ledclock.txt

A tutorial on RT-Linux

Copyright (c) 2000 Lineo Inc, Release under the GPL
-------------------------------------------------

How to build and run your Fantazien display from real-time Linux
================================================================

By: Stuart Hughes, [e-mail], Sept 19th 2000

Revision: Phil Wilshire [e-mail] , Oct 12, 2000
          - moved sensor to pin 13.

Revision: Alan Hilton [e-mail] , 31 Jan 2001
	  - lxrt section included.

What you will need
------------------

o A standard parallel printer cable (I used the $14 radioshack cable).

o A good quality (temperature controlled soldering iron)

o A continuity tester (e.g a digital multi-meter)


Hacking the hardware
----------------------

o Disconnect the unit from the mains, and remove any batteries.

o Make a mark on the back of the case on the left hand side, half an 
  inch from the bottom and side of the case (you will drill into this
  later).

o Open your unit by undoing the 2 screws under the base (one is obscured
  by the sticker).

o With care pull the unit apart.

o Very carefully remove the large 40 pin dual-in-line chip that controls the
  unit.  Remember the chip orientation for when you replace it.

o Lift pins 1 to 8 of the 40 pin chip.  Pin 1 is on the bottom left near the
  end that has the notch looking at it from the top.

o Replace the chip in its socket.

o Cut the centronics connector off the end of the printer cable

o Drill a hole in the case where you marked it earlier, just large 
  enough for the cable to pass through

o Pass the cable through from the outside to the inside of the case.

o Strip back the outer cable shielding to expose 6 inches of the cable strands.

o Strip back each strand by 1/8th of an inch.

o Buzz out the connections from the 25 way D connector pins to the
  conductor stands.  The cable I used had the following colour coding,
  your milage may vary.  Here's what I found for my cable:

  D pin	  colour		Chip connection
  ---     ------		---------------
  2	  yellow			1
  3	  blue			2
  4	  orange+white		3
  5	  black			4
  6	  black+white		5
  7       grey			6
  8	  white			7
  9	  yellow+black		8

  10	  blue+white		13
 
  19	  red+white			ground (negative) large battery pad
  20	  green+white		ground (negative) large battery pad


o Following the guide above, carefully solder led connections to the 
  non-component side of the 40 pin chip socket.  Make sure not to
  short out any pads or adjacent connections

o Solder (D connector pin 10) the sync wire to pin 13 on the 40 pin
  chip on the same side as the other connections.

o Connect the 2 ground wires to the negative large battery connection.
  This location will be on the lower left hand side of the battery
  connectors with the thin track going up towards the wand.


o Re-assemble the unit, taking care not to trap any wires or obstruct
  the free movement of the display spring.

[Software instructions deleted, as they don't apply to this tutorial]