Larson scanner using 7400 series logic hardware

[RandomTask] is sharing a Larson scanner he built a few decades ago. These days you can whip one of these up using an Arduino in under an hour. He mentions this, but we agree that for nostalgic purposes there’s nothing like implementing the scanning LED effect using hardware.

Often called a Cylon Eye (after the television show Battlestar Gallactica) or referred to as the lights on the front of Kitt (the car from Knight Rider), the effect doesn’t just involve switching LEDs on and off in the proper order. A true Larson Scanner fades the LEDs as the bright point moves away from them, resulting in a tail that dims over time.

This implementation uses a 555 timer as the clock signal, allowing for speed control through a potentiometer. A counter chip, J-K flipflop, and line decoder all work with each other to address the movement of the brightest light. The fading effect is managed via a capacitor and resistor for each LED. The video after the break shows the pleasing result of this setup.


  1. Hirudinea says:

    Ah, isn’t that cute, a baby cylon.

  2. fdawg4l says:


    Cylons can’t have babies. N00b.

  3. Frack 'em all says:


    Yes, they can. A major story arc in BSG involved the baby of one of the Valeri (“Boomer”) model.

    One should always be courteous, but if you choose not to be at least check your facts first. There is no justification for being both rude and ignorant at the same time.

  4. Whatnot says:

    BTW, I wonder if there’s so subconscious sexual appeal to that light effect.
    What do you think?

  5. At first I was like, what’s so special? But really it’s VERY NICE because they integrated the FADING IN/OUT of the LEDs to simulate the same effect incandescent bulbs produce. I designed essentially the same circuit using a 555 and a 4017 a few weeks ago. Simple yet effective. +1!

  6. Effigy says:

    nice except fade out does not appear to adapt to the “swing” timing, meaning the faster it goes the less contrast there is… looks kinda not right to me…

  7. Graeme says:


    In Knight Rider they sped up (or slowed down) the recording to make it seem like the car was going uber fast. The bulbs only seem to fade quicker. The same effect can be achieved with this setup.

  8. GaryC says:

    i made one 10 years ago using a 555 and a 4017.

    Larson Scanner

    Very simple compared to this one ;-)

  9. Mattster says:

    Brings back memories of my younger years in 1985 at New England Tech

  10. HackerK says:

    Oh good old analog electronics and TTL/CMOS days…

  11. Destate9 says:

    Bro, this is so chill. I made one of these last year as a prop for my school’s play (with a 555 and 4017), but I’ve thought about making a “Tron-like helmet” with these

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