HP Forums

Dear all,

As all of us, I am an RPN and hp calculator lover. My day to day calculator is an HP 48G, but now I need something larger with big keys (aging vision problems, so big keys = big letters and numbers).
After searching a bit, I could not find a big RPN calculator. So, in order to get a big, inexpensive RPN calculator, I would have to build one. Cool !
I started by looking for the perfect calculator. It must be thick enough to fit hardware inside and large enough so could have big keys.
I ended up and buying a 5£ desktop calculator off eBay. The idea was to strip everything inside, replace the original LCD by a two-line LCD and control everything with an Arduino. :-)
In the beginning I thought that I would touch only the LCD (single line and 12 digit and I needed two lines) and keep all the rest, but things didn't go that way.
The keyboard is a simple membrane keyboard. Unfortunately, the acetate sheet that has the tracks painted is glued to a pcb (not soldered), so it is not reusable. When trying to remove it, it became unusable.
Because of this I made a PCB for the membrane keyboard and it works! :-)

Until now, these are the materials used for this project:
1 Desktop calculator
1 LCD 24 x 2 display
1 Arduino nano
1 Custom PCB
1 battery (to be decided, but I might use a single cell powerbank).
and lots of wires

At this point the calculator is not yet assembled, but the arduino, keyboard and lcd are working.
If you like, I can give your more details as the project progresses.
I hope this post wasn’t too boring. ?
Best regards,
Pedro

Yes, of course - more please!

Yeah. This is rather cool! I would love to hear more, especially with what you are going to do with the keyboard layout. And...

Welcome to the Museum!

Nice project.

Are switches a possibility? The tactile feedback is worth a lot (to me).

I worked with someone who soldered one of those flex sheets to fix an HP 30B of mine. I'd have ended up with a blob of plastic (if I managed to avoid vapourising it).

Have fun with the software!

Pauli

Brilliant and welcome aboard! Yes, please do keep us posted.

Not at all Pedro, in fact, quite the opposite. Please keep posting progress on your RPN calculator. Wishing you much success!

Eddie

(03-23-2019 12:51 AM)pcardoso73 Wrote: [ -> ]At this point the calculator is not yet assembled, but the arduino, keyboard and lcd are working.
If you like, I can give your more details as the project progresses.
I hope this post wasn’t too boring. ?
Best regards,
Pedro

More details, please! Also, does that = key work as ENTER now?

Hi,
Thank you all for your kind words.

Quote:Also, does that = key work as ENTER now?

Actually the key which will be the ENTER is the big + key. I thought that the ENTER should be large, hence the choice.

Regarding the development, nothing happened this week. Today I received a hot glue gun and a set of metal files. I have ordered the files since the calculator's case doesn't close where the LCD is. Fortunately, it has some slots that can be filed down.

Then I will use hot glue to put everything in its proper place.

But before closing the calculator, I will have another problem to solve:

• the type of battery
• how to connect it
• single or dual power?
• do I use the coin cell that came with the calculator ?
  

The last reminds bullet makes me laugh, because it reminds me when I opened the calculator for the first time. Despite saying that the calculator is dual powered, the solar cell is fake and instead, they put inside a coin cell. :-)

Soon I will post some more photos and details.
Thanks.

Cheers,
Pedro