PCB Geneva Wheel

The classic Geneva Wheel mechanism, but sillier

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The Geneva drive is a classic way to convert continuous rotary motion into intermittent rotary motion. Usually, homemade demonstrations are done with 3d-printed parts, but I wanted to try incorporating a circuit.

The theory of operation is simple: An LED acts as the "pin" that pushes the slotted Geneva wheel along. Either a 5mm RGB LED, or a 3mm single-color LED for the proof-of-concept. A spacer underneath the Geneva wheel periodically closes or breaks a connection that then goes to the LED cathode(s).

Does it work? Nope! Well, not yet at least. I may try ordering the boards again, with no soldermask around the contacts. But I'm in no hurry.

Let me know if you have ideas or suggestions! Should I put little solder daubs on the exposed traces, or will that create high/low spots and make things worse?

  • Take Two

    Sam Ettinger02/17/2020 at 13:37 0 comments

    I'm going to order a new version of the spacer, driver, and base board. Here's what's changed:

    1. Thicker copper. I'm going with Oshpark's 2oz copper option. This means the boards themselves will be 0.8mm, but that's fine.
    2. Less soldermask. I've taken away the soldermask wherever the different PCBs come into contact with each other. I have no idea if this will help, but it can't hurt.
    3. More careful routing. There's a chance that the copper traces were creating high points and preventing contact on the prior revision. And I had to move most of the traces anyway, since I got rid of the soldermask.
    4. Better baseboard. Now it'll be easier to grip the base PCB and not have my fingers get in the way.
    5. "SMD" LED. On the driver PCB, I'm doing everything I can to keep the bottom side as flat as possible. That means no through-hole components. But I still want a through-hole LED as the "pin" on the driving wheel. So I'll fold the LED's legs over and solder it like a surface-mount part.

    Here's what hasn't changed:

    1. The Geneva wheel itself. I'll still be using the same ones from the first batch of PCBs. No need to order again.

    I haven't ordered yet, so it's not too late to suggest other changes or give advice on this version!

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morgan wrote 02/18/2020 at 17:02 point

Awesome! Way to get super weird with PCBs! I'm working through prototype of similar concepts (though I hadn't though of the Geneva wheel). One thing I'm absolutely loving in my designs are these 1.5mm spring contacts. They actual between 0.75-2.00mm making them perfect to sit between one spacer thickness of PCB.

  Are you sure? yes | no

Sam Ettinger wrote 02/18/2020 at 17:17 point

Wow, thanks! :D Those contacts would really come in handy!

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davedarko wrote 02/13/2020 at 15:38 point

you should ask @Drew Fustini from @oshpark for a coupon on Friday to try it again :D

  Are you sure? yes | no

Sam Ettinger wrote 02/13/2020 at 15:45 point

Oh that's right! I don't think he got a chance to see this in person yet!

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oshpark wrote 02/13/2020 at 17:35 point

Oh!  I saw this on Twitter but didn't realize it was you.  Yeah, definitely happy to give you coupons!  You'll be bringing it to xHain?  -Drew

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Ken Yap wrote 02/13/2020 at 13:40 point

Learnt a new term today, thanks. I see you don't have the elevated circular blocking disc that prevents the driven wheel from drifting in between steps. Will watch with interest.

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Sam Ettinger wrote 02/13/2020 at 13:55 point

Keen eye! I left indentations in the wheel so I can eventually add a blocking peg later down the line. Maybe I can make that out of LEDs, too, hehe.

  Are you sure? yes | no

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