Let me tell you - soldering up the keypad with the ribbon cable is tedious... frustrating... nerve-wracking... and somewhat fun. It looks very Frankenstein-ish and my multimeter tells me all the wires survived the soldering... one or two slight singes as I was putting on shrink wrap, but if I find a wire is bad, I can always make that one of the un-used code numbers, right?

The hard part (for me, at least) is soldering a 22 gauge solid core wire to a 24 gauge stranded wire... hard to make them stay together. Anyone have any suggestions?

Since I'm not going to cut into my wife's PC tower, I think I've come up with a possible variation of this, suggested by the author's text. I think it might be fun to build a box for my son that uses a combination of Exercise 20 and maybe Exercise 11. I could build a noise maker circuit and have it triggered if the code isn't entered properly... or maybe implement the magnetic switches for the alarm system into the box... if the lid is opened without the proper code, the magnetic switch is broken and the alarm sounds. I'll have to think about that...

So, while I wait for my replacement dual coil relay, I'll start wiring up the breadboard for testing...

Also, I had to hunt down the Panasonic DS2E-SL2-DC5V data sheet to understand what's going on inside... here's a link in case you're interested. Page 6 is what you're looking for, DS (2 Form C). I'm still trying to figure out how this thing works, so please chime in if you have an explanation... the more the merrier.

UPDATE: I just created a small circuit with a single LED - I plugged in the wire for pin1 (COM) to positive voltage... and connected the the LED to negative voltage. I then stuck each wire (except for pin 2 which doesn't have a function) into the positive side of the LED, pressed its corresponding button, and hoped it lit up. It lit up for each and every wire. So my soldering worked and the keypad works as desired. That made me happy. Video added below.