🚀 go-pugleaf

(I'm cross-posting this to pc.hardware for those tinkerers over there)

I've been an avid reader of Sci.electronics since my college days and it
has always been so helpful.  The wealth of information is staggering and
I'd just thought I'd submit this simple one evening project for those
interested.  It's really too simple to be considered a significant project
but I felt it was useful enough to make one myself half a year ago.

For those who have played with Compaq computers, you'll note that they
use interesting floppy drives whose in-use LED changes color depending on
the density of the floppy.  I thought this was pretty useful since I'm in
such a rush, I rarely pay attention to the floppy label and rely on the
LED color to determine the capacity.  I liked this feature so much on my
Compaq at work, I wanted to add it to my 386 at home.  So here's an ASCII
schematic of what I made:

                             +5 VDC
                                |  1/6           1/6
                               |\ LS04       |\ LS04
Reduced Write (pin 2)  >-------| >o----+-----| >o-----+
                               |/      |     |/       |        NOTE: red and
                                |      V              V        green LEDs are
                               Gnd     - Red          - Green  actually a
         ____________                  |              |        single bicolor
         Drive in Use  >----/\/\/------+--------------+        LED.
                           220 ohm
                                       Red = Lo Density   Green = Hi Density

                     Figure 1 - New In Use LED circuit

Notes: - Reduced Write (pin 2) is low when low density (360K/720K)
       - Reduced Write (pin 2) is high when high density (1.2M/1.44M)
       - Reduced Write is located on pin 2 of the 34 pin edge connector
       - Drive in Use on most floppy drives is active low and is connected
         DIRECTLY to the cathode of the original In-Use LED (see Fig. 2)
       - Power for +5 VDC can be obtained from pin 4 of the power connector
       - Ground can be obtained from pin 3 of the power connector
       - Most (if not *ALL*) bi-color LEDs have a common cathode
       - Tie all unused inverter inputs to +5 VDC or Gnd (ground)
       - You may not need the 220 ohm resistor if your floppy drive already
         has one ON THE CATHODE side.  Most drives however are configured as:

                            Red
                  220 ohm   LED       ____________
       +5 VDC >----/\/\/---->|------> Drive in Use (often NAND gate output)

             Figure 2 - Circuit often found on most floppy drives

I took a LS04 and snipped all the pins off leaving just the stubs on the
sides of the chip.  Soldered some long wire-wrap wire to it then wrapped
the chip in some duct tape.  Small enough to tuck somewhere on the floppy
drive itself.

Most of the parts can be found in your junk box or at Radio Shack.  I don't
know if they carry a bi-color LED though.  I was lucky since I had just
bought a Toshiba 1.2Mb floppy drive from SoftWarehouse (a fairly large
computer store chain around the USA).  This Toshiba had a bi-color LED
built-in!  But it was only there so the user could pick the LED color
with a jumper.... permanently!  A few cuts with an Xacto, some patch work
to the circuit and that was it.

I probably went overboard on the details, but what I appreciate about
Sci.electronics are the folks here who don't assume everyone is an
electronics wizard.  We all had to start at the bottom sometime and I
hope this little project will encourage other beginners to get their feet
wet.

Cheers!
Cliff Yamamoto
-------------------------------------------------------------------------------
USnail: Clifford K. Yamamoto - KA6JRG  | Email:  cyamamot@kilroy.jpl.nasa.gov
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