Electronic Ruler Works Out Logic Truth Tables

Like [Brad], we’ve seen a number of PCB rulers out there. [Brad] was looking to take the idea and run with it. His DigiRule is a ruler with a logic gate simulator. What he built is a mash-up between PCB rulers, and the concept of electronic business cards.

All told it simulates seven logic gates, four flip-flops, and includes a four-bit counter. On one end of the ruler a CR1220 battery feeds the 18F43K20 which is performing the logic operations using buttons and LEDs. Of course the truth tables are printed on the back silk-screen, but playing with the lights is a lot more fun. We do find it fairly amusing that the centimeters on the bottom of the ruler are notated in binary.

It makes a lot more sense to hand out rulers than business cards; people might actually use them after you leave and you can still include contact info. This form-factor also breaks the mold. You can have a lot more space on a ruler and you’re not constrained by thickness (although [Limpkin] solved that problem). While we’re on the topic of business cards [ch00f’s] USB etch-a-sketch style card and this logic-based information delivery device top our favorites list.

[via Dangerous Prototypes]

23 thoughts on “Electronic Ruler Works Out Logic Truth Tables

  1. Looks really good. It would be great for beginners / students.

    The only thing that I would *try* to do differently would be to recess the the cell into the board and use a CR2016 or LIR2016 and perhaps a USB plug printed on the board for recharging.

  2. Hilarious the SI units are measured in binary since it is fundamentally a decimal system. Conventional Measure, OTOH is often binary or at least partially so. (1/2, 1/4, /18, 1/16…) (cups, pints, quarts, gallons, etc.)

    1. When he sets the flip flop to JK mode and both J and K as ‘1’ (equivalent to toggle) the toggle only occurs once per button press so there must be some de-bounce somewhere. Perhaps he is scanning the button slow enough that bounce isn’t an issue.

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