Vermes
Advanced Member level 4
It is a design of electronic Christmas tree. It consists of 72 transparent SMD LEDs in the following colors: green, red and blue. Diodes are connected in series by 3 diodes, and powered by +12V. They are turned on by transistors NPN-SMD in housing SOT323 (it is smaller than SOT23). The transistors are controlled from three shift registers 74HC595 (72 diodes are divided by 3=24 bits in three registers). The registers are powered from processor Atmega168. LEDs were placed in two PCBs (parts of the Christmas tree vertically put together forming a cross). You have to pass the signal between the parts of the Christmas tree, registers, etc. Both parts are soldered to a round base which is the PCB of LED driver with Atmega168. Its supply is taken from two pantographs on the bottom side of the PCB from the forth PCB which is placed under the round PCB.
The last PCB operation is based on microcontroller Atmega8 and is driven by unipolar stepper motor with small gear that spins the Christmas tree round.
Both PCBs can be controlled from a remote control, despite of the fact that each processor has its own IR receiver. A standard RC5 remote control is used for control.
Using that remote control allows you to:
- start/stop the stepper motor
- change right/left rotations
- increase/decrease speed
- switch any of 10 special effects from the processor's memory
- switch few statistical operating modes and mode of random lighting the lamps
- smoothly change the speed of flashing and the effect of pseudo-PWM
There is also a connector for Bluetooth module, which allows you to control the above functions from both the computer and mobile phone with operation system such as Android. You can create applications for these devices for better control.
After assembly, the PCBs were died with green spray and then finished with an artificial snow in spray. Standard wool was then put on the bottom as an imitation of snow.
The Christmas tree can operate showing changing effects by default with various speed. There is a great number of possibilities of creating the effects.
Schematic:
The effect of baubles can be obtained by covering all the SMD LEDs 1206 with a drop of hot glue. After drying, the glue looks wonderful as a bauble.
Video of operation:
Pictures of the construction. The LEDs can be brightened or dimmed – effect similar to multiplexing in shift registers.
Link to original thread (useful attachment) - Choinka elektroniczna - 2x ATmega,IR, krokowiec, 3x 74HC595