TI vs Desktop Calculators Teardown - The Electronics Inside

[@qwkimball]

Thanks for the trip in the Wayback Machine! I graduated HS in 1983 and this exact TI-30 was ubiquitous in American schools at the time. It came with a zippered plastic case that was printed to look like denim fabric, with a locker loop on the corner.

[@richfiles]

I have a collection of over a hundred vintage calculators, including desktop calculators that weigh nearly 40 pounds! Some of them are even scientific models, such as my Hewlett Packard HP 9100A. That one was built before ROM chips were even available... It is made using resistor diode logic, and uses transistors for flip flops and NOT gates. To get around the fact that ROM chips had yet to become commercially viable, they created an inductively coupled PC board trace ROM. It was a 16 layer PC board with sense traces running over pattern traces that either zigged or zagged one way or the other across the sense traces. They coded 32kbits of ROM using literally nothing more than zigzagging circuit board squiggles!

[@awo1fman]

I had a TI-30 like that in the early 1980s. I don't remember what happened to it. I might still have it in a box somewhere. Anyway, you didn't show the coolest thing about it, or maybe yours is a later, faster version than mine. You could watch mine "think" with the higher-level operations: the rightmost character would light up a single perimeter element consecutively in a spinning animation for a moment or two before displaying the result similar to a modern video buffering animation.

[@a531016]

This one does do it! It's very clear to the naked eye, but trying to capture it on camera proved very challenging. I think i even tried a high frame rate on my phone, but couldn't make it satisfactory...

[@colindragan9352]

for 0:58 , adding machines are all mechanical, so they use gears, weights, etc to do calculations and are operated with a crank, so I don't think it applies 🙂

[@SeanBZA]

Big difference between them is the cost of the display. The Sharp was using a by them mature technology, but the TI was using a newly developed Monsanto LED technology, that required the displays to be made with each one having it's own silicon chip in the display, so as to grow the LED segments on top of the silicon. Thus a very expensive display to make in large sizes, so the magnifier screen so as to give an apparent large letter while still having a small die. That display easily was the most expensive part of the calculator, so as to cut cost they used the display PCB as the main board, as they could get the tested displays, attach and wire bond them, then check they operated, before putting the top lens on. I will guess the chip pin left out was due to having various models of the calculators around, each with a different mask ROM main chip in it. So they had a place where they could put in an extra select line for the ROM for a function, but this mask version did not use the pin, so it was bent out, painted to prevent shorts, and then, like almost all calculators then, hand assembled in a large factory where labour was cheap. Later versions came with add on ROM modules, I have one, where you plug in additional ROM modules to provide extra functionality, using a serial bus that allows the extra command instructions to be stored. Those use a flexible PCB for everything, one board which holds the display, the plug in sockets formed out of the flex, and the interconnects to the keyboard, along with the main IC chips. Should dig it out, though, as the battery was long dead, I had to bodge in a simple linear power supply to replace it, so it is now mains powered, and simply has a 4V8 1W zener diode, acting as shunt regulator for the power supply. Fed from an old 6VDC wall wart, with a series resistor.

[@a531016]

Thank you for that - interesting to hear the manufacturing process for the display! The expandable ROM sounds fascinating! Would you be interested in seeing more calculator tear downs?

[@oggyosbourne]

I do still have my TI-57 i was given from my granddad that was electronic engineer, chemist and amateurradio operator. Still working fine but the battery package needs to get replaced with new one and better batteries for it. Still using it from time to time.

[@migsvensurfing6310]

Old video and you may have found out that if you open the battery case it contains a AA nicad cell and a converter board. You can use the newer Nimh cells fine. It will run like new.

[@Voidsworn]

I think I have that bubble display ti calculator

[@Voidsworn]

I just checked...nope. I have a National Semiconductor 835A calculator w/the red bubble display.

[@justovision]

I'm don't think the trade off of knowing how to build things that work with mains voltage vs trusting a million really cheap AC to DC converters is a good thing.