Automatic lighting control telephone signals

Diodes VD8 ~ VDI1, SCR vs composition control switch main circuit isolation diode VD7, stable orbital tube VD6, simple resistor capacitor C4 constitute buck regulator circuit,
Automatic lighting control telephone signals - schematic

the output DC voltage of about 24V for power control circuit. Sensitive electrical resistors and light-emitting diodes LED1 RGl constitute an optocoupler, it photoresistor RG2 and i diode VT group into a phone, light control circuit. Ll, L2 side in series with the telephone line, usually when no call between L1, L2 no current flows through the light emitting diode LED] no light, so photoresistor RGI exhibit a high resistance, the transistor VT cutoff, controllable silicon vs also turned off, the lamp H does not shine. At this time the entire circuit in a quiescent state, power consumption is minimal, less than found by ImA, can be considered not consume energy. When a telephone call is scored or off-hook dialing, between Ll, L2 current flows, the current telephone signal light-emitting diodes LED1 light, its light shines it presents a low resistance on the photosensitive resistor RGI. If during the day, because by the treasury within RG2 natural light irradiation also showed low resistance, it (RGl + RI) partial pressure of lower voltage generated thereon, not enough to make VT conduction, so during the day, although the phone, lights not light. Only at night, RG2 showed high resistance, the above share a high voltage, so the transistor VT conduction, C4 charge stored on the adoption of VT, VD5 rapid charge to C2, C2 charged to about 20V so that the left and right voltage. At the same time, C4 through the R3 vs SCR gate, between the cathode Yan electricity, so vs Xun said opening, electric lamp H lights up. Hang up after the call is finished, between L1, L2 no current flows through the transistor vT restore off, but the offer by R3 can continue to store charge in C2 vs gate current, so vs remain open state, L-what point lights remain bright light. Be C2 discharge end, vs loss of trigger current, ie when the AC zero crossing Tuen off, lights off.

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