Glass PCB LED Clock

This clock looks fantastic because of the glass PCB used for the build. This banner image allows you to see all the traces and components, but when it is lifted off of the desk surface the LEDs which make up the 7-segment digits appear to be floating.

The concept isn’t new, but it’s a much larger format than we’ve seen before. When we first looked at [CNLohr’s] glass PCB fabrication he was using microscope slides. This uses a much larger pane of glass but it seems the fabrication still uses copper foil glued to the glass, then toner transfer etched like normal.

Here he’s testing out some 74LV164 chips as constant current drivers. One of the commenters on the Reddit thread is skeptical about using the chip in this way and so are we. But as the video after the break shows, it seems to work (at least for now). [CNLohr] also mentions that the AVR soldered on the display is burnt out which doesn’t help his case. Still, we love the look and can’t wait to see where he goes from here!

31 thoughts on “Glass PCB LED Clock

    1. Circa +/- 1970 or so ” that’s cock” was another term to mean cool far out sweet nice great sick etc, in some regions of the USA. I’m glad that died out because geeks would be linking to images of peckers, wasting a moment of time of others :(

      1. I was trying to embed it so people didn’t have to click on the link. So sorry I waisted 5 seconds of your time, that was very insensitive. Next time I’ll just say *puking rainbows.

    2. I was BS’n you and in general poking fun of the euphemisms used use to say we like something. My fault in not using an emoticon to denote the lack of seriousness of my intent, sorry

  1. The 74xx164 isn’t limiting current in any way. Its absolute maximum ratings, however, are 25mA sink/source for each pin and a total of 50mA going into or out of the chip. The highest current flows through these when displaying an “8”, so that makes it about 7mA before he exceeds those limits. Since he can regulate brightness by varying the voltage, there seems to be no constant current source in there at all.
    So, this obviously works for him and those particular ICs he has, but is neither 100% reproducible for everyone nor does he have a guarantee that the 164s will still work after a couple of weeks of operation.

    … Aaand i just found his comment on the youtube video, basically saying the same things i wrote ;-)

  2. Actually, 74lv164 datasheet gives a Voh about 4V for a 12mA Ioh. So the voltage is near the Vf of the led segments and they don’t burn. They’re voltage driven.

    If one of the led has a quite low Vf, there’s a risk of damage or simply a difference in luminosity.

    It has nothing to do with power sharing between outputs, it’s luck ^_^

  3. You can make a glass PCB using a mirror. The mirror stackup appears to be something like this:

    Copper Plating
    Silver plating

    I’ve used a laser cutter to etch away the paint on the back of a mirror, and then dipped the whole mirror into ferric chloride, I was trying to make cool non-silvered designs in the mirror. You could etch circuit traces this way as well.

    1. I initially tried to use angel gilded glass, originally with copper, but because the coating was so fragile, it would disintegrate whenever I tried soldering it, or even attempting to plate more copper on. I’d really like to see someone else try with a thicker coating.

  4. How much power does this use, I’m thinking this could be very artsy-fartsy if he combined this with a salt water battery in a glass “aquarium” setup. Nice work.

    1. This particular one? Tons! Actually, it’s out of spec for the LEDs even around 4V. You can still get LEDs to glow quite nicely with very little power, provided you can get them up to their Vf.

  5. How hard would this be to get to work on other substances, like acrylic, mdf, wood etc? The application of the foil would be OK, but etching would be a problem, so is there another way to remove the copper that could be used, like the light sensetive boards?

    1. I’ve tried a number of substances… There are really three things to consider with the material:

      1) Can you find a glue to glue it to copper? Epoxy many times does work, but can be frustrating to work with… Silicone sometimes works, too… Super glue has been a good one, but even with wood it seems to allow peeling.

      2) Will your material get stained by the ferric chloride. (actually most things are pretty robust)

      3) Can your material survive reflow? Materials like acrylic cannot, at all, survive the temperatures needed to solder parts. That’s one of the chief reasons I use glass. Silicone, Kapton and Glass are the big ones I use now.

        1. B270 from S.I. Howard Glass. They have a $100 minimum order. For smaller samples, you can just use some celestron microscope slides. I tried a few other glasses, none of them worked.

      1. Not sure what type that is. With glass, you’ve got to heat and cool slowly but borosilicate is pretty forgiving due to its low coefficient of expansion. wale aparatus might have cheaper boro sheets. You can also get tube or rod if you want to experiment with 3d shapes. I’ve yet to try but I’m pretty sure it will take the heat of an iron without cracking.

  6. Back in the early 90’s, I had a see-through pocket calculator. Everything except the LCD which hid the electronics was see-through, meaning that the traces were also transparent.

    Would it be possible to add transparent PCB traces to this design?

  7. I’ve wondered about making something like this only just gluing wire wrap wire onto the glass; Maybe some day I’ll try it out :) Less chemistry, could almost be as pretty as this but not necessarily.

    1. Unfortunately, I built this at a time in my life where I didn’t bother with schematics and skipped straight to the design. You can figure out the schematic pretty quick from the datasheets and layout.

      All that aside, I am designing a new version, and would not recommend (ab)using the 7400 series logic in the way I have.

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