Classic Battery Terminals

[DanLewis]

I don't know why I didn't think of it before, but the solution was so simple!

A few years ago, I built a VHF antenna out of some PVC pipe and a tape measure. The tape measure elements work well because they are easily foldable and lightweight (and REAL easy to measure!).

I had some extra steel tape from this tape measure laying around, so I just cut a piece of it to size and voila, it works! The tape used in a garden variety tape measure is about the springiest stuff out there, and although it is very thin, it's still enough to handle the current drawn when pulling a card through the reader (about 300 mA).

I was able to solder the wire to the terminal even though it was made of steel. I think this particular type of steel takes to the rosin-core solder better than whatever that micro switch lever was made of.

Another interesting happening:

When I took the machine apart, the two wires that power the display had broken off from excessive bending.

When I soldered them back on, there must have been a poor solder joint on the black wire (the one closer to the bottom of the machine) because when I powered the calculator up before completely reassembling it, everything worked fine. BUT, when I tightened the screw in the upper right hand corner (underneath the corner of the card reader bridge board) the top row of LEDs would not light up, and the corner of the little tan box (I think it's a group of resistors?) that's soldered to the board behind the LEDs became very HOT!

I checked to make sure this only happened when I tightened that screw, and sure enough, that was the case. I reheated the black wire's solder joint, making sure to flow the solder more evenly onto the board, and everything is now ship-shape.