Sunday, July 23, 2017

Another 50 Years Ago Milestone

The handheld electronic calculator was coming to life 50 years ago this month.  The patent was filed for in September of 1967 by Texas Instruments, but not granted for another seven years!

It's a foreign concept for us today, with integrated circuits (IC) in everything around us, but in the mid-'60s, they were still new and looking for their place in life.  A while back, I told the story of another TI marketing idea: convincing Regency to produce the world's first transistor radio, the TR-1.  Jack Kilby, one of the co-inventors of the IC, was now a technical leader at TI and came up with the very first "killer app" for ICs. Specifically: a slide rule killer!
In late September of 1965, Kilby called a group of senior engineers, which included Jerry Merryman, into his office for a meeting to discuss a new project. The purpose of the project was to build a small personal-computing device to possibly replace the slide rule. Kilby told the group the device would need to have buttons, it should be battery-powered, and there should be a display mechanism for the answers. He pointed to a book on his desk and said it needed to be about that size (small enough to fit in your pocket). However, it was up to them to come up with a plan for how to do it.

According to Kilby, the idea had originally come from Patrick “Pat” Haggerty, TI’s President and Chief Executive Officer. On a business flight to New York, Haggerty told Kilby that he’d like the IC Dept. to take on the task. According to Jerry, Haggerty was a far-seeing individual trying to come up with new electronic devices that could be created using integrated circuits. Many of the ideas he pitched to Kilby would fall by the wayside; however, that wasn’t the case for the calculator.
Central to the plan was engineer Jerry Merryman, see his biography “Jerry Merryman: the man who killed the slide rule,” (pdf), at the Slide Rule Museum.  Jerry was a perfect example of the kind of guys who were rising to the top in those days.
His technical career began at age 11. At a time when most of us were learning to sit up straight at the dinner table, Jerry was hired to repair radios. Born and raised in Hearne, Texas, he had been an inveterate tinkerer from birth, he says, and played with a Gilbert chemistry set, dismantled perfectly good alarm clocks, and used No. 6 dry cells from the trashcan of the railroad’s telegraph office to power his youthful experiments.
At the age of 18, Jerry got his "First Class Phone" ticket from the FCC (First Class Radiotelephone Operator's License - the FCC stopped issuing them years ago) and became the station engineer for a local broadcast station.  Although Jerry had attended Texas A&M University from 1949 to 1952 and 1957 to 1959, he didn’t graduate. Instead what he had was a diverse commercial and academic background, which included several years of designing vacuum-tube and transistor digital circuits. In 1963, Jerry ended up at TI and quickly gravitated to designing integrated circuits of extraordinary performance for the day.  Jack Kilby chose Jerry Merryman to lead the project, code-named Cal-Tech.  Kilby later stated he thought Jerry was probably the only engineer at the time that could have pulled it off, while also handling the management of the project.
[After the meeting with Kilby]  For the next three days and nights, Jerry worked hard on the logic design. He started out on the first day late in the afternoon by drawing a flip-flop circuit on a board to denote an “Add” button. Then on several sheets of quadrille desk-pad paper, he drew out how to do the arithmetic, how to control the logic, and a rough design of the architecture. What he ended up with was not the complete logic, but it was an excellent starting point. According to Jerry, “It still required a lot more fiddling with.”
As work progressed, the team kept innovating new devices, more complex than ever before.  Truth be told, that was really the motivation behind the project: figure out how to integrate more and more transistors, and achieve higher levels of  integration.  TI wanted to branch out beyond military applications and put ICs in everyday consumer products to showcase their widespread capability. The calculator was a means of accomplishing that goal.
To build a calculator, they estimated they would need thousands of transistors with at least 83% yield. The probability that it would work was practically zero, so Jerry went to Kilby’s office to express his concerns. He said, "The yield of this thing is going to be 0. I'd like to build it in about 16 chips. Each chip will be more complicated than anything we've ever built. It will be a real challenge."

Kilby didn’t agree. He wanted the team to build everything on one big integrated circuit. He responded with a sentiment he was known for: “You'll just have to think of something.”
Their breadboard of the calculator fit on three conventional-size desks positioned together, each with a top surface measuring roughly 10 square feet (2x5).  The goal was to fit this into a shirt pocket.
In 1966, the available transistors used too much power for the calculator. For an integrated circuit with thousands of transistors, Jerry imagined they would need something as powerful as a car battery, yet small enough to fit in your pocket. To solve this problem they needed to figure out a way to lower the overall required power. Jerry knew one way to do that was to go way down in voltage. He reasoned they could do everything with a small battery less than 5 V.
Even batteries that would be a logical choice weren't easily available in 1965.  Nickel-cadmium rechargeable batteries existed but the cells had too high internal resistance, too short a life, and didn't recharge very well.  After consultations with Yardney Battery, Jerry switched the project to silver-zinc batteries; 3 1.5V batteries in series to give 4.5V.  Yardney still produces silver-zinc batteries.

TI is known for their calculator products today, and you'd think this would be their first.  It was eventually released, but the project started in 1965 and it didn't become a product until 1972.  The Datamath 2500 was TI's first calculator product, but the story has a twist.  Before that, TI was a supplier of the ICs for Japan's Canon, whose Pocketronic calculator of 1970/71 was an advanced version of the Caltech project design and one of the first hand-held calculators.  Jerry's original "Project Caltech" calculator came on the market as Canon's product! 
The first Cal Tech prototype calculator, from the Datamath Museum

There's likely to be a few "my first calculator" stories here, so let me start it out with mine.  My first calculator was a simple four function calculator that always displayed two fixed decimal places.  I just remembered the brand of: Rapidman,  After a few Bing searches the closest looking thing I can find is a Rapidman 800.  This was somewhere in my first iteration of college ('73?), and I combined it with a slide rule - in those days most science classrooms had a 6 or 8 foot long slide rule hanging from hooks above the blackboards.  My first scientific calculator was a TI-SR-50.  It's still around here somewhere. 


  1. The first one I ever bought was a TI, but I don't remember the model number.

    The first one I ever saw was an HP-35 that one of the Engineers at Fermilab had.

    Blew me away!

  2. TI-SR10. 1972. It did exponents! Great for studying nuclear physics.

    Couldn't use them in class because of the disadvantage to those still using slide rules (which I used in parallel because I didn't quite trust the calculator yet). Still works.


  3. We were still using slide rules (I had my dad's Keuffel & Esser) when I was in high school, and the first pocket-sized calculator I ever saw was in 1967. It was a Hewlett-Packard owned by a classmate. I don't recall the model number, but he said it cost $350 (his parents had bought it for him).

    I'm fond of the Casio and the Sharp solar calculators. I've stored a few along with other prep items.

  4. A more common place technological shift in this same era was that cassette audio tapes became commonplace, displacing infamous 8-tracks and largely replacing home reel-to-reel units. Anyone remember using cassette tapes for early home computer data storage? I'm not sure a lot of people noticed how fast technology was advancing back then.

    1. I sure do. My first experiences were with an S-100 bus computer a friend had made and moved on from. It was cassette drive. He loaned it to me for a few weeks. After that, I remember using cassettes with a couple of computers, including a Commodore 64 - before we got their floppy disk drive.

    2. Started college with my K&E, a beautiful slide rule that I got pretty handy with. But when the HP35 came out, I had to have one. I remember in a 10 min quiz, spending most of the 10 min. thinking the problem through and when the prof said to hand in papers, I crunched my numbers, wrote down the answer and handed in my paper. So much nicer than "slippin'n sliding" my K&E.

  5. Really enjoyed this article SiG! Great stuff that is really informative.

    I remember sitting outside a car stereo shop when I was buying a new cassette player to replace my 8-track and while sitting in the sun thinking about the smaller format, why it would be better, and the direction of technology. I imagined one day there would be no moving parts at all as the "music" would simply move from some media to the speakers without all the electro-mechanical stuff in between. And lo and behold, some forty years later ... diskless devices. And the beat goes on.

  6. I think I still have a fairly expensive slide rule that I bought in college. Are they collectors items yet?

    I miss my 8 track. One of the advantages of an 8 track is that no album has only favorites. BUT every 8 track album had 4 songs play (or available to play) at once so you just push a button and get a decent song.

    You should look into the demise (or almost complete demise) of Radio Shack. I miss the Radio Shack that used to be here in town. They started going out of business I think when they converted to cell phone stores. They still had a few electronics parts but it was 90% cell phones before they closed their doors.

    1. Are they collectors items yet? Sure - anything is collectible if you find the right collector. I imagine that depends on exactly which slide rule you have. I would guess a 6" plastic slide rule won't be worth as much as a 12" rule made from a more exotic material, based just on how many were produced.

      I have one from Collins Radio; it has the Collins meatball logo on it. (It helps they're in town!). It has specialty scales for microwave radio links. I think it's worth more than the $3 I paid for it in 1982.

      I will hold onto it.

    2. Super cool. I decided I would like one so I looked online. They are between $500 and $750 on eBay. :(

    3. I've still got my big K&E, and a smaller one with fewer scales. Both in their leather cases, and in excellent condition considering how much use they got.

    4. Terry - what are you talking about? I looked up the Datamath calculators and they were under $30. Virtually every slide rule was under $50.

  7. At the same time, I was a Nuclear Reactor Operator in the Navy. We had to perform many calculations for bringing the reactor up to criticality. On one patrol I used my brand new 4 function calculator instead of my slide rule and the Engineer and Captain wouldn't accept my results. I had to start over and do the whole thing using the slide rule. By the way I still have a couple of slide rules around here somewhere.

  8. One of my favorite commercials had the tag jingle "it has big green numbers and little rubber feet". Still miss slide rules............

  9. Now THAT was a walk down memory lane!

  10. It was 1972 in my engineering slide rule class that the professor stated three facts that he strongly believed in. They were that slide rules need no batteries, that in most all cases we will never need the precision of an electronic calculator, and that the HP 35 was a waste of good money. I never finished the class. He was right for a while.

    Remember we built the H bomb with slide rules and all the other hi tech systems of WW2 weapons and follow on aerospace goodies like the Atlas MISSLE.

    Those who loved 8 tracks must remember the Lear 4 tracks. Bill Lear of Lear Jet fame brought us the unreliable tape cartridge and transport mechanism. In 1972 I went to work for Ampex corp in their Miami service center for audiovisual products. I can't tell you how many of those 8 track machines would come in each day from all over and under warranty for repair. Most had tape cartridges with them after having eaten the tape by winding it up on the capstan and pinch roller inside the cartridge. I could go on but I'll keep it short. It was Ampex's venture into cheap consumer products that I believe led to their bankruptcy in the early 70's.

    Back to calculators. Not able to afford an HP I ended up with a TI scientific calculator whose model escapes my memory at the moment. Then there's the Intel story. Remember the 4004 ? Anyone out there with Intel stories ?

  11. My first scientific calculator was also a Ti SR-50(a). I bought it sometime in 1975 or 76. The irony of that is that the Ti calculator is long gone, but the box it came in is still sitting up there on top of my credenza, not ten feet away from me as I type this. Yep, I use a 45 year old box to keep my expense report receipts in.

    1. SR-50!

      That's the one I had. I just couldn't remember the model number.

      The local Junior College bookstore had them on sale for, I think, $100, and I just couldn't pass it up.