It's a Miracle!

[Winder]

Well, not really. Just bored. Dug out the old HP-28S after a nightmarish experience trying to use a non-RPN calculator as my garage abacus. These old double-door HPs were notorious for busting the battery cover due to a poor design resulting in 200 ft-lb of force on a half millimeter plastic tab (well, I don't know that for sure, but there's a lot of force there). Saw this online and decided to convert to button batteries from the N-type with a couple of "faux" batteries to take up space and reduce the outward pressure on the battery cover since mine is still intact and replacements are no longer available. Going to go have some Wild Turkey now to prep for Christmas.

[romberg]

The 28s I used in college (30ish years ago or so) is still sitting on my workbench and used to bias every amp I have. I am barely able
to use any non-RPN calculators. My computers all run emulators that run HP firmware from the old calculators. Math just flows more
smoothly with a stack and postfix notation. My brain just trips all over itself without them.

The N cells do seem to last me a very long time. But I'm intrigued by your button battery conversion. At this point I think there is a chance
my old 28s may outlive me. And I'd hate to have the battery door breaking through a wrench into this plan. I'd be very interested in a few more details
on what is involved in this conversion. What type of button cells? How many? How did you construct the faux batteries?

Mike

[Winder]

I hear you. I have a 48G emulator on my iPad, use a 48GX at work, keep a 48G where I wind pickups and a 15C here next to the computer. I wanted a garage calculator for woodworking and other projects and loaded up an old Sharp calculator I bought only because it does various unusual calculations useful for coding (HEX, OCTAL, etc.). Used it for one class in college in '89 and then put it away. The 28S and 28C suffer from excessive stress from the cover due to the N-Types under spring pressure. There's not a lot of "meat" to keep the cover in place. Mine isn't broken, but it's a bit dicey. This allows you to dramatically reduce and control that pressure, which is cool. I'll have to admit, I stole the idea from here:

http://www.mpshp.com/hp28s/

If it comes to it, I can fashion the fancy steel cover too. I used 3 each LR44 batteries - didn't put a lot of thought into that part.

Measured the depth of the cavities to determine lengths and matched the relative diameter of an N-Type battery. The LR44 buttons are pretty much that diameter too. I made the bigger "battery" out of cardboard (toilet paper roll ), rolled it tight and then wrapped it in aluminum foil that extends past the ends of the roll a bit and secured with masking tape. Fold the foil on each end to make "battery" ends (hemispherical, basically). The smaller one is pretty much just foil that is a bit smaller than a button battery so it doesn't get stuck in the calculator. I dropped the three buttons in the shorter cavity and put the foil button on top of them. Maybe next time you need batteries you can go this route. I think the buttons are cheapr too.

The 28S was a workhorse for me for many years. Nice to have it back in action.

[Reeltarded]

You are a supernerd, a real one, not just some whore in snapchat with fake glasses!

[Winder]

I would argue, but it's probably true.

[pompeiisneaks]

Heh I started in Civil Engineering before moving to computer work, and had an HP48G for a while and then went to a 48S I believe. Love those RPN Monsters! I still have mine around here somewhere. I also once installed an app for my android phone that was an hp48 emulator. Loved that too

~Phil