Having constructed the matrix panel itís no use without pins! These can be made using cheap plastic-bodied 2.5mm jackplugs which are widely available. We need rather slim 2.5mm plugs if they are to fit snuggly together on the panel. All the commercial plugs I found had quite large bodies and so two of them cannot be plugged into consequtive holes on the matrix. (Though I did use them for testing purposes).So I decided that I would try to make some slimmer plugs by modifying the commercially available ones. The plug body needs to be slim enough so that two can be placed together in consequtive holes but at the same time has to accommodate a resistor which is soldered across the two poles of the jack plug. The job is not so difficult but it requires patience and some machining. I donít own a lathe..but I have a drill press..which for the light machining we need here works fine. Simply insert the plug into the jaws of the drill and use a chisel as a machine tool. Those people with access to small modelling lathes etc will find the job even easier.
I have illustrated the steps needed to convert the jackplugs to the final pin for our patchpanel below. I think starting from scratch
It takes about 20 mins to make a complete pin.
Figure 1: First take an ordinary mono 2.5mm
jackplug and remove the plastic barrel
Figure 2: Now carefully pull off the tip with
Pliers, taking care not to damage it. You can
then dismantle the plug as in Fig 2. Melt a little
solder on the flat end of the central pin.
Figure 3: Now dismantle another jack plug and using
the tiny black insulating washer from that , reconstruct
a new plug as in fig 3, using the tip, base and central pole.
Figure 4: Now machine the base of the plug to a
diammeter of approx 3mm. as in Fig 4
Figure 5: File the flat end of the central pin to
a D-shape and then file (or drill ) a notch in the
base, so that it can accept one of the resistor leads.
Figure 6: Finally to make the body of
the pin, I machined some 5mm stock
plastic rod, and drilled a central hole
which forms a tight fit for the plug+resistor
Figure 7: You can use different coloured plastic stock for different
size resistors. I could only get hold of black or white, so
spray painting the top of the plug is another way of colour coding.