Tear Down: Scientific calculator boils design down to two ICs

2/1/2008 9:20 AM EST

Hmmm...its a bit embarrassing for the 35s to run on an 8502 when its big brother, the 50g is running on an ARM9. At least I would go with an ARM7 which is dirt cheap and brings the calculator technology to the 21st century. But I guess thats what happens when you outsource your core design. Disappointing...but I like my 50g.

2/7/2008 6:04 PM EST

Reader feedback:

Dear Mr. Nass,

I read with interest your article about the HP 35s. I have two very minor corrections:

1) The microcontroller is made by General plus, which was spun off by Sun plus some time back.

2) The second chip is a 32Kx8 static RAM, not flash memory.

You wrote that you "(weren't) willing to destroy your 15c (sic) for the sake of this article". The earliest units packaged the LCD display and three integrated circuits onto a module wrapped in black tape (probably antistatic) separate from the keyboard. Peeling the tape reveals the three custom CMOS chips in PQFP packages:

1LF5-0301 "Nut" processor (bit serial, 56-bit word)
1LE2-0321 RAM/ROM/Display Driver ("R2D2"), 6K*10 ROM, 40*56 RAM
1LH1-0302 RAM/ROM (R2D2 with display driver not bonded out)

Later units had a more conventional design with a single circuit board.

Over the years the electronics was cost-reduced several times. The 1LF5-0301 was replaced by a 1LM2-0001, and the 1LE2-0321 was replaced by a 1LH1-0306. Eventually the CPU and first R2D2 were combined into the 1LQ9-0325.

The "Nut" processor was originally designed for the HP-41C, and the variant in the 15C (and related models) is specified for a lower operating voltage but otherwise functionally identical. The architecture is an evolution of the previous two generations of processors introduced in the HP-35 and HP-25.

I've written Nonpareil, a microcode-level simulation for many of the old HP calculators (including the 15C), which may be found at href=”http://nonpareil.brouhaha.com/”target=new”> http://nonpareil.brouhaha.com/

Sincerely,
Eric Smith

2/13/2008 8:22 AM EST

What would I want with an HP-35s? I have an original HP-35 on my desk that is working just fine. I was motivated by all of the anniversary hoopla to put a new set of Ni-Cd batteries in it and it works as well now as it did when new. I'm not so sure about my eyes-- the display looks awfully small!

2/13/2008 10:43 AM EST

I also have an original HP35 made after the error was fixed. I recall shelling out about $400 for it and used it enough to wear the printing off some of the buttons. No longer in use but with a fresh battery it would still operate.

2/21/2008 6:15 PM EST

Ah, yes, the good old days of Reverse Polish, or as some of us put it, Polish Reverse just to be obstinate. Of course, the so-called algebraic calculators were half and half. Just look at something like sine where you entered the number and then pressed the SIN key. That, my friends, is Reverse Polish!
The four-level stack was wonderful. I wish I could have afforded one of the original 35's when I went to school, but alas, a slide rule was all the budget would allow. Might have made better grades with one. Sigh.

2/21/2008 6:20 PM EST

Gee, i guess I'm dating myself when I tell you that my room mates dad bought him an HP35 in 1973 for $800 (probably the equivalent of $7-$8 K now or more). we had three of them in our phyusics lab and they were locked down to the bench. It was called a slide rule calculator at the time, not a scientific calculator. folks were not allowed to take a calculator in to exams because most people could not afford them. times do change

2/21/2008 6:39 PM EST

I still have and use my HP11C - haven't replaced the batteries in 8 years!

2/21/2008 6:57 PM EST

Sorry to be picky, but the Commodore 64 used a 6510, which was basically a 6502 with some extra I/O pins and a tristateable address bus. The 6502 was used in such pioneering computers like the KIM-1 and AIM-65 and was popularized by the famous Apple II and Commodore VIC-20.

2/21/2008 7:39 PM EST

In 1973 the HP-35 changed my life. It allowed me to try things I would not have, simply because the math computations were too laborious. I discovered active filters among other things and made a virtual career of them. What a machine.

2/21/2008 8:10 PM EST

$800? Retail on the HP-35 was $495, which went down to $395 when the HP-45 came out later that same year. My HP-45 (bought for $425 in late 1973) still works but has some burned out LED segments and was replaced by a HP-48SX, which does still work great. Like Contraption points out, the 6502 was most famous as the CPU in the Apple ][ (also have one of those sitting in the lab).

2/21/2008 11:49 PM EST

Still waiting for a remake of the 15C at least its form factor. I broke down and bought the HP-12C not for its financial buttons but for RPN and its size. I have the HP-33S and I get depressed every time I see it. I have to remember the the days when I worked all summer and winter in school and bought a HP-41CX, IL-loop, Dig Tape Drive and IL printer. I regret trading the CX for a HP-48G for $60. I bang my head on the wall every time I think about that trade. In a way, my career in computer engineering got an enthusiastic boost being creative with calculators. Writing a word processor program for the 41CX was the ultimate. Every key was mapped including ways to insert special characters. The IL printer printed out papers I wrote for school projects. The digital tap drive served as virtual memory and the CX memory as a cache. The program continously ran while I typed up sentences - to intercept keys and insert characters in memory. Those were the days. I still have the IL devices. Not sure what to do with them without the 41.

2/22/2008 3:44 AM EST

My boss gave me an HP35 shortly after they came out - could swear it was about 1963. It took some serious rough treatment - but never failed. When I left the company I had to give it back - bought an HP25 , it was within my means. A few years later I upgraded to an HP41CV, with printer and some plug-ins. I later purchased an HP42S. They all still work fine, although the HP25 is a bit intermittant due to the fragility of the electrodes in the battery box - and it's been dropped a hundred times, just like the rest of them. The 42S is my favorite and is the one which most nearly emulates the HP35 for ruggedness - but is way more powerful.

2/22/2008 8:36 AM EST

HP calculators are great for everyone, not just for engineers. When I started college (chemistry) in 1984 my brother (then a civil engineer, who used a slide rule in Rangoon Institute of Technology in 1970s) told me to get an HP calculator so I bought an HP 11C (Cdn $130). I was a poor new immigrant to Canada that time and didn't know how expensive that was (compared to other brands). I later gave it to my niece (now a dentist) but she lost it in college (the loss broke my heart). Another brother (now a pharmacist) still has his 11C, also bought in 1984, which runs perfectly today. His 11C always won speed competition in high school with other non-RPN calculators. I bought three more HP calculators while in EE school (1989-94): 28C, 28S, 48SX. I later gave 28C to my other brother (geological engineer) because his old HP (LED display) calculator quit working. My sister (a physicist and a botanist) also uses an HP 32S (on my suggestion). Of those, 11C is the tough one. One time, an HP salesman threw it on to concrete floor in front of the U. of Manitoba bookstore to brag it's tough. I wouldn't do that to any other HP calcluators I own though. I will definitely buy another 11C or 16C today if it's available (but not at outrageous antique prices on ebay). Imho, 11C, 15C, 16C are the only 'tough' and useful calculators, which 'fit' in the pocket and I'm sure they'll sell well if they were re-introduced. 28C/S are full keyboard but so flimsy (for an HP) and 48 is just too bulky (and illegal without a masking tape at U of M exams in 1990s) but it uses AAAs. If I can get it my way, I want to see a new RPN calculator in total black with big white alpha-numeric labels, bevelled keys with smoothed edges (angle slanting degree is just fine), easy to read text and radix marks, easy to read secondary key labels (orange is still perfect but no purple, please), and 'tough and small'. In this day and age, cheapness prevails (in price and quality) so I may be just dreaming.

2/26/2008 1:34 PM EST

Dear Mr. Nass,
I read with interest your article on the HP35s in the 2008 February issue of Embedded Systems Design. I, like many others, have long lamented the absence of availability of HP's RPN calculators. My favorite HP calculator was the HP29C.
In your article, you mention that the HP35s has an LCD display. I greatly dislike the use of LCDs in calculators, as in the HP48GX, which I presently own. Except in the presence of bright light, it is difficult to read an LCD. If calculators had LED readouts, I would be one happy engineer!
I believe that long battery life is not the dominant requirement in a calculator. At least not for me; and I would surmise that I am not alone in the world with this preference. I would much rather have an LED readout, rechargeable batteries, and a charger ("wall wart"); e.g., as in the HP29C. In my office I would gladly plug my calculator into its charger, and then unplug it and take it with me when I left the office. Furthermore, in the past couple of decades, battery technology has improved substantially, so that a calculator can run on batteries for a longer time between charges than on the old Nicads.
Please, ladies and gentlemen of HP, bring us back some RPN calculators with LEDs and chargers. Ignore the "marketing" folks and do your own surveys of people working on the "front lines".
Best Regards, McSquared

3/6/2008 11:47 AM EST

Hey TADA, you mention that you had an HP-45 but that it now has some burnt-out LED segments. I have a colleague that had an HP-21 with a supposedly burnt-out segment, but it turned out that the super-fine wire connecting the segment on the LED wafer to the pad on the PCB had come undone. I managed to resolder it with a needle-sharp soldering iron. Perhaps the same could be done for your HP-45?

6/26/2008 4:26 PM EDT

The following letter was sent in via e-mail from a reader:


In the HP35s teardown article from February issue of Embedded Systems Design, you write:

"The 8502 is designed by Sunplus
Technology, a Taiwanese company.
It’s based on the 6502, an 8-bit
processor that first appeared on the
Commodore 64 computer, which was
popular around the same time that I
purchased my 15c."

Whoops! The 6502 was already quite mature by time it appeared as the more highly-integrated 6510 in the Commodore 64; it had already appeared in the original Apple 1 computer in 1976, as well as the Commodore PET and Apple II-family. Wikipedia correctly lists at least the Atari, BBC Micro and Commodore VIC-20 as well.

You might have a quick look at Wikipedia's entry for the 6502--it looks pretty accurate, at least to my recollections of 32 years ago (ouch).

--Dana Myers