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Note: On a generic pcb the two photo transistors must solder together in opposite directions from one another. Look for the fat internal lead C  (collector) 

The phototransistors physically mount in the same direction on the etched pc board. 

You need a black plastic sleeve around the phototransistors to block the light coming from the sides. This will make the light exposure more directional toward the phototransistors front lenses . Thanks Newbie3

When constructing make certain the electrolytic capacitor negative side is faced away from the IC.

The power consumption of the circuit is extremely low. If you use this circuit to drive a mini amplified computer speaker input the optical circuits "AA" batteries would last years. Use the voltage divider below for a square wave through an amp. 

Line out can connect to a larger size speaker directly. If the TLC555 pin 3 output is fed into an amplifier input connect C2 10uf to a 10K resistor in series to a 1K resistor to ground, as a voltage divider. Take your signal from across the 1K resistor and ground. A CdS photo cell taken from a bathroom nightlight can be in series with this output line to the amplifier input used for a crude volume control.

Experiment: To modulate and drive a super bright LED then replace C2 with a 220 ohm 1/4 watt resistor and properly attach the +/- LED wires to the line out terminals. Pick up the sound remotely up to three feet away using a photo-transistor or a optical remote sensor. This also creates a volume control method.

A triangular waveform which creates a better tone (flute like) with odd harmonics is generated at pins 2 & 6 which is the top connection of C1 of the TLC555. This can be made useable by tapping off here and driving the high impedance input of an additional Op-Amp like a TL082 or high impedance amplifier input. This is needed for isolation of the triangular wave to avoid loading down the performance of the TLC555 circuit. A computer amplified speaker won't work properly here. Using the voltage divider a guitar amp here will give "some kind" of result.