Derek Walker continues the know-how on a new hardware device to allow
two printers to be connected to your Electron

To follow on from part one, I now give details on how to build the Printer Switch. Firstly, you need to dump the scrolling screen PCB figs to a printer [See the articles on Saving Memory Direct in EUG #1 if you're unsure about this first step - Will] or, if you have no access to a printer, write to EUG for a copy of the original design on A5 paper.

Fig. 2 shows the underside of the PCB which can be copied onto copper-clad board and etched. Note that all dashed lines are links. Once the board is etched and drilled, it can be populated with the component overlay (fig 1).

Follow the steps below:

1. Using the solid wire, cut to length and bend all the wire links. To make the job neat, first, take a length of wire off the reel and stretch it a little to remove all the kinks
2. Solder the links onto the board
3. Insert and solder resistors R1 to R6
4. Insert and solder the two 26way headers into positions SK1 and SK2
5. Insert and solder the 36way centronics connector into position SK3
6. Insert and solder capacitor C1 - check its polarity in fig 1
7. Insert and solder integrated circuits U1, U2 and U3. Again, check orientation
8. Lastly wire the switch S1. Before wiring the switch, check the switch is in its most anti-clockwise position and then remove the control nut and lockwasher. With a small screwdriver, remove the small metal collar and place it back in the position labelled "2". This will restrict the movement of the switch to just two positions. Cut three lengths of wire approximately 150mm long, bear the ends and solder one wire on each of the three terminals A, 1 and 2 of the switch. Now solder the unterminated ends on to the board. The positions are shown in the overlay.

Check all the links and resistors are in the correct positions, the capacitor is the correct way round and that U1 and U2 are HCT245s, U3 is an HCT244 and they are soldered in the correct orientation. Finally, check for solder splashes on the underside of the board.

The big moment has arrived - it is time to plug it in. Connect the unit as described in part 1, set the switch to printer one and start printing!

Derek Walker, EUG #6