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Component selection
The crystal diodes in the circuit are all NPN type silicon tubes except BG2 is a PNP type manifold. The penetration current of these diodes should be chosen as small as possible, and the B value should not be too small, and can be used at around 50. Speaker specifications are: 8 ohms, 0.4 watts, 2 inches. The light-emitting diode LED has an illuminating current of about 5 mA. Photoelectric tube D1 is model 3DU33, and can also be replaced by other types of photodiodes. The motor M is modified with a commercially available DC toy motor with a working voltage of 1.5 to 3 volts:
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