2B-LDR OPERATED SWITCH [WITHOUT RELAY AND TRANSFORMER]
The main attraction of this project is that no relay or power transformer is used in this project. The bulb gets lighted up as soon as it becomes dark. It goes into OFF position on getting the light. This project is used to put porch light or street light ON/OFF automatically.
LDR is the main part of this project. When light falls on it, its resistance become less and becomes more in dark. Through this project the porch light is made to put OFF automatically in the morning and put ON in the evening.
The popular timer IC NC555 is used as bi-stable multivibrator in the circuit. The pin no. 4 & 8 are given +ve supply. The pin no. 1 is grounded. LDR is connected between positive supply and pin no. 2. A preset VR2 [220KE] is connected between pin no. 2 & 6 and earth. The preset VR1 [220KE] is connected between pin no. 2 & 7. The pin no. 5 of the IC is grounded to a capacitor C1 [0.01mfd].
when Ldr is in dark the voltage at output pin no. 3 of IC NE555 becomes high. It goes to the gate of triac BE136 through resistance R1 [560E]. The triac is triggered and 100W bulb is ON. The preset VR2 is adjusted in a such a way that putting your hand on LDR the bulb is put ON. Preset VR1 is adjusted so that bulb goes OFF when LDR is kept in the dark. In this project LED [Red] glows in the day time and bulb is kept in OFF position. In night the bulb gets ON but the LED remains OFF.
While adjusting the preset light can be brought near LDR by a torch and to produce darkness hand is kept over the LDR. The phase wire of AC 230V supply in the circuit is given through R2 [10KE/10W] resistance and diode D1 [IN4007]. The nutral wire is grounded. The supply is kept at 12V by a zener.
PRECAUTION WHILE ASSEMBLING THE PROJECT
- Never touch the circuit with hand after giving AC supply.
- Identify the pins of triac and connect properly.
- Use IC base for the IC.
- Connect all parts after verification.