I realize this the millionth thread with fading LED in the subject line but... I'm about to start modding a new case (Antec Sonata, nothing big, just a few improvements.. ) and I'd really like the HDD led to fade in and out rather than just being on/off (looks more styligh IMHO). After reading these forums and browsing others I'm lead to believe that this can't be done by just putting a (big) cap in parallell with the HDD LED. So browsing on I stumbled across macroman's Knight Rider circuit and got the idea of using the LM4558-part of the circuit to give a fade. As it is now the circuit outputs around 8V and I'm using a res to cut it down to a suitable value for my LED, however I was thinking if there's a way to change the existing res's so that the output voltage would be about right and thus eliminating the need for the extra resistor. I don't much about electronics, but I've managed to figure out that R1 and R2 make up a voltage divider, but changing the values didn't change the output from pin 1 .. Ofcourse using and extra res isn't a big problem but if there's a way to avoid extra components/heat, I'd appreciate it.
Before anyone else replies ...or is there a better way to fade a LED in out? The simpler the better...
Sorry I don't have values, but analog circuits aren't my bag. Just for a guess, that would be a 10k pot for VR1, a medium value ceramic or electrolytic cap (probably 10-100 µf), VR2 would depend on the op amp (10k should work also) and for the op amp, I would think it would work with pretty much any non-inverting op amp. In that VR1 would control how long it takes for the LED to come on, VR2 would control the gain of the op amp, so it would affect both the fade on and fade off time. If someone better with analog circuits could help it would be apprecitated. EDIT: I wouldnt turn VR1 all the way up because you would short the HDD+ and HDD-, and the pins on your op-amp may vary from the diagram.
This would only work if the LED is switched on the - line, else it would ground out the input! And the opamp is wired so it acts as a Schmitt trigger, which would mean the LED would be on or off (back to the starting point!). EDIT: ZapWizard has a circuit at http://www.zapwizard.com/schematics/index.html .
The led is switched on the - input. Err, now I see that all that circuit would do is delay the LED until the until the cap is discharged enough. Bah. I hate analog stuff.
