The project “IC 555 based Automatic Evening Lamp” is a simple and built around timer IC 555 and LDR. The bulb used in the circuit is turn on automatically in low light (evening) and turn off in morning.
Various other automatic night lamp circuit is already posted in betsengineeringprojects.com. Some are listed here, Automatic Night Lamp Circuit using TRIAC and SCR, Automatic night lamp using 7486 IC. The circuit posted here is standalone automatic evening lamp; simply you have to connect to mains supply and place where you want to use it.
Circuit Description of Automatic Evening Lamp
The circuit of IC 555 Based Automatic evening lamp is shown in figure 1. The circuit is designed using readily available component like timer IC 555, a LDR, and few other electronics components like resistors, capacitors, diode, transistor etc. For description we divide the entire circuit of IC 555 Based Automatic evening lamp into three main section i.e. power supply, control unit and switching unit.
Power Supply Unit: The power supply unit is designed using resistors, capacitors and diodes as shown in circuit diagram. Here we are using capacitor and resistor for voltage drop rather than conventional transformer. The use of transformer makes the circuit bulky and expensive. The two capacitors C1 and C2 used in this circuit is used to drop the mains voltage up to desire level where resistors R1 and R2 is used as current limiter which protect circuit from instant high current. Resistors R3 and R4 connected parallel to capacitor C1 and C2 respectively, the function of these resistors is to discharge the capacitor when power is off. The resistor prevent shock due to energy stored in capacitor.
The low voltage output of capacitor C1 and C2 further need to change to DC voltage. For changing AC to DC we had used bridge rectifier built around four general purpose rectifier diode (1N4007). This rectified output is filtered using capacitor C3 in order to make ripple free DC output. The working status of power supply unit is indicated by LED1 where a resistor R5 is current limiter resistor which protect LED from burning out.
Control Unit: The control unit of IC 555 Based Automatic evening lamp is designed using timer IC 555 and LDR. The timer IC 555 is configured in bi-stable mode. The trigger pin (pin 2) and threshold pin (pin 6) is stored which is further connected to output of LDR as shown in circuit diagram. You can also adjust the sensitivity of LDR by replacing R6 with 1 M variable resistor. The threshold and trigger of IC1 is controlled by LDR and a 470 (R6) resistor. When LDR1 offer low resistance (Day time) the threshold of IC 555 become high as a reset the internal flipflop reset and output become low. Similarly, when LDR1 offer high resistance the threshold of IC 555 becomes low as a result the internal flip fop sets and output become high. The output of IC1 is available at pin 3.
Switching Circuit: The switching circuit is designed using a 5V relay and a transmitter. When the output of IC1 is high transmitter T1 start to conduct as a result the relay energized. The energized relay RL1 switch on the Bulb B1 till the resistor of LDR become low. Similarly, when the output of IC1 become low, transistor T1 goes into cut-off region as a result the relay connected to collects de-energized and Bulb B1 get switched off.
PARTS LIST OF IC 555 BASED AUTOMATIC EVENING LAMP
|Resistors (all ¼-watt, ± 5% Carbon)|
|R1, R2 = 220 Ω, 1W
R3, R4, R6 = 470 KΩ
R5, R7, R8 = 1 KΩ
|C1, C2 = 1 µF, 400V (Polypropylene Film Capacitor)
C3 = 470 µF, 16V (Electrolytic Capacitor)
C4 = 10nF (Ceramic Capacitor)
C5 = 10 µF,16V (Electrolytic Capacitor)
|IC1 = NE555 (Timer IC)
T1 = BC547 (NPN Transistor)
D1 – D5 = 1N4007 (General Purpose Rectifier Diode)
LED1, LED2 = 5mm any color LED
|RL1 = 5V Relay
B1 = 230V, 60W AC bulb
LDR1 = Light Dependent Resistor