This is an ornamental, if somewhat seasonal item that is in the shape of a star.

However, I wanted something different to the usual two-dimensional construction.

As a result, I created a three-dimensional version using three PCB’s.

One for the base and two shaped boards that when locked together form the 3D star.

Connections to the interlocked boards that form the star are made by pads that align with the control board and the two boards making up the star.

The two-star boards have LED’s on both sides and are therefore visible from any angle.

There are 3 LED’s on each side of the 4 arms for a total of 24 LED’s

In order not to detract from the overall form of the finished item and enabling visibility of the screen printing of a cubic form the LED’s are surface mounted versions.

The LED pattern can be changed by adjustment of the hex switch.

Additionally, flashing speed can be changed adjustment of the potentiometer that changes the oscillator frequency.

The star is powered by a 3V CR2032 which sits under the bottom of the control board, this is situated in the centre of the board and being flat allows the star to be free standing on a flat surface.

Power can also be supplied externally from a larger battery (I.e. 9V PP3), via the screw terminals or modified USB cable.

This is accomplished by the suitable positioning of a link on a header that selects the power source.

Holes are at the top of each arm to allow the star to be hung if required.

The double-sided PCB has been designed using EagleCAD and manufactured at OSH Park.

Circuit Description

The majority of the components are SMD, the exceptions being the timer frequency control resistor, the external power connector, the supply selection jumper and the supply polarity protection diode.

The circuit comprises an oscillator made from a 555 Timer (8 pin SOIC), whose frequency can be varied from a few hertz to a few hundred hertz. ~1.25Hz to 220Hz although the actual values will vary subject to component tolerances but are not critical.

The output of the timer is used to clock 3 dual D type Flip Flops (CD4013, 14pin SOIC), these are configured as a Linear Feedback Shift Register (LFSR), using an EXOR (CD4070), to provide feedback.

CD4070 truth table.

CLK

SET

RST

D

Q

LH

0

0

0

0

LH

0

0

1

1

HL

0

0

X

NC

X

0

1

X

0

X

1

0

X

1

X

1

1

X

1

LH = Low to High transition, HL = High to Low transition, X = Don’t care, NC = No change.

The Q outputs of each register are fed to the D inputs of each successive stage.

The first 4 registers have the R inputs connected to the HEX switch enabling them to be preloaded with a start pattern to pre-initialise the start sequence.

The S inputs of all the registers are connected together to enable the registers to be reset, using the reset button.

The remaining registers allow further randomness using links to connect the Q or /Q outputs to the next stage. The default links connect the fifth register Q output to the sixth registers D input and the sixth register /Q output to one of the EXOR inputs, completing the feedback loop.

Both outputs of the registers are each connected to an inverter (CD4069, 14 pin SOIC), with 2 LED’s connected to each of the 12 outputs.

Power consumption is dependant upon the supply voltage and the specific pattern.

However, guidelines of current consumption for the following voltages are listed.

3V = 3mA, CR2032 capacity can be between 210-240mAH meaning the battery will last 70-80hrs.

5V = 11mA

9V = 38mA