Schema relay energized by darkness circuit schematic with explanation

Schema relay energized by darkness

Schema relay excited the night:

                                           . Figure 1: Diagram of darkness detector This circuit can be used to automatically turn the lighting of your car when you enter a tunnel or at dusk. It can also be used to turn on the lights in the garden at night and off in the morning at sunrise. As photosensitive element, we used a photoresistor (LDR) FR1 referenced in the schema.

Figure 2: Pinouts μA741

seen from above, the PNP transistor

2N3702 seen from below and

LDR (no bias).

Pin 3 (non-inverting) of the operational amplifier IC1 is connected to the junction of the LDR and R1 trimmer. The LDR is connected to +12 volts and the trimmer to the ground, the whole constitutes a bridge variable value. The opposite leg (inverting) of the operational amplifier is connected to the junction of the two resistors R2 and R3, R2 being connected +12 volts and R3 to ground, the whole constitutes a fixed-value bridge. The tenson the center is 6 volts. As long as the LDR is illuminated by a light on pin 3 of IC1, we have a positive voltage higher than the one on the bracket 2 and thus the output pin 6 of IC1 is at logic level 1 (+12 volts). R4 resistance therefore can not polarize the transistor is a PNP, the relay remains inactive. If the LDR is placed in the dark, the tab 3 IC1, we have a positive voltage lower than that present on the leg 2. Therefore, the output pin 6 of IC1 is at logic 0 (ground). The resistor R4 is grounded and the base of the transistor TR1 is biased (PNP). The latter then becomes conductive and the relay placed in its collector is enabled, which enables control of any load. The trimmer R1 connected in series with the photocell is used to assay the sensitivity of the detection. List of electronic components: R1 .......... 10 kW trimmer R2 .......... 10 kW .......... 10 kW R3 R4 .......... 1.2 kW R5 .......... 1.2 kW FR1 ...... ... Photoresistor C1 .......... 100 uF Electr olytique DS1 ........ Diode 1N4007 TR1 ......... PNP 2N3702IC1 ....... .. Integrated μA741 RL1 Relay ......... 12 V 1 RT