I know that it is now December but I still have one more Makevember project to include, which I mostly did in November, so I have made it a Makevember++ Project. It is just 7 white LEDs arranged in the abstract shape of a Christmas tree. I 3D printed a former to hold all the LEDs in place which was designed as an interference fit into a small wood frame canvas used for art. Unfortunately the wood frame I used for measurements is an older one I have already used and the newer ones, although the same outer size, have a larger inner size as they use less wood (persumably to save money). So instead of a good movement free interference fit there is no fit at all. So I just BlueTac'ed it in place. I might make a new 3D printed former as now there is probably room for a couple more LEDs. I considered using different coloured LEDs, to be more like the baubles on a Christmas tree, but they all had different brightnesses, different current levels and different on voltages. The whites looked nice so I just went with white.
I connected the LEDs up directly to the outputs of an Arduino Nano that Element14 sent me for an earlier Makevember project. The LEDs all have a common ground and are driven by a HIGH on a digital output pin. I did this as it means if the power voltage drops then all the LED voltages will drop equally so that the relative brightness levels will be maintained. It also means that If battery powered that as the voltages drop the LEDs will use less current and the life of the battery will be extended, albeit the LEDs will be dimmer. They are pretty bright now with a 1 kOhm series resistor so this should work for a while. I have not yet worked out the predicted life of the LED tree when using a specific battery set.