PCB Christmas Ornaments

Client

Family, Friends, and those undecided

Location

Buffalo, NY

Resources

Year

2022

Design Files

The nostalgia and "je ne sais quoi" of Christmastime makes it a wonderful time of year. I strongly dislike, however, the culture of "buy, buy, buy" every consumer good and gift card that comes on a list, as it seems to alienate the gift from the giver, for reasons explored in "Abstract Work Alienates." It also adds an unnecessary burden of stress on individuals at a time when the pleasant enjoyment of kith and kin should be paramount.

While I might not give the snazziest or techiest gifts, I pour my entire creative self into them completely. When I give a gift, it's not the monetary price tag that gives it value, it's the creative effort and piece of myself that goes into the work. This particular instance is no exception.

Design Verification

This isn't nearly the most complicated design that I've done, but it is the design that had the highest stakes. I only had one shot at this PCB - not only was the manufacturing/assembly expensive, but the lead time of ~10-14 days meant that I could not reorder the design if the first revision failed.

I decided to use a simple transistor astable multivibrator circuit to achieve the effect of alternating blinking lights. I know this circuit well and I was confident that it would work and could be modified if necessary. I spiced my circuit to ensure that the theory worked, but the main concern was with component selection.

PCB Design & Assembly

I used JLCPCB's PCB fabrication and assembly services. While they have a long shipping time (~1 week) due to being a Chinese firm, I've used them in the past and they have unbelievably fast turnover times.

I had to use components from JLCPCB's component stock, as they do not allow customers to send parts, and sending parts would have slowed down their turnaround time anyways. The astable multivibrator circuit uses such simple components that I knew I could find the exact types and values I needed in JLC's library.

It's incredibly interesting to add the constraint of components that exist within a specific database. I had to carefully select components based on how much it would cost to assemble based on things like how many times the pick and place reel would have to be swapped. The hardest thing to find was two 180uF electrolytic capacitors that were in an SMT package.

The front design was the most important, as it's effectively the visual user interface. I used 12 red LEDs that would each flash with a 50% duty cycle, offset by 180 degrees - 6 on, 6 off. This makes for a nice light display but also prevents me from having to find a small battery that can supply 240mA without blowing up and burning down the tree on which this ornament will hang.

I also used 1 yellow SMT LED that is on constantly, mimicking a star.

I made sure to place only LEDs on this side of the board to declutter the visual field with other components.

Each LED resistor, astable multivibrator component, and the coin cell battery holder are all SMT, as mentioned above. I used very small component packages to keep a clean design, so I had all components professionally assembled except for the SPDT switch and the coin cell battery holder, which I assembled myself.

Of course, I included a quote from the best Christmas movie, "Christmas Vacation," on the bottom silkscreen, as well as a hole through which I passed a ribbon to hang the ornament on a tree.

I also added exposed copper pads that could be bridged together by solder in case my astable multivibrator circuit did not work for some reason. While the little lights wouldn't twinkle, a statically illuminated tree is better than a non-illuminated tree.

Testing & results

Thankfully, the boards worked exactly as I'd intended. I tied ribbons to them and packaged them up for giving.

The combined flashing red LEDs and the static yellow LED collectively draw a constant 140mA. The CR2032 coin cell batteries that I am using have a capacity of 240mAh, providing a runtime of a little over 90 minutes. I attached an extra battery to the back of each board to ensure that these ornaments can be used for many Christmases to come.