Hewlett Packard HP15C

[sP1d3r]

I was recently able to repair a non-working HP15C calculator, it has an ARM RISC processor and is quite a popular model in Hewlett Packard's line of RPN (Reverse Polish Notation) calculators.

It's so popular that Hewlett Packard have released an Open Source emulator and there's also a (relatively) low cost Android app (iOS also apparently) that'll turn any Android 4.1 or newer device into a HP15C.

It has 448 bytes of program memory and retains data after power off with batteries.

There was a small amount of corrosion, (apparently from an LR44 battery but distanced from the battery compartment) which had eaten through one of the pcb tracks, on the lower RHS of the screen position.

HP15C PCB with damaged track

Component side

Track repair

Powers on now

[IanJeffray]

it has an ARM RISC processor

The special "Limited Edition" version did, but those are all HP branded ICs, suggesting it's a standard Nut, no?
This one's also got no "Limited Edition" branding.

[flaxcottage]

The HP-15C is a brilliant calculator. I love it.

It is still popular and expensive to acquire, especially with the manual.

There is an excellent online emulator here

[sP1d3r]

The special "Limited Edition" version did, but those are all HP branded ICs, suggesting it's a standard Nut, no?

Although it's got a 'Saturn' cpu, the numbers on the chips are AFAIK Nut cpu codes, so I don't know about that.

I read yesterday that the cpu is an Atmel Risc processor, but this may apply only to the Limited editions which are circa 2011 onwards whereas the original and subsequent versions, (mine is subsequent to the original) are circa 1985-89.

[IanJeffray]

I read yesterday that the cpu is an Atmel Risc processor, but this may apply only to the Limited editions which are circa 2011 onwards whereas the original and subsequent versions, (mine is subsequent to the original) are circa 1985-89.

Yeah, there's some photos of the insides of the Atmel version here - completely different. It runs a Nut emulator!

[sP1d3r]

It runs a Nut emulator!

Apparently 1LF5 is a Nut cpu code but Saturn cpus have a 4-bit word whereas Nut cpus have a 1-bit word, so it might be doing floating point or something.

[sP1d3r]

Yeah, there's some photos of the insides of the Atmel version here - completely different.

The test circuit is built-in to the earlier versions, it takes about 20 seconds and displays all the screen elements if successful.

Diagnostic running

Diagnostic successful

[sP1d3r]

This is the manual download url from HP, it's dated 2011 so would be for the limited edition re-release version.

The self-test sequence described on p261 doesn't work on the version that I have but otherwise the operation of the calculator would be the same.

http://h10032.www1.hp.com/ctg/Manual/c03030589.pdf

[sP1d3r]

I found this website recently, it's a company dedicated to producing more modern and enhanced versions of Hewlett Packard calculators:

https://www.swissmicros.com/products

Also some useful related info and details if you're into HP calculators.

[Garth]

It runs a Nut emulator!

Apparently 1LF5 is a Nut cpu code but Saturn cpus have a 4-bit word whereas Nut cpus have a 1-bit word, so it might be doing floating point or something.

The Saturn has a 4-bit data bus and 64-bit registers. The Nut has a bit-serial data bus and 56-bit registers. The original 15c pre-dated the Saturn processor. It used the Nut processor.

[scruss]

The 15C is lovely.

Somewhat sadly, I came back from Scotland with my dad's 11C. He was an HP reseller, and this was his pride and joy. Rapid onset vascular dementia, however, has meant it went from something always at the centre of his desk to something he didn't know what it was for.

[BigEd]

Sorry to hear that.

[sP1d3r]

Rapid onset vascular dementia, however, has meant it went from something always at the centre of his desk to something he didn't know what it was for.

Unless you know how the calculator works, you'd be unable to use it for even simple addition or subtraction.
It uses a 4-level number stack, numbers are 'pushed' onto the stack and 'popped' off it.

Programming it is similar to assembly language, I haven't done any yet as I was repairing the calculator for my father.

[Garth]

I found this website recently, it's a company dedicated to producing more modern and enhanced versions of Hewlett Packard calculators:

https://www.swissmicros.com/products

SwissMicros seems to be doing a marvelous job. If my HP-41cx ever needs replacement, I'll definitely get a SwissMicros DM41X. My only complaint is that it lacks HP-IL (Hewlett-Packard Interface Loop) which in many ways is far better than USB, just not as fast. The entire reason I got into HP-41cx was HP-IL, to control, and take data from, lots of instruments on the workbench at once, like an ultra-portable controller. Today I don't use HP-IL very often anymore, but I still want the option. I have all the interface converters too, to RS-232, IEEE-488, and parallel (which again, you can use simultaneously). I do have lots of programs I use regularly apart from the external control stuff though, as the latter has been mostly replaced by my home-made 6502 workbench computer.

Unless you know how the calculator works, you'd be unable to use it for even simple addition or subtraction.
It uses a 4-level number stack, numbers are 'pushed' onto the stack and 'popped' off it.

There are countless stories out there of people asking "Can I borrow your calculator?" only to follow it up with "Where's the 'equals' key?" I found RPN to be very intuitive though, very natural, and later it flowed right into Forth, again totally natural for me. I seem to have an RPN brain. However, I think it would be more natural to more of us if we had been taught math differently starting in the early grades in school, or if our language were that way. I understand RPN comes more easily for example to Koreans, because of their language. For example, where we would say "put on shoes," they would say something more akin to "shoes, install," where you give the data first, and then tell what to do with it.

Programming it is similar to assembly language, I haven't done any yet as I was repairing the calculator for my father.

In the sidebar to my 6502-oriented article "Assembly Language: Still Relevant Today," I tell how early keystroke-programming programmable calculators made it more natural to transition into 6502 assembly language.

[sP1d3r]

SwissMicros seems to be doing a marvelous job. If my HP-41cx ever needs replacement, I'll definitely get a SwissMicros DM41X

Although the SwissMicros calculators are new, the price is competitive with a good condition used original, possibly a bit cheaper.

I think 'push' and 'pop' isn't really relevant to the calculator's operations, the type of stack is LIFO, last-in-first-out.

[Garth]

I think 'push' and 'pop' isn't really relevant to the calculators operations, the type of stack is LIFO, last-in-first-out.

Right. The movement in the stack is mostly automatic. If there's something at the top (which HP calls the bottom, the most immediately accessible stack cell, because they turn it upside down) that I don't want, I do a rolldown. You don't have a number or string in a working register and push it onto the stack though. The top stack item, called X in the X-Y-Z-T set, basically is the working register. The stack is only four cells tall though, which I suppose comes from the days before calculators were programmable and the user couldn't be expected to keep more than that in mind at once anyway, plus the fact that the silicon real estate was very expensive. Four is usually enough; and when you want more, well, then you have to resort to variables.

SwissMicros offers their DM15 and DM15L replacements for the HP-15c. I'm not familiar with the 15c, but it is my understanding that its attraction was its built-in ability to handle complex numbers and matrices. Various modules came about later to give the 41 these abilities. I have the early Advantage module; but there are engineers and programmers making new modules for the 41 even today, both hardware and software, one of the software ones being Angel Martin's 41z which has over 100 complex-number operations, all written in assembly language for best performance and doing the Advantage modules' complex-number functions about ten times as fast, and a couple of his others being his SandMatrix and SandMath.

[sP1d3r]

SwissMicros offers their DM15 and DM15L replacements for the HP-15c. I'm not familiar with the 15c, but it is my understanding that its attraction was its built-in ability to handle complex numbers and matrices.

The HP15C stack can handle 4 complex numbers, an increase of 2 on the HP11C scientific calculator.

SwissMicros DM15L has, as well as the standard rom, two enhanced roms available that can be installed via USB.
One has approximately twice the standard user memory and the other has approximately 4 times as much.
Some of the advanced functions are also enhanced, including matrices, although with limitations.

Whilst the original HP15C is a lot slower than the more modern implementations, it used very little power for such a capable cpu.

There's also a much cheaper version of the HP41C which runs on an Atmel 328 microprocessor, the assembled version has a 3D printed case but it doesn't look much like HP Voyager calculators, url:

https://www.ebay.co.uk/itm/325269384765 ... SwstliteTv

[scruss]

Unless you know how the calculator works, you'd be unable to use it for even simple addition or subtraction.
It uses a 4-level number stack, numbers are 'pushed' onto the stack and 'popped' off it.

And that's one of the great things about an RPN calculator: no-one will every "borrow" it: they try it once, it doesn't work, so they put it back thinking they might've broken it*. It's probably the only reason I have it now: dad worked with an infamous "borrower", who had the audacity to suggest to my dad that his calculator was broken because it didn't work when he tried it. My father, never one to suffer fools at all, replied with a crisp "Good!". It was one of the sales points my dad used when he was a dealer.

The 11C is incredibly frugal on batteries. It's still working on the last set dad installed just before he retired. I remember he commented that these batteries would outlive him, which is now grimly accurate.

But really, my dad doesn't remember how anything works now. The other night I caught him swearing at the cordless phone that wouldn't change channels on the TV.

---
*: shades of the old "Problem Solving Flowsheet" I've seen as office samizdat in three countries and two languages. You know the one: "Does the damn thing work?", etc ... ex US military, as far as I can tell

[sP1d3r]

My Dad bought the calculator back in the '80s, it lasted about 10 years and then it had to be replaced on the warranty.
Subsequently the new calculator lasted about the same before it broke and my Dad then bought an HP48G to replace it.

I found the calculator in his office a couple of months ago and repaired it, he then wanted it back so I'll have to get one of my own!

The 48G can be linked to a PC and has 32K of memory, also it can display the graph of a function.
I expect I'll be having a look at it in the next few weeks.

[scruss]

The 48G is a great calculator. Some years back I found a lot of them in a midwestern university surplus store: all seemingly unused, in their cases, for US $10 each. While it's a much chunkier device that the pocket HP calculators, it has some very useful functions. I wouldn't be without the units conversion functions: it's one of the few devices that does this.

The HP49G was a real disappointment compared to other HP machines: big squishy keys, and lots of time spent "thinking" (garbage-collecting) just when you didn't want it to.

[sP1d3r]

The 48G is a great calculator.

I'm thinking of doing some studies towards a qualification so a calculator with advanced functions would come in useful.
The second hand market for vintage calculators is strong, you won't get much change out of £200-220 for an HP15C, later models such as the 48/49 series still cost north of £100.

[sP1d3r]

In addition to my previous post, the HP48 series of calculators use a programming language called RPL, a combination of RPN and Lisp.

The language can be compiled on a PC and uploaded to the calculator using the serial port or a third party utility can be used on the calculator directly, sounds interesting.

[sP1d3r]

I recently repaired another HP15C with more battery damage, this one had blue powder coming out underneath the display driver chip.

I lifted the chip to check the damage, rather than using hot air I decided to lift each leg of the chip individually using a suitable piece of copper wire with a small 'hook' bent into it because battery damage makes solder reluctant to melt and I didn't want to damage the chip with excess heat.

As it turned out, the track damage was limited to the other side of the PCB which I was able to repair, there weren't any corroded tracks under the display driver chip.

Display driver chip lifted to check pcb damage

After I resoldered the chip it worked ok.

Repaired pcb

[flaxcottage]

Nice one! HP15Cs don't deserve to be consigned to the scrapheap.

[sP1d3r]

Nice one! HP15Cs don't deserve to be consigned to the scrapheap.

I was looking at other calculators from HP and their recent Prime calculators can switch between conventional algebraic input or RPN and can be programmed in Reverse Polish Language and also HP's own Basic programming language, FYI.

[sP1d3r]

I've been looking at the HP48G calculator and it's going up a level from the HP15C, in fact it's more like a small computer than a calculator.
It has 32K of memory which can be used as a repository for programs, data (such as equation libraries) or as storage space for HP48 objects in the stack.

Here's a quick look at the calculator, which has a command line which is like a terminal that can import HP objects from the internal memory, characters from the character set or programs and data from an infra-red and a serial port.

HP48G calculator

This shows the 'Home' screen which is the first 4 levels of the stack, which can be as big as memory will allow.
The white buttons below the screen are for the menu options, in this case the Math menu.

Character set

Equation libraries

Some more of the libraries

Electricity equation library

Coulomb's Law HP48 object

The HP48G has several emulators and also more info on the HPcalc.org website.

[flaxcottage]

A nice looking machine, much better appearance than the TI-series of graphing calculators.

When the calculators got to this stage they lost my interest. They are too slow to use. OK, with a bit of practice one can find everything and for very complicated formulae they may have an edge. However, most calculations are short and swift and I find these calculators too cumbersome.

To be honest I prefer the HP-41C varieties. They cannot graph but I do not need that functionality - I have a spreadsheet.

[sP1d3r]

A nice looking machine, much better appearance than the TI-series of graphing calculators.

When the calculators got to this stage they lost my interest. They are too slow to use. OK, with a bit of practice one can find everything and for very complicated formulae they may have an edge. However, most calculations are short and swift and I find these calculators too cumbersome.

To be honest I prefer the HP-41C varieties. They cannot graph but I do not need that functionality - I have a spreadsheet.

I like the look of it also, but I think that the TI programmables I've seen look OK but this'd be TI 58/59 series which aren't in the same league as HP48 series.

It's the case with HP48 calculators that there's not much point buying one unless you can RTFM, but then this also applies to HP15C calculators, so what's the diff as far as I'm concerned!

Graphing is just a part of this calculator, it's got far more going for it, I think.

I've hardly made a start on the Quick start guide, the owner's manual has over 600 pages, BTW.

[sP1d3r]

I wonder if anyone has an original copy of the HP15C owner's manual?

There's an illustration at the back of the manual, the inside cover I believe, that doesn't appear in any of the downloadable manuals that I've found online.
It's a diagram showing registers r0 to r9, r.0 to r.9 and the index register.
If anyone has a copy of the manual and the inclination to post a photo of the diagram, I'd appreciate it.

Also, I recently found a seller on eBay that sells specialised 3D printed parts and connectors for repairing HP41 calculators which, although as standard they lack the math capabilities of HP15C, can be upgraded with a Math ROM cartridge.

I thought I'd post it here rather than start another thread, I haven't got an HP41 C/CV/CX, repairing one of these is a different kettle of fish than a HP15C.

The seller is divasson, who also has a website, link from eBay item listings.

[BigEd]

There's such a diagram in the 2011 Owner's Handbook for the 15C Limited Edition - see Appendix C, Memory Allocation, starting page 213. (Also here.)

Edit: I see the scan of the Portuguese 1982 owner's handbook has the diagram on page 301 which could well be the inside back cover.

Edit: see also the final page of this PDF, Revision G from 1985. (Via)

Edit: and in better quality and in colour, page 299 here.