Exactra 20

Recently, I was given the opportunity to hold one of the very few important items in history by a very good friend of mine. Never in my life would I expect to come across it. But then again, there are a lot of things not possible for me except to visually enjoy them throught the Internet. So, while it was briefly on loan to me, I took a few shots and also opened it up because the keypad was not working. But in the end, because of its importance, we agreed that it is best left as the way it is: You can switch it on and play with the other switch to change the display but that is all the calculator can do as it is too risky to open up the sealed keypad.

This is the Exactra 20 from TI or better known as Texas Instruments. This is a four function calculator (you know, add, subtract, multiply and divide) manufactured in the early 70's (around 1974). And also, one of its parts were used in Obi-wan's Lightsaber in Episode IV's Star Wars.

During that time, when a prop was being created, prop artists would use a lot of ready-made items or go looking for items from either a perfect/broken item to strip from. Some would be obvious (like the coffee making machine turned into the De Lorean's fusion nuclear reactor in Back to the Future) and the rest could take years to identify. And once found, it would become expensive overnight.

Many fans would scour all over the place just to get the right item to make their own porps. No one is really content with a replica. The feeling of making your own favorite prop with the exact items is priceless. Like my friend, it is not the item that makes it worthwile but the journey to complete it (or something like that. I was busy eating my fries, OK?)

This 70's calculator was shown to me to see if I

could repair its suspected broken keypad. But
because of its significance, I dare not break it

Want to know an engineering marvel? The whole
calculator is held by just two screws. Everything
else is snapped into place.

The red filter is snapped on to the casing. In terms
of manufacturing, this could mean less cost as there
is no need for other items such as glue or screws

The instructions are molded onto the back of the
calculator.

The calculator takes in three "AA" sized batteries
Compared to the modern energy efficient LCD
style calculators which uses either solar power
or just a button cell battery

Just like its modern day equivalent, everything
is built onto a single printed circuit board. But if
you look at the components, you can guess why
it needed so much battery power.

Personally, I think the keypad is wonderfully designed
for its time. But in terms of repairing, this is going to be
a very hard component to open up and close it back

A piece of "paper" is used as an electrical insulator
to make sure the main circuit board components
do not electrically short the ones in the keypad
and the LED display

The keypad is attached to the main circuit board
by soldering its metal connectors

This is the part which gets me: The two-inch long seven LED
bubble display. The bubbles magnify the small red LEDs which
was quite cool at that time. Normal Exactra and other bubble
calculators had 6 bubbles but only the Exactra models 19 and 20
have seven where the seventh is used to display the "negative"
sign. But for Star Wars Fans, this is one of the parts used in the
Episode IV's Obi-Wan's Lightsaber

This is how the display looks like when switched on

And if you flip the second switch, the one with the
"$" sign, the display gives you two decimals numbers