On my new case I want to make the HDD indicator a VU meter like this (or similar). I am wanting while idle for the needle to "wander" at around 1/3 scale approx (not sit stationary) then peak into the red when HDD activity is present. How "flat" is the DC comming from the PSU or am I going to introduce some sort of circuit to give me the desired effect? I have some basic electronics knowledge and can build what I need - I just don't have the know how to come up with the solution.
I have been giving some thought to my dillema.... Would a circuit designed to flash random LEDs (addapted to my needs) do the trick? Instead of having the LEDs, have resistors of different (but close) values all connecting up to the meter. This would then give the effect of having a random (within parameters) voltage applied to meter - giving me the ripple effect I want Next question...... If I am on the right track, does anyone know where such a circuit/circuit design may exist?
i dont see a problem with using a vu meter. to get it to 'idle' at about 1/3rd scale you just need to bias it (ie. from a resistor and the 5V rail). then add the signal from the IDE led header on mobo (through a diode and another resistor). You'd may want to use presets or variable resistors but make sure you don't short circuit either input or you'll bust motherboard or psu. most meters give an indication of 'full scale deflection' current (640uA or something in the one you linked to). I wouldn't use a meter with more than 20mA FSD if you can (this is a similar current to what the LED would draw).
Sweet. It sounds like this mod could be easier than anticipated. How do I find out how stable my PSU is? The label just lists total power and max output (volts and amps). What sort of fluctuations in output are common?
The outputs on the PSU only fluctuate +-20 mV if memory serves correctly. Not really enough to give the desired effect. You could take a DC line, put on a cap to block the DC componet, and feed the AC componet (noise) into a op-amp, but I wouldn't expect that to vary in level a lot. A random noise generator may be the ticket. Maybe throw in your sound-card's output into the mix so when you have a song going that influences it a little bit.
