White Noise Source
24 Stage Linear Feedback Shift Register (LFSR)
This circuit can be used to generate a pseudo-random sequence of
0's and 1's -- that is "white noise" or "static." The schematic shows a
24 stage shift register with XNOR taps at registers 7, 16, 22, and 24
using the Fibonacci configuration.
With these taps, the circuit generates a "maximal length sequence" of
pseudo random values which
repeats only after (224 - 1) clock pulses.
This circuit runs off a regular 9V battery, a real advantage of CMOS logic.
Similar circuits can be constructed using the 4014 IC and/or using other
lengths and tap points. See my table for some
other configurations which use two or four taps.