This circuit uses the 4046 VCO/PLL IC, Voltage controlled oscillator and phase locked loop, and using this very versatile chip in its basic form to change frequency output (vco_out) when the input voltage changes (vco_in). These chips contain 3 main parts inside a phase detector comparator, a low pass filter(integrator) and a voltage controlled oscillator, whose frequency out is proportional to voltage in. The following circuit will represent the output frequency in terms of sound, these sounds will be varied by an LDR on Ledlabs board and two or three other varying signals R1 and R2 potentiometers. The phase locked loop will try to lock or maintain the frequency after comparisons of the two signals vi and vosc by the phase comparator, When a phase lock occurs, pin1 and pin2 outputs of the two comparators can be taken to a logic gate and a lock indicator /detector circuit could be attached, the output of these comparators on pin 1 and pin 2 of the cd4046, are a set of pulses whose widths are proportional to the difference between it’s two input signals, where pin 1 is normally high, and pin 2 is normally low, except for the pulses, the output current capability is low up to a couple of milliamps/pin on these outputs, (see data sheets) so from 5v with a red led a 4.7k should be okay to use, enough to see the pulsing.
phase difference is the difference, expressed in degrees or time, between two waves having the same frequency and referenced to the same point in time. Two oscillators with the same frequency and with no phase difference are said to be in phase. Two oscillators that have the same frequency but with different phases have a phase difference, and the oscillators are out of phase with each other.
The amount oscillators are out of phase with each other can be expressed in degrees from 0° to 360°, or in radians from 0 to 2π.
Sine waves and cosine waves could be the inputs which would be 90 degrees out of phase. or other harmonic waves 180 degrees out of phase(antiphase)(RLC).or other complex integer multiples of the fundamental frequency like odd/even harmonics, 2nd, 3rd, ….nth, which would require harmonic cancellation, not necessarily with this device.)
When a light dependent resistor is used as the input source some interesting sounds can be heard as these have a slow moving sort of signal, also another input at the same time can be used, like a triangle wave which will be generated on led labs board, (the input has a very high input impedance), the output will be fed in to an LM386 audio amp IC. and an 8 ohm speaker. This circuit is just a very basic use of the IC, for experimentation purposes, and normally on more serious circuits the output vco pin 4 would be tied to pin 3 phase comparators input, so it is not floating, as it can self oscillate and superimpose high frequency on the output signal of the vco at pin 4.
More complex things like Phase lags, integration of signals, complex sequential logic, signal conditioning, data synchronising, Harmonic wave forms etc is used here when fully understanding them and designing more complex stuff. Maths like the tuned circuit and calculus would be used Looking even further in to them. Music synthesisers started out with these types of devices.