Programming an HP-15C (2013) | Hacker News Reader

Programming an HP-15C (2013)

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86 pointsluu59 comments

I bought a 15C new. I still have it on my EE bench (replacing my slide rule, of course). Every 8 or 9 years I replace the three LR44 batteries. And writing little programs to tickle the Inner Nerd is always fun. HP: we miss you!

Mine was bought new well over 30 years ago. It is sitting on my desk within arms reach and I use it regularly. I have replaced the batteries two, maybe three times in all those years. The battery life of this thing is magical.

I have been using HP 42S for the past 15 years and would not replace it for any other. It is a pity that the LCD fades out in these and now it is only possible to see it at specific angles.

You may be interested by this [1]

The device is reliable, the screen is amazing, the USB connectivity brings a lot of value and the community on SwissMicros' forum are passionate HP people.

I'm not affiliated with them in any way, just an happy geeky customer :)

[1] https://www.swissmicros.com/dm42.php

Seconded. Their replicas are amazing, even better than the already awesome originals. I own a few, only god knows why :)

Maybe I'll ask to be buried with them, so I can be dug up in a few thousand years and worry archeologists ;)

I think the "someone who brought it back" is Swiss Micros, which makes a compatible calculator (which they call DM-15) as well as other models in the same family. They say their chip that emulates the original cpu is quite a bit faster than the original.

https://www.swissmicros.com

Wow they also have one based on the 42S.

I also want to mention the HP-45 iPad / iPhone app; it runs the exact microcode of the original on a VM. (My buddy was involved in this, and makes some $ - but I bought it and really really like it, and this isn't an ad, etc, etc.)

I have a 42S emulator running on my iPhone, but it really isn't the same as being able to press physical keys on a hardware device.

One of the charms of these devices was that they were built to last. ie: the keys were injection molded with two colors of plastic so they wouldn't wear down. So, while I still have a couple of working HP's from the 80's, I've been through a dozen or more mobile phones in about the same time...

They're called doubleshot key caps. The better mechanical keyboards also use this method. The HP-15C and others in that line were exceptionally well made, with the PCB for the keyboard being ultrasonically welded for rigidity.

I have actual 42S. The physical device lasts very well but the LCD fades out as it gets older. Right now mine does not have enough contrast to read it looking at it directly. You need to look it from downward angle and in perfect light.

Other than that this is the best calculator ever made.

At the time I bought my 48SX, I remember briefly considering a 42S. I had a lot of fun with the 48, but in retrospect, I'd have gotten more use out of the 42.

(But what I really regret is not having bought a 16C.)

HP still makes a decent HP-15-like calculator:

https://en.m.wikipedia.org/wiki/HP_35s

The HP store shows many of their remaining 7 (!) calculator models out of stock quite often. I'm not taking any bets on how long HP is going to make any calculators at all. I feel sad every time I visit their store...

They already stopped making any kind of graphing calculator, apparently.

Hp prime?

No longer on their (hp) store. Still can get unsold inventory on eg amazon

HP ported their calculators to iPhone and Android apps. Most people who want an HP calc probably just use those now instead, except for the few who want the tactile feel of calculator buttons.

For the discerning STEM student/professional, 15c is the only relevant RPN emulator on mobile officially released by HP and it's an overpriced disappointment IMHO.

HP didn't even extend a courtesy reach-around for our CS/CpE brethren with 16c integration despite their $16.99! Even if you were in the market circa 2011 to pre-order one (or a few) 15c LE--which came with a copy of the desktop app--you'd still have to pony up even more for the mobile app!

On Android, I'd highly recommend skipping the "official" HP garbage and supporting CalcTastic Plus[1] for a mere $0.99. Even the free version makes the HP emulator look like a complete joke. I've been rolling with a 35s as workhorse since undergrad days, but couldn't care less if today's zombie HP literally disappeared from the market tomorrow.

[1] https://play.google.com/store/apps/details?id=com.shaytastic...

Good info, thanks for the update!

HP themselves also briefly brought it back about a decade ago as a limited edition model that runs ~60 times faster than the original, running an emulator on an ARM microcontroller.

I've really wanted one for a while, but they're so expensive. Maybe one day.

Faster is not necessarily better here. My HP-12Cs have been going on their original batteries for more than 10 years each now, but I expect a faster processor would mean shorter battery life.

Wow that sounds a lot more complicated than the one I had, HP 42S, because you had to use codes for the instructions instead of just pulling up the instructions in readable ASCII.

I found this random example of entering a program on a 42S: https://www.youtube.com/watch?v=JQMOOxup8bI Coincidentally, it even uses the FP (fractional part) and X=0? test that the OP mentioned.

I wanted to see what programming the 15C looked like, so I found this as well: https://www.youtube.com/watch?v=m4dF5nF8I88 Looks like you can enter the program without knowing the codes, but reviewing the code just shows codes.

> Wow that sounds a lot more complicated than the one I had, HP 42S,

Yeah... the 42S derives from the earlier 41 series, and the 41 series was the first to use alphanumeric symbolic names for programming commands. Prior to that, there was always a very direct correlation between the button you pressed on the keyboard and the way the command was encoded in memory. (Which made sense given how resource limited the earlier calculators were.)

HP took this evolution one a step further with the HP28C, which was released a few years past the 41's. The 28C introduced a garbage collected heap and a tagged type representation for objects that gave you something essentially like a small RPN Lisp running on a handheld.

I used an HP41 for many years but it eventually died and I didn't really use an engineering calculator enough any longer to justify either repairing it or picking one up on eBay. I really liked the ergonomics and, although I have an emulator on my iPhone, it's not the same without the physical keys.

I did pick up a 28 at one point but never really bonded with it.

> I did pick up a 28 at one point but never really bonded with it.

IMO, the 28 and follow ons lost a lot of the focus of the earlier (more 'primitive') devices. They were more cumbersome to use, and whatever marginal improvement they offered in functionality didn't matter because everybody started to use PC's, laptops and the like.

I consider HP-28S a work of art. The programming language can be described as an effective mixture of Forth, Lisp and even APL and J. The memory was also very efficiently used, the HP-28S had whole 32K! (not a little for that time).

And all that with 4-bit CPU (!) which worked for a very long time on very small batteries.

https://en.wikipedia.org/wiki/HP-28_series

> I consider HP-28S a work of art.

I'd extend that to the whole HP calculator lineup through about 1994 or 95.

There are a lot of aspects I could single out, but William Kahan's involvement in their numerical algorithms is a particular standout for me. They wanted high quality numerics out of battery powered 1970's era micro-electronics, so they brought Dr. Kahan in to design the algorithms necessary for the task.

(Dr. Kahan is also noteworthy for his involvement in IEEE-754, which is still the standard for floating point today.)

Serious, serious engineering went into these calculators.

What would you say is the final model that "has it"? Besides my vintage HPs (HP15C, 2xHP16C, HP45) I also have the 50g and the modern 35S. For me, the 50g's lack of a proper ENTER key ruins it. I'm sort of on the lookout for a nice 48 series to replace it for that reason. The 35S at least has a proper ENTER.

> What would you say is the final model that "has it"?

For me, at least, probably the combination of the 48GX and 42S. Both represent the end of the line of HP's traditional hardware engineering, which is such a significant part of using these devices. The software gaps between the 48GX and the later 49 can be made up by installing software into a 48, if that turns out to matter for you.

One of the more significant new parts of the 49 software is the "Meta Kernel", which was externally developed by Jean-Yves Avenard as a 48 extension. IIRC, Avenard ultimately wound up working for HP on their calculators, which I believe is how MetaKernal wound up as part of the core 49G ROM. IIRC, this was also a bit of a reconstitution of HP's calculator engineering effort, as the previous team had been disbanded a few years prior. (ie; William Wickes, who was heavily involved in the 41 and 28/48, wound up at some point working on video conferencing systems for HP.)

The reason I'm also including the 42S is that it's a lot more traditional in the way that it operates. If the 28/48/49/50 series feels like a small handheld computer with a custom programming language, the 42 feels more like an actual calculator (with a lot of capabilities).

Thanks for your reply. I’m certainly going to keep a lookout for both.

I still have my original HP-15C from 1987, along with two SwissMicros DM-15L (I had also purchased the official HP reedition HP-15C LE, but one was stolen from work in a burglary, and I resold the other one at a tidy profit, the DM-15L is much better). I also have the official HP-15C iPhone app. And a HP-48GX, HP-33S, HP-35S, DM-42L.

To be frank, it's the only one of my HP calculators I can remember how to program, it's extremely simple, unlike newer models.

HP reedited the 15C manual for the limited edition:

http://www.hp.com/ctg/Manual/c03030589.pdf

I still have my original hp-15C and the owner's handbook with a print date of 2/84

The HP codes aren't too bad because they correspond to the location of the keys on the keyboard, i.e. y^x is 21 because it's the second row and first column of the keyboard. If you want something really confusing try programming a Soviet Elekronika calculator, they actually work fairly similarly to the HPs but the codes displayed on the screen when inputting a program are in hexadecimal displayed with weird symbols because you can't actually show A-F on a seven segment display.

Ah, I forgot all the fun I had squaring EGGOGs.[1] I'm working on fully documenting the MK-52 in English but I've been sidetracked with school.

[1]: for the uninitiated, when you'd do anything meaningful on the MK-52 (or 61 or one of the other ones in the series) you'd get an "ErrOr". the "ErrOr", in cyrillic, looks like "EGGOG" because "r" and the cyrillic g look similar, so a lot of people call them EGGOGs. sometimes you could square them and do other things to mess even farther with the calc. in my research I've found that there are more undocumented functions than documented, a lot have to do with the EGGOG manipulation and isolating them and entering that into a program. wild stuff

> you can't actually show A-F on a seven segment display.

Yes you can - I used a 7 segment display with hex numbers (a 6800 Dev kit of some kind) - A, b (lower case), C, d (lower case again) E, F are all straightforward.

See https://en.m.wikipedia.org/wiki/Seven-segment_display

I've typically seen A-F rendered like so:

   _         _        _   _
  |_|  |_   |    _|  |_  |_
  | |  |_|  |_  |_|  |_  |

(Variations would be a double-story lower case 'a' and lower case 'c'.)

But if they cloned the 7447 decoder they'd look like

                   _     
     _    _   |_| |_   |_ 
    |_    _|       _   |_

with 15 blank.

Given how hard it can be for me to focus when the web is just one click away, these dedicated tools are such a boon. Plus the hacker touch of these programming languages has something lovely.

(I don't get what's so funny with the 38x3, though...)

Yeah - I'm not mathematically inclined enough to understand what would be so funny about the 38x^3 denominator either?

Unless it's something that would cause an error due to memory/register size constraints, or cause the calculator to sit there forever on some of the other larger squares or test values due to 1986 speed of the ALU or whatever is in the calc?

My gut assumption is that it's some mathematics inside joke of some sort...

All of the other constants are expected. 1, 2, 9, 10 ok those make sense. Where does 38 come from? Ha ha. So random.

I could not have put it better myself.

    1 + 2 = 3
    3 * 9 = 27
    27 + 10 = 37

off-by-1 #laughter

Related: it’s been sad to see the HP48 emulators bitrotting. m48 is no longer available on the App Store, and I can’t find anything that works anymore for the Mac.

There's a port of Emu48 to MacOS

https://sourceforge.net/projects/emu48mac/

Kinda Mac-related is i48 for iOS:

https://apps.apple.com/us/app/i48/id329454950

hpcalc.org has a list of emulators:

https://www.hpcalc.org/hp48/pc/emulators/

Best seems to be Emu48, as mentioned above:

https://hp.giesselink.com/emu48.htm

x48 is open source, like Emu48:

https://sourceforge.net/projects/x48.berlios/

Unfortunately I couldn't get any of em to build anymore. Emu48 is definitely the best, but it needs help to build on new MacOS. x48 doesn't build anymore, and is also X11 based, which is not great on Mac anymore either.

Gosh. I got lucky that the m48 from my 6s restored successfully to my 11 pro. Love that software.

I have both the HP15C and two HP16Cs, though I am not old enough to have bought one new. :o) Truly awesome calculators, even if they are a bit slow sometimes. The form factor of the Voyagers is amazingly perfect; in fact the ratio of the length to width is approximately the Golden Ratio if I recall.

I use mine regularly as I prefer a tactile instrument. Plus the mental challenge of implementing programs in a constrained environment is invigorating.

Upvote because I still own and occasionally use my HP-11C. It may be on its 4th set of batteries, after 30+ years. I haven't written code on it for 20yrs, but the last was a sight-reduction program for celestial navigation. I do have and use emulation of HP-15C on every computer I cam, plus my phone.

Oh, yeah, I wrote a Brainfuck interpreter for those https://steemit.com/programming/@michaelzinn/babbage-s-diffe...

I also did a C64 BASIC compiler in Idris for it, if you have a copy with over 800 lines of program memory you can play HAMURABI on it: https://forum.swissmicros.com/viewtopic.php?f=23&t=2193

I strongly recommend that calculator, it's a great programming toy.

I'm currently implementing a concatenative language, and have added OP's program as an example: https://github.com/pflanze/copycat/blob/master/examples/hp.s...

This is closer to how the later HP models worked, where naming and quotations are available (via « »).

(I happen to have had an HP-15C as well as my first calculator :)

I still have mine and the user manual sits on a shelf in my basement. I bought mine in a private deal from a guy whose father was a distributor. Cost me $110 in 1984. It allowed me to invert a 4x4 matrix, thereby earning me an A in my power engineering class. I programmed a sinc function to the amazement of my linear systems instructor. And I programmed complex multiplication and division routines. This was pretty cutting edge back in the day, long before mathcad.

Reminds me to start collecting HP calculators. I have a few, but would like to collect all of them and put them in a display case. Anything non-RPN is an abomination.

Are you familiar with www.hpmuseum.org? Collectors and users of HP calculators hang out there. Hp41.org is great for the HP41

The other day I ran into a guy throwing stuff at the junkyard, in the bag there was a calculator, so I picked it up. HP 40G ..

I was so happy, until I put batteries in and realize there's no RPN in the rom. The device is unusable (to me)..

poor HP

On a different note, I stumbled on my TI-Programmer LED calculator and power supply a few days ago. I plugged it in, but no response. I guess rechargable batteries weren't meant to last nearly 40 yrs. I am now obligated to attempt resurrection. In case I need octal, hex, or bit operations.

I have an HP 200LX that I acquired recently. I have been using it for writing mainly, it's pretty fun. I also have an old PCMCIA Ethernet card that I want to use with the 200LX so I can connect to IRC (mainly for Twitch chat).

I have one from my grandfather and one from my father. Amazing things. I wonder what device I should leave for my future children! Maybe my Ti-83...

I use a magnificent HP emulator called nonpareil for almost all my RPN needs (the rest being covered by dc and xcalc -rpn).

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