Friday, March 5, 2010

Chapter 4 - Exercise 20 Update 2

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.


  1. The best way to solder 2 wires inline is to have them perform the manly arm handshake. You know that weird one where 2 people grab each other's forearms


    I believe one of the US armed forces came up with this technique and documented it way back in the day. I don't recall which one and what they called it, bad memory. I'm sure a service person will show up and represent.

    I was shocked that I couldn't find this online, So I snapped a few pictures really quick until someone can find us the obvious Wikipedia article on it :P

    If one or more of your wires are stranded twist the strands together before you start like this:

    Pic of 2 stranded wires

    Next wrap the end of one wire around the other. you can see a pencil drawing below the wires of what we are eventually shooting for.

    Picture of first wire's end wrapped around second wire.

    Now just wrap the end of the other wire around the first. Its kind of like a arm-handshake :D

    The second wire's end wrapped around the first wire.

    Optionally if you get good at this technique you can also twist the "arm" section of the handshake. If you look closely at the last picture, this is what i have done.

    Now just apply solder, and if your like me curse yourself for forgetting to stick the heatshrink tubing on first! :D

    If you do this correctly it should be difficult to pull the wires apart before you even solder!

  2. Rather than going through the grief of soldering the 22 gauge pigtails to the stranded ribbon cable conductors, consider just tinning the 24 gauge ribbon cable ends. Once they are tinned, they are about the same diameter as 22 gauge solid wire and when tinned, plug into a breadboard just fine.

    I figured out that I can tin wire ends quickly by clamping my soldering iron in a vice and then bringing the solder and wire together to the iron. I keep a damp cloth close by. I push the wire and solder against the iron's tip. As soon as the solder flows into the wire, I drop the solder roll and quickly wipe the newly tinned wire clean of any excess solder to make a nice smooth wire end that will easily plug into a breadboard.

    I'm not quite to this activity yet, but looking ahead, I am preparing my keypad already by attaching the ribbon cable so I tinned both ends of the wires first.

    It's much easier to solder to the traces on the keypad if the wires are tinned, allowing me to bend, with my needle nose pliers, a little hook on each conductor at the keypad end, giving me a mechanical connection to hold everything still while I soldered it all up.