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Simple christmas tree from 2 PCBs with pseudo-random blinkenlights. Soldering workshop subject.
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README.md

FaSTGLETree

Simple christmas tree from 2 PCBs with pseudo-random blinkenlights. Soldering workshop subject.

3D CAD rendering of an electronics-based christmas tree made from 2 PCBs slotted into each other to give it 3-dimensionality. There's a 3D printed star on top.

Features / Function

  • CR2023 coin cell for power
  • 1-pos SMD dip switch for on/off
  • button for manual shifting
  • 3 pin header with jumper for switching between timer and button for shifting
  • All ICs are low voltage (down to 2V / 2.5V) variants
    • 555 Timer set at ~.5Hz
    • SIPO 8 bit shift register for patterns
    • Pattern scrambling with 2x4 NAND gates
    • Feedback from 2 NANDs into shift register
  • 16 SMD LEDs connected to shift register and NAND outputs
  • 1 yellow THT LED always-on on top
    • Transparently 3D-printable star cap

Learn how to solder SMD:

See Slides (in German)

PCB Manufacturing

I usually order from JLC with the cheapest options, make sure to choose the manual placement of the order number (marker already included in Silkscreen)

Build instructions

Assembly Guides: Board A, Board B

  • It's recommended to make sure each PCB is in the best state it can be in first before combining them. Afterwards, soldering becomes more difficult.
  • For SMD parts, always solder a single pad/pin first before continuing to others
  • Pin 1 markings are the elongated silkscreen line and the dot/line on the IC
  • LED directions are not marked. The LED arrow should always point to the tree trunk/inwards (Anode to tip of branch)
  • There's no pattern to whether the LED or Resistor is on top on the LED branches. Always check the assembly guide!
  • J9 is usually not populated, it's left for external power
  • The THT LED atop should have its leads shortened to ~7-10mm
  • The THT LED atop is oriented using the flat side of its rim. The Flat side goes to the straight line, the round side to the rounded line
  • Keep in mind the Errata section below

Errata

  • [2022 version] There is a pull-up resistor missing for the button. A 10kOhm THT resistor can be soldered from the backside of the bin header to the battery holder.
  • [2022 and 2023 version] Be careful to not scratch the pcb surfaces with the legs of the top LED in order not to create a short circuit
  • [2024 version] There is a missing connection betreen R5 Pin 1 and +BATT. A bodge wire from R5 (outside) to the battery holder solder point is recommended. Otherwise, the push button functionality most likely does not work.

Cost

~10€ BOM @ 30pcs

Licensing

Licensed under CERN OHL, see LICENSE.txt