ATtiny-powered Christmas Tree

The goal of this project was to create a Christmas decoration that houses a secret puzzle. The implementation is based around the Microchip ATtiny25V at 1 MHz, which offers 5 GPIO pins with pin change interrupts. The board is driven by a single CR2032 battery and features a button for user input.

The MCU can be either programmed using the exposed connectors of the "tree trunk", or with an SOIC-8 clip. In my case, I opted for the latter. Details regarding the programmer can be found in this repository.

Modes of Operation

When we turn on the board, we can perform a quick check to see if the button is already being held down or not. If we encounter a normal power cycle, we enter christmas decoration mode. The button is now dedicated to cycling through different prebuilt light shows. If the button is being pressed at boot, we enter game mode instead. The game idea is inspired by Pop The Lock and Stop Me. To optimize flash usage, we emulate randomness by using a linear congruential generator as PRNG. At the end of each game, the board displays the total number of points using the "branch" LEDs: one left blink means +10, one right blink, +1. Using EEPROM flags, we can remember if the user surpassed a hard-coded points threshold in order to unlock secret light shows in the other mode.

BOM

Designator	Footprint	Quantity	Details
BT1	Renata_HU2032LF	1	Renata 701106 holder for CR2032
C1	402	1	Ceramic 100 nF
C2	402	1	Ceramic 10 uF
D1, D11, D3, D5, D7, D9	603	6	Osram LO L29K-J2L1-24-0-2-R18-Z
D10, D12, D2, D4, D6, D8	603	6	Osram LY L29K-H1K2-26-0-2-R18-Z
R1, R2, R3, R4	402	4	150 Ω
SW1	SW_Push_1P1T_NO_CK_KMR2	1	C&K KMR421NGLFS
SW3	SW_DPDT_CK_JS202011JCQN	1	C&K JS202011JCQN
U1	SOIC-8_5.3x5.3mm_P1.27mm	1	ATtiny25V-10SU

Photos

Image Licenses:

• Ball icons created by Good Ware - Flaticon
• Snowflake icons created by Good Ware - Flaticon
• Snowflake icons created by kmg design - Flaticon

Improvements?

If you have ideas for improvements, please don't hesitate to reach out! Since this is my first custom PCB project, advice would be highly appreciated! :D