DIY Christmas Decorations With the Kids

In this instructable we get into the festive spirit by designing some neat Christmas decorations with the little ones.

In this step we ask the kids to come up with a festive idea and give them some boundries i.e....

• No robots that talk
• No lasers
• No PCBs that are hard to draw
• Only 2 main colours please

We came up with some festive decorations.

In this step we come up with the design for the festive decorations. I use design spark to lay out my PCBs so the best bet is to avoid any curved edges and do designs that are based on polygons.

For the schematic I've just used CR2032 batteries and LEDs. Some points to note here on battery life. A CR2032 battery has approx 250mah capacity (3V to 2V). This means if our diode has a 2V forward voltage drop and requires 1mA the decoration will last 250/(1 * 24) = approx 10 days left on all the time. We can increase this by:

• Add 2 batteries in series to give us more voltage headroom (Wedging 2 CR2016's into the 2032 battery holder?).
• Add batteries in parallel or just specify a larger battery.
• Specify a larger series resistor to limit current e.g. in the above example R=V/I = (3V bat-2V Vfdiode)/1mA = 1KR. Doubling the resistance will make the LED less bright but last twice as long.
• Specifiy diodes with lower forward voltage drop that will last longer (the flickering white LEDs were poor in this regard).
• Taking the batteries out before we go to bed.

If you look at the battery discharge graphs you can see the batteries work best below 1mA draw. The LEDs chosen will have a big effect, the muticolored ones worked at 1.5V but the white flickering ones stopped working at 2.5V. Current consumption can be estimated or measured with a multimeter.

For the design there are a variety of online sites that allow you to get PCBs manufactured e.g.:

• Elecrow
• OSH-Park

Before that though it's worth uploading your designs to a site such as http://www.gerber-viewer.com/ to check the design is correct before sending them off to the PCB fab house. Your PCB design package will output designs as gerbers, you can zip these files to get them sent off for manufacture.

The BOM can be sourced off the internet:

• CR2032 and holder - ebay
• Flashy lights (work down to 1.5V) - Elecrow
• Flickering lights (that stop working at 2.5V) - ebay
• 1000R & 1500R resistors - ebay

Once all the bits have arrived (2-3wks) it's time to solder your designs together. Note - The feet and hooks I made by soldering lengths of wire to the PCB.