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Christmas bauble decoration

A simple ornament powered by an Attiny85

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I wanted to create a simple but fun Christmas decoration, so I came up with this. It's derived from a flashing star that I made out of some perfboard (perhaps I'll post a picture of it some time.) I was originally going to make the PCB in the shape of a star, but that ending up looking like it would be quite tedious to do in KiCad, so a bauble it was!Special thanks to JLCPCB for making the first batch for me at no cost. www.jlcpcb.com.

The bauble features an attiny85, 5 LEDs (and their corresponding resistors), two holes to run a string/line/wire to hang it, and a spot to solder on a CR2032 holder.  

So far I've gotten sleep current down to 5.1uA and when an LED is on, max current consumption is around 8.5mA.  This is with a voltage of around 3 volts.  Doing some very back of the envelope calculations, it should easily be able to run off the CR2032 for a least a month.I did use some large SMD pads to create a very ghetto (but effective) footprint for an SMD CR2032 holder that I got off of lcsc.com (lcsc part number C70378.)

Some useful notes:

LED selection: I recommend using LEDs with forward voltages a bit below 3V if using a 3V power source such as a CR2032.  Red and green LEDs work well. I did try a blue LED which works ok on a fresh CR2032 but will likely dim a bit as the battery discharges. 

If one is planning to hang it, fishing line works well.

Using 0603 size LEDs instead of 0805 size ones works just fine. I found that I didn't have any 0805 size green LEDs but I had a few 0603 size ones and had little trouble soldering them on.

If one is planning to use the SMD CR2032 holder part that I mentioned earlier, the negative lead/pad is on the underside and doesn't extend past the housing, so it's not directly accessible by a soldering iron. My method for soldering this. Tin the lead and put some additional flux on it after it's tinned.  Put some additional solder on the negative pad on the PCB and add some additional flux afterwords.  Place the holder on the board, reflow the negative pad while holding the holder firmly against the board. After a few seconds, remove the soldering iron and allow it to cool. If all goes well it should be soldered.  Wiggling the holder gently should confirm that the lead/pad is soldered.  The positive lead/pad is thankfully isn't hidden under the housing, so it's a breeze to solder.

t85bauble_c.zip

Contains the source code and compiled hex file that rotates though all LEDs. Compatible with all board revisions. Recommended not using a CR2032 to power due to relatively high continuous current.

x-zip-compressed - 6.05 kB - 03/06/2020 at 19:02

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t85bauble1_1.zip

Contains the source files and compiled hex file that blinks an LED every 4 seconds and runs for about 30 minutes.

x-zip-compressed - 6.45 kB - 03/06/2020 at 18:59

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t85bauble1.1.zip

Includes the KiCad and Gerber files of the revision 1.1 board.

x-zip-compressed - 65.14 kB - 03/06/2020 at 18:42

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t85bauble1.1Gerbers.zip

Just contains the Gerber files of the revision 1.1 board

x-zip-compressed - 16.59 kB - 03/06/2020 at 18:41

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t85bauble_firmware.zip

contains both the source code and the compiled hex file for the attiny85

x-zip-compressed - 6.14 kB - 11/05/2019 at 23:37

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  • 1 × Bauble PCB
  • 5 × 0805 size LEDs recommend LEDs with a forward voltage below 3V
  • 5 × 0805 size 220 ohm resistors
  • 1 × 0805 size 10k ohm resistor
  • 1 × 0805 size .1uF capacitor

View all 8 components

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