1/8Bits On Our Mind 2005, Tim Kostka

Thomas de Colmar’s Arithmometer

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These gears indicate the input number. They are able to slide up and down through the 0-9 positions.

Here, the input number is 37.

Number Selectors

Number Selectors – Input Number

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The position of the number wheels indicate the output number. On the actual device, only one number would be visible—in the model, the frame is left open for visibility.

Here, the output number is 42.

Number Wheels

Number Wheels – Output Number

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Power Axle

The power axle transfers power to the step gears. It also keeps them in sync by turning them all at the same time and through the same axis.

Step Gears

Power Transmission

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Step Gear

Number Selector

Due to the design of the step gear, these two mating gears have a variable ratio.

Depending upon the input number, the step gear causes the number wheel to rotate up to 9 places. This is varied by sliding the mating gear to the appropriate position.

Step Gear Mechanism

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When the number wheel moves from 9 to 0, the carry mechanism is triggered.

A small protrusion on the bottom of the number wheel pushes the top carry slider into its engaged position. Although the is not much motion, it is enough to engage the carry tooth seen on the next slide.

Disengaged Position Engaged Position

Carry Mechanism Trigger

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When the carry mechanism is triggered, the carry tooth (blue) is lined up with the mating gear (yellow). When engaged, this advances the number wheel by one digit.

Disengaged Position Engaged Position

Carry Tooth Mechanism

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The locking mechanism is provided for reliability. It prevents the number wheel from rotating between turns of the wheel.

Here, it is in the locked position. When the step gear rotates enough, it will disengage.

Locking Mechanism

Locking Mechanism for Reliability