This simple "Led Cube" circuit generates a random sequence without the use of microcontrollers. It uses a shift register in a configuration called Linear Feedback Shift Register ( LFSR ) .
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Step 1: 8 LED Cube at Work
You can arrange the LEDs in any any other configuration you like.
Step 2: Main Components:
IC1: CD4001 ( cmos quad nor gate )
IC2: CD4015 ( cmos dual 4 stage shift register )
IC3: CD4070 ( cmos quad XOR gate )
LED 1-8: any color, any size LEDs.
Step 3: 1 Mhz Oscillator, Shifts the Random Pattern.
Step 4: Differentiator Circuit
enables the 1Mhz oscillator for 150uS (150 microseconds)
Step 5: Linear Feedback Shift Register
This circuit generates random numbers. It is also often used to generate white noise ( a sea-wave type of sound ) which contains all audio frequencies in equal levels. Can be expanded by adding more stages.
Step 6: Multivibrator 1 - Sets the Pattern Change Rate.
Step 7: Anti-lock
If all stages are "0" the LFSR will lock in that state. These 2 components will prevent this by inserting a "1" into stage 1 if this happens.
Step 8: Led Outs
Leds are driven directly from CD4015 outs through current limiting resistors. Value is not critical.