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How do the buttons on a calculator work?

My calculator has these black lines (under all the buttons) that are very close but not touching in wavy designs right on the PCB. How do these buttons work? Is there a way I hook up a SMT push button to this?

Like I mentioned before, both my calculators have these black traces. Is this a covering over the copper? How would I get to the actual copper? Do I try to sand off the black? 

Thanks!

iceng4 years ago
The button has a conductive rubber n the bottom
which when pressed down short those wavy lines
and activates the calculator electronics.

There should be an underlining copper conductor BUT
it may be way too thin to survive and support your SMT push
button soldering even with tin lead solder.

However,  you may be a superman at soldering and make it work.

A

HavocRC (author)  iceng4 years ago
Well, I guess I didn't make myself clear enough. I'm not going to actually put a SMT switch directly to the board, I just need too hook up the wires to the board and then run two wires to my switch that would act as a calculator function. I tried scratching off the black, I didn't really see any copper; is the copper that thin? I'm I scraping it off? Can I just take a piece of sand paper across the whole board?

Thanks iceng!
iceng HavocRC4 years ago
I haven't taken an electronic keypad apart recently and can't be 
sure what cheap low-cost  innovations are being done these days.

They could be running a carbon tract right into that infamous
Chinese epoxy black passivisation blob.

Sand paper is too rough, it may remove the copper traces all together.
  • Try the thin flat  fiber dish scrubber  pads they are great at cleaning up a copper board.
  • Then, if that is too soft,  try steel wool.
  • Finally try a hobby knife with a curved blade
  • Scratch & nibble at the end of a wavy line to expose what is underneath.



HavocRC (author)  iceng4 years ago
Ok thanks iceng I will try that soon. I'll tell you what happens :D