Bulding an RPN Calculator

[pcardoso73]

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

[jackrubin]

Yes, of course - more please!

[Carsen]

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!

[Paul Dale]

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

[BobVA]

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

[Eddie W. Shore]

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

Eddie

[toml_12953]

(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?

[pcardoso73]

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