Is It Finally Time For Christmas Decorations?

Christmas tree PCB with Blinky Circuit

[Arnov] is trying to get into the holiday spirit and is doing so the way he knows how. He was thinking of some cool decorations for his Christmas tree and decided the best decorations are the ones you make yourself, so he made his own blinky Christmas tree ornament.

The famed “blinky circuit” is certainly one that we are no strangers to here at Hackaday. Some of our readers will be very pleased to see that he did in fact use a 555 timer and not an Arduino. The 555 timer is wired to drive the clock pin of the CD4017 decade counter and the outputs of the decade counter are wired to the LEDs. The LEDs are lit up sequentially upon each low to high transition of the clock pulse though you may try getting creative with your LED wiring scheme to achieve different blinking effects.

What readers might really take away from this build is [Arnov] detailing how to import images into his CAD tool of choice, OrCAD in his case. We know that can be a bit tricky sometimes. Finally, we love that this project doubles as PCB art and a soldering challenge. It would definitely make for a good demo project at your next beginner soldering workshop.

Cool project [Arnov!]

14 thoughts on “Is It Finally Time For Christmas Decorations?

  1. I don’t understand how he’s driving RGB LEDs with only two leads to each and a decade counter. They’re changing colors, and I can’t figure out how that would work. Even if there’s a controller IC of some nature in the LED, won’t it just lose power as the LED power is modulated?

    1. The schematic shows ordinary LEDs, and the 4017 only sets 1 of its 10 outputs high at any given time. As you say, I don’t see how it could look like the pictures. Only one LED would light at a time, and they would sequence in a fixed pattern.

      But I could imagine using RGB LEDs with built-in blinkers/sequencers, so as each one is selected, it self-cycles through its colors.

      Maybe the pictures have been doctored to make it look more impressive. Or, he using a different circuit than is shown on the page?

      1. I thought about the sequencing too, but the decade counter is going to turn the LED power completely on and off. When it’s turned off, the sequencer will forget its state, unless it’s nonvolatile, which I just can’t imagine. Maybe it is being flashed fast enough that the LED turns off, but gets turned back on before the sequencer completely discharges?

        As for using a different schematic, at this point in the video, you can see two traces going to each LED, but they’re changing colors. I feel like this is a magic part, but he just says “RGB LEDs” in the instructable.

        1. This circuit is.. odd…

          I’ve seen products using colour change RGBs where they time how long the LED has been powered, and then switch it off & on again to reset the colour (usually red).

          I could see this working if the 4017 was sinking current and the LEDs were commoned on the positive, that way one LED would always be off, and the 555 would turn a different one off every 15 seconds (555 freq as per schematic).

          Now this is how it seems to operate (in the video only 9 are lit), but this explanation and the schematic don’t match up, and the 4017 can’t sink (output only) current anyway.

          It’s a double “what?”; being the circuit can’t work, and why bother switching one off? Just have the LEDs and ditch the ICs.

      2. i think the LEDs are wired for active-LOW,
        if you look closely, you’ll see that one after another
        they switch OFF, that is, one is off, then relights as another switches off.
        they are not mechanically sequential on the “tree” for added effect;
        it looks random at first, but is a fixed ordering/placement.

        that being said,
        i have a simillar “self-animated” LED and substituted it for the HDD activity LED on my desktop.
        it sure DOES seem to remember where in it’s pattern it was,
        when the power was switched off (HDD not busy).

        it is VERY entertaining and provides years of useful fun,
        which must mean my particiular unit does NOT use flash or eeprom
        to remember where it was in it’s pattern/timing.
        This would have worn out ages ago if it were using true NV-mem,
        (older computer w. older HDD = more pulses and thus more nv-mem wear).
        So the effect-control must be CMOS,
        as an RGB LED with control-circuit does not have much room for capacitance.

    2. I made something like this thirty years ago, maybe as many as ten.

      But I used a hex schmidt trigger, cmis, each an oscillator. So a level of randomness. The circuit biard was a triangle, “Christmas tree shaped”.

      I guess there were white LEDs then, I remember a constant white one at the top. One or more were red/green, with three leads. So clocked from different oscillators, a level of changing color. I etched the oscillator, and places for the LEDs, but used wire to hook up the LEDs, I guess so I could rearrange things if necessary.

      I’d sort of forgotten about them, but a photo appeared last year, the most important one, and I actually included an ac adapter rather than 9v battery. I could retrofit it, change some to the sequencing rgb LEDs. Maybe some of the newfangled types now available.

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