Street Light Circuit using LDR (Mini-project):Introduction:

In this mini project of street light circuit using LDR, we are going to operate street light using light dependent resistor (LDR).Objective:

The purpose of this mini project is to switch off the street light in the day and switch on the street light in the night.Components required:

Following are the components which we are going to use for this mini-project of street light circuit using LDR:

LDR (R1) Resistors : R2 = 100K, R3 = 1K, R4 = 1K Transistors: Q1 = BC 107, Q2 = SL100 K1 = SPDT relay 230V Lamp 9V battery Fuse (optional)

Description:

Following figure shows the circuit diagram of the street light controller using LDR. Here we have used a 230V lamp which will turn on in night and get turned off during day time.

Light dependent resistor i.e. LDR is the main component used in this mini-project. We know that the resistance of the LDR decreases as the intensity of the light increases and vice versa. Same principle is used here. When there is presence of light the resistance of LDR will be low. So the voltage drop across the pot R2 will be high, which keeps the transistor Q1 on. The collector of Q1 (BC107) is coupled to base of Q2(SL100). So Q2 will be OFF and so do the relay. The bulb will remain OFF.

Similarly at night the intensity of light decreases and resistance of LDR increases. Therefore the resistance of pot R2 decreases below 0.6V. This makes transistor Q1 OFF which in turn makes Q2 ON. The relay will be energized and the bulb will glow.

How to make a circuit of Automatic Street Light control system?

Automatic street light system is very common nowadays as it provides intelligent street lighting mechanism. It provides light automatically during night without any human interference. These energy saving street lights make use of incandescent lamps instead of LEDs.So here I will teach you how to make an electronic circuit for street light automation. The heart of this circuit is a LDR (Light Depended Resistor) which is connected as a potential divider with a 56K resistor. The drop across LDR is used for switching the transistor. Solar led street lighting systems are the advanced versions of this ordinary automatic street light controller.

1 Rectifier power supply (Step down transformer [1A], Diodes-4, Capacitor-470F) 2 LDR 3 Resistors (56K,100) 4 Transistor BC187 x 2 5 6V or 12V Relay 6 BulbWorking of Automatic Street Light circuit The bulb should remain OFF during daytime and turn ON automatically during night. The unique property of light depended resistor is utilized here. LDR is a variable resistor which has very low resistance in the presence of light and very high resistance in the absence of light. In this circuit, we create a potential divider network with an ordinary resistor in one arm and a LDR on the other arm. According to Ohms law (V=IR), voltage drop across the resistor increases when its resistance increases. Here the drop across LDR varies with changes in light intensity. That is voltage drop across the LDR is minimum in the presence of light and maximum in the absence of light. One end of the LDR is connected to the base of a BC 187 transistor. At night, the drop is very high (> 0.6V) and it is sufficient to turn on the transistor. When the first transistor is ON next one will also turn ON. Thus the relay coil energizes and the bulb will glow. During day time the drop is very small (< 0.6V), so the transistor remains in OFF state. The diode Df is the free wheeling diode used for decaying the energy stored in the relay coil when the circuit is switched off.