Mar 302024

Though vintage programmable calculators remain one of my oddball hobbies, it’s been a while since I last mentioned them in this blog. And it’s especially rare that I’d write about a non-programmable, perfectly ordinary, dirt cheap, dollar-store quality mass-produced Chinese scientific (“56-function”, standard chip) calculator, but this one is different.

Why? Because I fixed the darn thing, that’s why.

Why am I so proud of my accomplishment, fixing something that most folks would have thrown away as a worthless, broken piece of junk? There is a very specific reason.

The bane of cheap calculators for the past 20-odd years has been the connection between the calculator’s main circuit board and its liquid crystal display. The liquid crystal display contains transparent connections, but these, rather obviously (it’s glass!) cannot be soldered. So how do you connect the display and the circuit that drives the display? In the earliest LCD devices, this was accomplished by a strange, rubbery part, a conductive silicone “zebra strip” that made an electrical connection between a series of connectors on the circuit board and the corresponding leads on the display glass. The device worked if this zebra strip was properly sandwiched between the display and the circuit board and held together tightly, which required an appropriate mechanical construction.

More recently, these have been replaced by, ahem, I think they’re usually referred to as “zebra stripes” or maybe “zebra lines”: essentially, paper-thin sheets of plastic with parallel conducting lines. A short strip, or stripe, attaches on one end to connections on the circuit board, and on the other end, to the LCD display. The attachment is adhesive (which may be heat activated) and once attached, there’s no need for mechanical pressure to hold the parts together. This, I presume, makes the design less constrained, and reduces manufacturing costs.

The problem is that these zebra stripes can become detached. This leads to a failing display: Digits vanish, segments vanish, crosstalk appears, the display becomes garbled and unreadable.

In some cases, this can be reversed by (very) carefully pressing down the stripe on both ends, with a hard but not too sharp tool as you wish to apply pressure to reattach the adhesive, not destroy the plastic. Sometimes, a heated tool works better. But the result is uncertain: Sometimes it works, sometimes it doesn’t, sometimes it fails a few hours, days, weeks later.

If the zebra stripe is mostly or completely detached, or if it is damaged, the device is dead. Or so I thought… until now.

When this nameless “scientific calculator” came into my possession (found in a small bag of goodies that we bought at a thrift store) it indeed seemed hopeless. But I decided that it can serve as a perfect test case. For the first time ever, I endeavored to purchase a small piece of replacement zebra stripes of the right size from AliExpress. I had no idea how to use it properly, or indeed if it would work or not, but I figured it’s worth trying.

My first few attempts were disastrous. Applying too much heat destroyed the zebra stripe. Glue and molten plastic residue contaminated both the circuit board and the LCD display. Scraping it off was difficult and I was probably one bad move away from cracking the display.

But I didn’t. And on the fourth try, the display more or less came to life! I was ready celebrate success even though the display was not quite flawless, as it was already a far better result than I had hopes for. But at this point I noticed that although the display was now working, the calculator itself wasn’t: it no longer responded to any of its keys. I went through several iterations trying to troubleshoot this new problem before I noticed something: The zebra stripe I used was a tad longer than it should have been, and it made contact with another lead on the calculator’s circuit board, effectively short-circuiting its keyboard.

Once I corrected that, the calculator not only came back to life, even its display was now working like a charm. I feel like celebrating.

I don’t know how long it sill last: Cheap hardware is still cheap hardware. But now I know that repairing broken zebra stripes is possible.

So yes, this is how I am having fun during the long Easter weekend. Happy Bunny Day!

 Posted by at 3:03 pm
Mar 272014

It was less than 24 hours ago that I wrote about the death of a friend and now I have to do it again: I just learned that Palmer Hanson died a few days ago, after a prolonged illness.

Palmer’s name was well known to the calculator enthusiast community ever since the days of the friendly rivalry between owners of high-end Texas Instruments and Hewlett-Packard calculators in the late 1970s. Palmer was famous, among other things, for writing one of the fastest calendar printing programs for the TI-59 calculator. Though I never met Palmer in person, over the past decade and a half I corresponded with him many times, on account of my Web site dedicated to programmable calculators,, and the archival material that I publish there.

It was only a few weeks ago that I received an unexpected parcel from Palmer, with a batch of rare newsletters that he sent to me for scanning and Web publication. I gladly complied. Another batch of newsletters followed shortly thereafter; this batch is still sitting on my desk, as I’ve been busy with work lately and have not had the time to do the scanning.

Therefore, I knew that Palmer was gravely ill, but I was nonetheless hoping that he would stay with us for a little while longer. Unfortunately, when our time comes there is not much we can do, and Palmer’s time came after a long and, I sincerely hope, happy life.

Googling his name just now, I came across a video of a presentation he gave less than two years ago, at HHC2012:

Good-bye, Palmer. I feel privileged to have known you, even if it was just online.

 Posted by at 1:13 pm
Dec 212012

I spent some of my time today building a calculator.

I still know how to handle a soldering iron, but this time around, the design is not of my own. The credit goes to Michael Berger, a calculator enthusiast in Germany who decided to resurrect a classic East German desktop calculator, the Robotron K-1003 in the form of a microcontroller-based kit.

And thanks to Michael, I had some pre-Christmas fun. But now that the calculator is up and running, I feel compelled to find its original German-language manuals and understand its programming model.

 Posted by at 10:22 pm
Oct 142012

It’s rare these days that I add a new calculator, even a not particularly exciting non-programmable model, to my “museum“, but the other day, I did find an old Sharp 4-function calculator that was previously unknown to me in a thrift store: The Sharp EL-102M.

Sharp EL-102M

 Posted by at 10:29 am
Oct 022012

It’s not every day that I can actually add some new information, however trivial, to the “interwebs”. But today, I received a question from a calculator enthusiast. He wanted to know the meaning of a mysterious “BM” or “BN” logo that he found on the back of a vintage Sharp pocket computer:

I have seen this symbol many times before. I thought I knew what it meant but suddenly, I was stumped. What was it? A standards organization? A quality logo? Something else? Google was of no help either; I was searching high and low but couldn’t find anything even remotely resembling this strange sign.

Then I looked at my collection of scanned calculator manuals and sure enough, on the cover of a vintage Casio manual, I found it. Same logo. It even had some text next to it, but it was not legible. So I started searching my library of paper manuals.

Much to my disappointment, while the logo was present on a few of them, it was not much more legible than the one on the scanned copy. Eventually, I came across a manual that contained a semi-legible version:

So this is it. The logo reads, in case the above is not sufficiently legible:


Recognized by

Mystery solved. And while I nave no clue as to why information about this once prevalent logo is not readily available online, I can confirm that searching with the above full phrases on Google reveals nothing relevant (with one exception; searching for the strings “BM MARK FOR” and “HIGH QUALITY” yields one relevant hit, a scanned PDF copy of the Canon Palmtronic F-7 manual from the Web site of Katherine Wasserman). Well, I guess that is going to change now.

 Posted by at 3:37 pm
Jun 052011

Years ago, just about every visit to a thrift store yielded a new and interesting addition to my little museum of programmable calculators. Not anymore… the ones still missing are unsurprisingly the ones that are quite hard to find, and in any case, truly vintage calculators are becoming ever more scarce. (I suspect it has to do both with their age and the fact that far too many people discovered eBay.) So it came as a pleasant surprise that the other day (when I made a sad final visit to the veterinary hospital for Tarka’s remains) I found not one, but two vintage calculators in a thrift store along the way. True, they’re not programmables, just ordinary “four-bangers” but they’re certainly vintage alright: a somewhat unusual red LED Lloyd’s brand calculator and a first-generation “yellow LCD” model from Sharp.

 Posted by at 7:48 pm
Nov 062009

I just added some new calculators to my ever growing online museum. Two of them are programmables: an Aurora SC-180 and a Casio FX-770P. I also added several non-programmables to the “photo album“: a Btech fx-82LB scientific model (obviously, a Casio clone), a Canon P3-DII, a Cedar CD-420, a Corvus 322 (this is a real vintage machine), a Lloyd’s Accumatic 310 (similar to my first ever calculator), a Sharp EL-531RH, and an Underwood 340 (this is a really ancient machine, printer only, no display). I also added two calculator-like non-calculators: an “RV Special” databank and a handheld Sudoku game.

 Posted by at 1:57 am
Nov 042009

Here’s another fine example of a somewhat Orwellian interpretation of Draconian copyright laws: according to Texas Instruments, hacking your own pocket calculator is illegal.

Recently a friend of mine, responding on the bureaucratic nightmare surrounding the H1N1 flu shots, remarked that “it’s enough to turn one into a Republican”. What can I say? Acts like those of Texas Instruments are, on the other hand, enough to turn one into a commie. After all, when corporations treat their own customers as the #1 enemy, what is the customer to think?

 Posted by at 5:17 pm