HP-25C Eumulator

[pbnelson]

I got a great case on eBay for a few bucks and just had to share. First off, go to eBay and search for "5Pcs Plastic Electronic Project Box Enclosure Instrument Case 100x60x25mm SM". I managed to get five! cases for under four dollars with shipping, and they only took two weeks to arrive from Hong Kong.

I got the overlays from "walter b" in this forum (http://www.hpmuseum.org/forum/post-29895.html) and include them for convenience. Note I had to print Walter's overlays at scale 106% on my Epson inkjet.

I made my own quickref guide (pdf attached).

The calculator buttons work right through the overlay paper! There is no need to cut little holes for each button. The buttons are properly engaged right through the paper, with no errors, ever. In fact I printed those on #100lb card stock, and covered them in librarians tape (thicker than packing tape). They are essentially laminated, very thick and sturdy. I used a ruler and an exacto knife to cut out the precise holes for the capacitors and bubble display. I just lay them atop the keys and press. They work perfectly.

The case cutouts I made with a Dremel tool. It cut through the plastic like butter.

The power switch on the circuit board is a critical weak point. I had already broken the original and substituted a sturdier one, but even that still felt delicate. In the end it made more sense to relocate the switch off the circuit board altogether, and use a big one. I've been waiting for the right project for that toggle-switch for 15 years!

For full sized pictures go to my Flickr Album

















edit: replaced duplicate image with topside view