HP-25C Eumulator

[Thomas Okken]

(04-20-2017 05:06 PM)Gerson W. Barbosa Wrote:  

(04-20-2017 04:03 AM)nsg Wrote:  I thought it would not matter, but it seriously bothers me that registers are not preserved.

I don't care much about the registers, but I'd like the display mode being kept. Is it preserved on the real HP-25C?

Nice overlays! Colors are really important.

I should remember this, because I used to own one of those. That was a long time ago, though...
The 25C seemed a bit arbitrary about what it preserved and what it didn't. It preserved program memory and the 8 storage registers, but not the stack. I seem to remember that it did remember the LASTx register, and not the display mode... If you have the HP Museum CD set, look for "Getting The Most From Continuous Memory," that was an addendum that was included with the 25C, in addition to the regular 25 manual.

[rprosperi]

(04-20-2017 05:06 PM)Gerson W. Barbosa Wrote:  ...but I'd like the display mode being kept. Is it preserved on the real HP-25C?

No, after power-off/power-on, the 25C comes up in FIX 2 mode.

I suppose the thinking was that if you shut it off you are most likely done with your current problem, and then when going back to the 25C for the next problem, you may (or even likely will) prefer to use different display settings.

Since the 25C was derived from the existing 25 f/w, they no doubt didn't want to have to change the display logic settings to add storage into NVR, so would have come up with some logic like the above to explain why it's not saved.

[PANAMATIK]

(04-20-2017 06:18 PM)rprosperi Wrote:  No, after power-off/power-on, the 25C comes up in FIX 2 mode.

I suppose the thinking was that if you shut it off you are most likely done with your current problem, and then when going back to the 25C for the next problem, you may (or even likely will) prefer to use different display settings.

Since the 25C was derived from the existing 25 f/w, they no doubt didn't want to have to change the display logic settings to add storage into NVR, so would have come up with some logic like the above to explain why it's not saved.

Correct! The transition from HP-25 to HP-25C by HP was ingenious and made a very fast time to market possible at these competitive days. The firmware remained bit by bit identical, even the "Clear Memory" instruction, which cleared the external RAM chips at initialization, was left in place. There were only two hardware changes made: the two PMOS RAM chips were replaced by two pin compatible CMOS RAMs, and battery plus was connected to a previously unused pin of these RAMs. As the PMOS RAM chips itself (and not the ACT processor) decoded and performed the "Clear Memory" instruction, the CMOS RAMs decode unit was modified and just didn't execute this instruction.

The HP-25 firmware used the two RAMs (each containing 56 bytes) for storing 49 program steps plus 8 registers and the LastX register, 49+9*7=2'56=112 bytes, and placed the stack and display format inside the ACT chips volatile memory, the HP-25C consequently could not save the stack and display format after power off, because only the external CMOS RAMs were made non volatile.

I may allow to mention: The HP-25E since Rev 1.10 newACT replacement (HP-25 repair kit) also saves the stack registers and display format together with up to 111 programs and 88 registers in nonvolatile memory, and keeps their state and data even when batteries are removed.

Bernhard

[Thomas Okken]

(04-20-2017 07:02 PM)PANAMATIK Wrote:  The transition from HP-25 to HP-25C by HP was ingenious and made a very fast time to market possible at these competitive days. The firmware remained bit by bit identical, even the "Clear Memory" instruction, which cleared the external RAM chips at initialization, was left in place. There were only two hardware changes made: the two NMOS RAM chips were replaced by two pin compatible CMOS RAMs, and battery plus was connected to a previously unused pin of these RAMs. As the NMOS RAM chips itself (and not the ACT processor) decoded and performed the "Clear Memory" instruction, the CMOS RAMs decode unit was modified and just didn't execute this instruction.

But then how did the RAMs get cleared on cold start?

[rprosperi]

(04-20-2017 07:02 PM)PANAMATIK Wrote:  The transition from HP-25 to HP-25C by HP was ingenious and made a very fast time to market possible at these competitive days. The firmware remained bit by bit identical, even the "Clear Memory" instruction, which cleared the external RAM chips at initialization, was left in place. There were only two hardware changes made: the two NMOS RAM chips were replaced by two pin compatible CMOS RAMs, and battery plus was connected to a previously unused pin of these RAMs. As the NMOS RAM chips itself (and not the ACT processor) decoded and performed the "Clear Memory" instruction, the CMOS RAMs decode unit was modified and just didn't execute this instruction.

The HP-25 firmware used the two RAMs (each containing 56 bytes) for storing 49 program steps plus 8 registers and the LastX register, 49+9*7=2'56=112 bytes, and placed the stack and display format inside the ACT chips volatile memory, the HP-25C consequently could not save the stack and display format after power off, because only the external CMOS RAMs were made non volatile.

I may allow to mention: The HP-25E since Rev 1.10 newACT replacement (HP-25 repair kit) also saves the stack registers and display format together with up to 111 programs and 88 registers in nonvolatile memory, and keeps their state and data even when batteries are removed.

Thanks for explaining that Bernhard, I have wondered why the items preserved isn't simply 'everything'. It never occurred to me they could have created the 25C from the 25 with no f/w changes, only h/w. And let's face it, they did get all the really important stuff. Ingenious indeed!

[Gerson W. Barbosa]

Thank you all for the valuable information. I've noticed the production years coincided with my high-school years (1976 through 1978). I wish I had one back then, no problem the default FIX 2 display, instead of our 7-place logarithm tables.

[PANAMATIK]

(04-20-2017 10:24 PM)Thomas Okken Wrote:  

(04-20-2017 07:02 PM)PANAMATIK Wrote:  The transition from HP-25 to HP-25C by HP was ingenious and made a very fast time to market possible at these competitive days. The firmware remained bit by bit identical, even the "Clear Memory" instruction, which cleared the external RAM chips at initialization, was left in place. There were only two hardware changes made: the two PMOS RAM chips were replaced by two pin compatible CMOS RAMs, and battery plus was connected to a previously unused pin of these RAMs. As the PMOS RAM chips itself (and not the ACT processor) decoded and performed the "Clear Memory" instruction, the CMOS RAMs decode unit was modified and just didn't execute this instruction.

But then how did the RAMs get cleared on cold start?

Good question! The HP-25C firmware does not check the RAM contents at cold start and there is no checksum test. Therefore it does not display "Error" like the HP-29C does when RAM contents is lost, because the more advanced HP-29C firmware reads a RAM check word and clears the RAM if it is not correct.

I assume that there could be a hardware "Clear Memory" inside the HP-25C CMOS RAMs at power up, that resets all RAM bits to zero, which clears all registers and program steps.

Bernhard

[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

[nsg]

Cool project. The box that big would easily house 2 AA batteries for 10 times the energy of 2032. Is there a reason why np25 might not work off couple AAs?

[Brad Barton]

(04-27-2017 04:16 PM)pbnelson Wrote:  I got a great case on eBay for a few bucks and just had to share...

Man, that's a really cool case project. Thanks so much for sharing!
Brad

[Hans-Peter]

A blue and a yellow marker for a better visability of the functions.
A pice of wood on the backside and two bumpers on the chips.
Thats my NP25c.

       

Greetings from Basel
Hans-Peter

[nsg]

(04-28-2017 03:09 PM)Hans-Peter Wrote:  A blue and a yellow marker for a better visability of the functions.

I love the marker idea. Which brand/model did you use?

Bumps are neat idea too.

[Hans-Peter]

It was a Schneider. But I think the most would work.
It should be 3-4 times again, every 5 minutes.

Hans-Peter

[Craig Bladow]

Is there a 3d printed case available for the NP-25? I recently purchased a 3D printed case for a video convert circuit board and am impressed with the quality and the keys, although the legends aren't that readable, that work with the pcb mounted momentary switches, similar to the NP-25.

[jjohnson873]

(07-17-2017 02:46 AM)Craig Bladow Wrote:  Is there a 3d printed case available for the NP-25? I recently purchased a 3D printed case for a video convert circuit board and am impressed with the quality and the keys, although the legends aren't that readable, that work with the pcb mounted momentary switches, similar to the NP-25.

I don't recall if anyone has made a 3D printable case yet. I've yet to see one. My skills with 3D design and FUSION are still a "work in progress". I'm doing some 3D design and have printed out other STL files for a different project. Perhaps later this summer I'll have some time to try to layout a case for the NP-25. Anyone else take a stab at it yet??
~ Jim J. ~

[Craig Bladow]

I took some measurements of the 3d case I purchased, it appears to have 0.1 mm resolution. The keys were rectangular with vertical alignment tabs and the case had corresponding slots to guide the keys.

[jjohnson873]

Since the HP QDSP-6064 displays have escalated in price so much (+$19 ea!); regrettably I'm winding down my kit/assembled NP-25 project. I have 12 kits left with a black pc board color and one partially assembled white one. I can assemble the kits if someone would like an assembled one. I'm keeping the costs unbelievably low because I would like people who want the calculator versus just the three HP displays. The cost of the NP-25 calculator kit is $35.00 USD and the assembled units are $50.00 USD. Shipping costs are a bit extra. Payment is via PayPal.

It was a fun endeavor and I ended up shipping the NP-25 around the world to Sweden, Spain, Germany, Italy, France, Australia, South America, Canada and several other countries I can't recall. I enjoyed providing Chris Chung's NP-25 design and I'd like to thank Chris and Eric Smith for all of their work that made this project possible. For those who have purchased this fun calculator emulator, I hope they've enjoyed playing with their NP-25. If someone discovers a treasure trove of HP QDSP-6064 LED displays in the future and offers them at a reasonable price, I'd start up the NP-25 production again.

If you're interested in purchasing one of the remaining NP-25's, just send me a message to my email at jjohnson873@yahoo.com and I'll send you the details on how to get one. Don't delay, they may sell out quickly!
Cheers! ~ Jim J. ~

[Craig Bladow]

(07-17-2017 02:56 AM)jjohnson873 Wrote:  

(07-17-2017 02:46 AM)Craig Bladow Wrote:  Is there a 3d printed case available for the NP-25? I recently purchased a 3D printed case for a video convert circuit board and am impressed with the quality and the keys, although the legends aren't that readable, that work with the pcb mounted momentary switches, similar to the NP-25.

I don't recall if anyone has made a 3D printable case yet. I've yet to see one. My skills with 3D design and FUSION are still a "work in progress". I'm doing some 3D design and have printed out other STL files for a different project. Perhaps later this summer I'll have some time to try to layout a case for the NP-25. Anyone else take a stab at it yet??
~ Jim J. ~

I have designed a 3d printed case for the NP-25, learning OpenSCAD as I progressed. There are a number of 'refinements' left on the to do list but it is functional. As I thought last year, the key legends are challenging to print legibly using a standard font.

[Craig Bladow]

I've attached screenshots of the design. I've not shown the back cover which attaches with 4, #4 x 1/2 inch, flathead Phillips wood screws. The PCB has one mounting hole which is used with the same size screw as the back cover and a printed washer. No provision is made for a red filter for the led display although one could possibly be attached. The display is recessed a bit which helps somewhat with reducing reflections off of the led modules. The only legends printed are those on the top of the keys, the other functions could be added by an overlay, any volunteers? The power switch (I have the black pcb kit so your power switch could be different) is well protected which also means it may take some dexterity to operate.

Notes on possible future refinements:
1. Rounding the case cutouts to match the keys.
2. Improving the minus, divide, summation and round down key legends as this design currently uses what is provided by "Liberation Sans Bold" font.
3. Widening the Enter key.
               

[Craig Bladow]

First complete prototype.