With Christmas around the corner I was thinking about a neat gift idea for my relatives and friends. I recently ordered a couple of pcb’s for a different project and I figured it would be fun to make Christmas cards from pcb. In addition to being a fun idea it’s also very practical. I design them once and then simply order them. So I went online to do a bit of research and came across this image which I then used as my primary inspiration.
Step 1: Designing the Circuit
I wanted to order my PCB’s at JLCPCB and in order to get their cheap fare the outline had to be within the 100x100mm range. I started by drawing an outline that fit my needs, which happened to be 100x70mm and then started designing.
I created a costume device in eagle which is simply a copper Pad that is 4mm in diameter to represent the dots at the end of the traces (which supposedly represent Christmas ornaments). In addition, I decided to include a couple of LEDs in the circuit. I mainly used nets in eagle to connect everything together. The LEDs are all connected in parallel to a subnet called VLED and each have one “ornament” attached. This subnet I is then connected to a resistor, which limits the current of the LEDs, and then to the main supply (VCC). The copper pads, or ornaments which are not paired with an LED are connected to another pad in pairs.
The procedure was always to place a pair of pads or a pad and an LED on the schematic and then directly arrange it on the board. I mainly stuck to the design from the image I found online but to the end I didn’t have enough room, so I had to improvise a bit. I just played around with the traces until I was happy with the design. The traces between the parts where drawn rather big in order to be visible on the finished product.
I also added a text on the bottom of the card. I initially just wanted it to say "Merry Christmas" or something similar, but I just didn't like the look of it. So I decided to go down the full nerd path and put a HEX code down there. Feel free to translate it into Ascii ;)
Here's the rather funky looking schematic:
The top side of the PCB:
And the bottom side of it:
I did pour a polygon over the entire bottom layer to connect all grounds to one another.
Step 2: Selecting Components
There are really only three different components to consider in this build:
- The LEDs -> should require as little power as possible but I still wanted through-hole components
- The resistor -> depends on the current I want to flow
- The power supply -> well obviously we need power from somewhere
My only limitations for the LEDs were that I needed to use 3mm through-hole ones since I designed my PCB with a 3mm footprint. In addition I wanted to minimize the power they need in order the increase the time the device can be operated. I settled for standard 3mm red LEDs which, at a voltage of 1.8V only drew around 2mA. With 13 LEDs in parallel this would equal a run time of about a day, which is more than enough for me since it's just meant as a Christmas card.
I also ordered some SMD cell mounts in order to not interfere with the pattern on the front of the pcb.
As I power source I decided to simply use a 3V button cell. I got some button cell batteries with a capacity of 620mAh.
I tested what current and voltage combination gave me a decent looking light and settled on, as stated above, 2mA at 1.8V. The button cell has a voltage of 3V which leaves me with 1.2V I need to burn on the resistor.
This time I did use an smd resistor a had lying around but you could just as well order one for very cheap.
Step 3: Assemblying and Finished Product
After ordering all the parts received them a view days later and started soldering all the components to the PCB. As you might have noticed there is no switch, so as soon as you insert the battery the card starts to light up.
I am actually quite happy with how it turned out, there are just a view things I would maybe make different if I ever create a second version of this
- Don't cover the traces in silkscreen. They are still very much visible but I think it would just look even better if the solder traces were also silver
- Add a tree outline as a silkscreen or even have them cut out the actual tree form
If you wish to create your own Christmas PCB feel free to download my eagle files and play around with them.
Thanks for reading and Happy X-mas!
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