         Preparing the board layout
         --------------------------
         
         The board layout is supplied as PCL file of 300 DPI
         resolution. PCL files can be printed by HP Laserjet compatible
         printers. Type something like COPY PCB.PCL LPT1 /B at the
         DOS prompt to print the layout.
              The next step is copying the layout to a foil as used for
         an overhead projector. You can do that easily in the copy shop
         at the next corner, but make sure that
         
         - the black areas of the copy are quite dark
         - the lines are not interrupted
         - the copy is exactly the same size as the original printout
         - there is only very little 'dirt' on the copy
         
         If occasionally two lines are connected by 'dirt', you can
         remove these connections with a knife once you've etched it to
         a copper board.
         
         Note:
         
         If you don't have access to a Laserjet printer, you may try to
         print the PCB.PCX file also supplied with this package. Remember
         that it is a 300x300 DPI file.
         
         Sorry that no HPGL file is supplied. We used a pixel based
         program to draw the board layout.
         
         
         Etching
         -------
         
         Etching is not as complicated as you may think after you read
         this decsription. If you and your friends plan to build more
         than one interface, etching clearly is the technique of choi-
         ce.
         
         To etch a printed circuit, you need:
         
         - a UV lamp (a sun-ray lamp is fine)
         - a piece of perspex at least the size of the board
         - a single sided board with a photo sensitive layer
         - a thermometer (0 to 100C)
         - two bowls for devolping and etching
         - the developer (sodium hydroxide (NaOH))
         - the corrosive (sodium peroxydisulfate (Na2S2O8))
         
         Sodium peroxydisulfate (white crystal powder) is the corrosive
         we recommend because it is transparent so you can see what is
         happening to the board during the etching process. Don't use
         Iron(III)chloride (little yellow balls), another common cor-
         rosive. It is inferior because it's not really transparent and
         easily soils everything in range.
         
         Sodium hydroxide (white pellets), the developer, should be
         kept in a securely closed container as it's corrosive, too.
         


         Exposure
         --------
         
         The photographic layer of the board is UV sensitive (if you
         don't have a UV lamp, you can expose it to the sunlight for
         some hours). However, for regular exposure you should keep out
         sunlight and switch off neon lights.
              Remove the protective cover from the board and place the
         board on a plain surface. Now put the foil with the printed
         circuit on the board, align the edges and use the perspex to
         ensure it lies absolutely flat. The copyright notice should be
         readable now. Don't use a sheet of glass as glass blocks the
         UV rays. The distance to the lamp should be not less than 30cm
         depending on the power of the lamp. If it is too close, the
         heat may damage the perspex.
              To determine exposure time, you should try this first
         with a very small piece of the board (you should have it
         anyway, as the interface is not of a standard size). A 300W
         sun-ray lamp needs about 5 minutes, but this may vary, so you
         have to make some experiments with small splinters of the
         board. If the time is right, you will notice a slight change
         of color in the exposed areas. It should be possible to recog-
         nize the lines of the printed circuit now.
         
         
         Development
         -----------
         
         Prepare a solution of 10g/l sodium hydroxide in water, i.e. if
         you use 200 ml water you solve 2g of sodium hydroxide in it.
         If you don't have a balance of the necessary precision, buy
         the sodium hydroxide at a chemist's who prepares the solution
         for you. Drop the exposed board in the solution and wait until
         the circuit is clearly distuingishable and all areas that are
         to be etched away are shining copper. Light gray is not
         enough. That should take 2 to 5 minutes. If it takes longer
         than 10 minutes, something went wrong - try to increase the
         exposure time. Rinse the board with clean water before
         etching.
         
         
         Etching
         -------
         
         The corrosive solution needs about 500g/l sodium peroxydisul-
         fate. During the etching process, the temperature of the cor-
         rosive should be 50C to 60C. This can be assured by putting
         it over a pot filled with boiling water. 
              You have rinsed the board with clean water? OK, then you
         can put it into the corrosive. The etching process is finished
         when all areas that are to be etched away are deprived of cop-
         per. This should take no longer than 15 minutes. (If the
         temperature drops below 50C, etching is slowed down to a
         stop.) 
         
         
         Drilling
         --------
         
         Drill 0.8mm holes for the chip sockets and 1mm holes for ever-
         ything else. The joystick connectors are fixed with M3 screws,
         so you should drill 3mm holes for them. The cross hairs indi-
         cate the screw position for a special brand of connectors, so
         perhaps the connectors you purchased need the holes drilled at
         a different position.
