Object Deconstruction – Oversized Calculator (Will Knowlton)

When I was at Goodwill looking for something to buy, I immediately went to the back of the store. I was drawn to the archaic and decaying receivers and tape players. Next to these I found a large Casio calculator and liked how the buttons felt “chunky” and fun to press. I decided to purchase this and take it apart. img_0321

I started with the four screws on the back corners of the Calculator. Then I took a flathead screwdriver to it and popped off the backing.

Underneath the hood you find a PCB, and the LCD screen for the calculator. I then started looking carefully at the PCB, to see if I could identify what was going on. I determined the center of the board (big black dot) to be the computer “brains” of the calculator. Up and to the left of that you can see a little metal clip that holds the battery to the board. Moving even more left, I found the symbols for a diode. There are two diodes, and one light emitting diode at the bottom left. I think the top two diodes are related to the solar cell mounted at the top of the device. To the right of the computer is what appears to be very tiny resistors, and even further right, a capacitor. Power to the LCD screen of the calculator is directed through the striped ribbon. The red and black wires attached the PCB lead up to the solar cells, above the LCD.

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Next, I simply dug a flathead under the corner of the face of the calculator and removed the silver lining (some type of aluminum foil) from the top of the device.

I then gently pried the PCB from its plastic mounting holes, and the little buttons began to slide out as the front face was removed from the PCB. You can see all the little circles on the front of the PCB correspond to a button, just like a keyboard. The little rubber mat below transfers the signal of your button press to the PCB. The little rubber domes on the mat have small electrical contacts under them that transmit the signal. The springiness of the rubber allow the buttons to be pushed back up once pressed.

 

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Next time I do something like this I think I would choose a more intricate and complex device. Something that moves under its own power would be very fun to dismantle. A calculator was fun though, and it’s cool to begin to understand what all the little components of a circuit do to make a device work. I was surprised to see how much solder was used on the board. I began to imagine how many individual pieces have to be soldered by hand, and then tested later on in production. Crazy! Thanks for reading.

Will Knowlton

 

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