Logic Probe Schematic

Can someone explain the logic probe circuit functionality of each components in this schematic?

I’m a trying to figure out the functionality of this circuit like how it works:

http://www.pololu.com/picture/0J611.800.gif

I can’t tell you what every components is doing, there are a hundred.

From what I can see, it will detect logic high versus logic low and light the red or green light. The yellow light indicates either oscillation or a high pulse rate. The circuitry at top allows an audible output as opposed to the lights. The stuff at the bottom seems to be loads for the input signal.

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Homemade logic probe