This small appliance - low-frequency oscillator on the transistors T2 and T3 with the phototransistor T1, role which can perform any low-power transistor with remote cap. In the front wall of the case, against semiconductor plate phototransistor fastens collectively len. With the clamp the device fastens on the pocket jacket lens forward.
Light, reflected by the objects, focused by a lens and affects the phototransistor, changing its the flow resistance. When this oscillator frequency and the sound the phone is also changing. On key in the phone people who use this the device may to navigate in the environment its decor. As the transistor T2 can to use any germanium, reverse conductivity, with possible great h21e. As T3 is better use MP41, MP42.