing something here
You can use the cheapo transistor and providing you make no mistakes you won't fry your motherboard. But it's far safer for the n00b to connect the optoisolator diode in place of the case LED, and take it from there.
hmmm... ok.. thanks for this precise explanation, but you lost me after two words: "fry" and "motherboard"... I think I'm just gonna skip my idea of blinking 16leds behind the SSD. I have no more budget to play with and buy another mobo in case of sth goes wrong But now when I got specialists attention - can I ask sth else? I soldered 6 red leds with 1ohm resistor - that was suggested by led calc. 6 leds, red, 2V, 20mA, 12V cable from PSU. They were beautiful for about 4 minutes, then stopped working I'm not sure if I saw them all going off slowly.. it looked like they were .. like the eye of dying terminator What happened? is it one of leds died? resistor issue? Calc suggested using 1/4W resistors, but I had 0.6W - does it make a difference?
A bug in the calculator. Use no more than five 2V LEDS on 12V, 100R resistor. The 1R resistor can't cope with voltage variation on the supply or variations in the LEDS.
I knew it! That is dissapointing.... ok, thanks, so 5 leds and 100ohm res... then when I use 6 leds then 5 with 100ohm and one led with 560ohm.. right? and how about W - 0.6W is this o for any combinations of 2V leds from 1 to 5?
Or two strings of 3, each string with 300R (or 330R). The calculator is OK until total forward voltage = supply, then it says 1 ohm for any current.
300 or 330 you said - does it matter? Cause I have 300ohm res but not 330 as calc says... less resist, more bright leds, is this correct? and that 0.6W is also ok?
300R is the correct calculated value (6V/.02A), 330R is rounded off to the more commonly-available resistors. Resistor heat = 0.12W so 0.6W is plenty of headroom.
I have a last question - How can I check how many leds i can plug into one 12v PSU power cable? I mean I have few rows of leds - one is 12 leds, 2x 4 leds and one 6 leds. Can I solder all cables and make one power plug for all and connect it to one power cable from psu? I want to use switches for each row of leds but all of them to connect to one power cable...
For a 14 gauge standard 4 pin molex connector the limit is between 500 and 1000 sets of series LEDs. BTW, you should be able to run all 6 red LEDs in series with a 100 ohm resistor and 12v just fine. You don't NEED to run the LEDs at their maximum forward current, and red LEDs will glow down to 1/2 mA or so
