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-- Hard Disk Drive Utilization Meters
-- Category: Guide
-- Posted by: Marsupial
-- Posted on: 2003-03-05
-- Price: ~ $NA USD
-- Pages: 1 2 [ 3 ] 4 5
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Ok, a needle might be good looking, but everything in my box is digital, so a digital version of the HDD meter was needed.

   What we'll do is place a led-array meter using a LM3914, a 10-led voltage indicator. The HDD led indicator always draws the same current and voltage, but since it pulses with more or less speed, we will tweak it to "charge" and "discharge" slowly. We will do this with a capacitor. its charging and discharging values will be adjusted with a resistor giving it "feedback". This setup is known as a RC filter and is normally used to regularize (remove peeks) in a power circuit.

   We will use it only to ensure that the LM-3914 will have a nice reaction time: when inactive, the voltage will be 0. When there is a low rate of HDD usage, the HDD led would flashs slowly. The capacitor will charge and discharge leaving only a low voltage to the LM3914. Upon larger HDD usage the capacitor wont have time to discharge and will lead a direct voltage to the LM3914 for a full span indication.

   There are a few problems with this setup. The RC filter has a feedback effect you might not want to send to your motherboard, and the LM3914 might suck a little too much juice. That's where an optocoupler is handy. The optocoupler will act like a switch, but this switch will be activated by an integrated led on the chip. This led will be plugged on the mobo's HDD led indicator, and the switching action will activate the RC filter for the LM3914 to get the spanned values.

   What's needed to build it:

  • Capacitor 220uF (microFarads) 25V

  • Resistor 330 ohm

  • Resistor 470 ohm

  • Resistor 3300 ohm

  • Resistor 10000 ohm

  • 10 Leds (3.5 volts forward voltage)

  • LM3914 (Led bargraph driver chip)

  • 4N25 (Optoisolator: 4N26 or 4N28 or TIL111 should also work)

  • 18 pin IC socket (to avoid soldering directly the LM3914)

  • 6 pin IC socket (to avoid soldering directly the optocoupler)

  • Perfed board (to solder the components on)

  • Wires

  • Molex connector (or another way to get 5V from your PSU)

  • Connector to your HDD indicator header

  • Jumper and jumper header (for mode selection - not mandatory)

  • 2*10-pin (optionnal)

  • Flatcable (IDE or the like - optionnal)

   Tools needed:

  • Soldering iron

  • External power supply (for testing)

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