Today, in this article we are going to taught you how to make automatic fence lighting circuit with alarm using op-amp 741 and timer IC 555. Basically, fence lighting is used for security purpose and can be used at various place like door alarm, pathway alarm etc. where monitoring is required.
Various types of fence lighting circuit are already available over internet but the problem with those circuit is they required high precision alignment. In order to overcome this problem, we had designed a very sensitive automatic fence lighting circuit. We had not used any inbuilt light source, you can place this circuit within the line-of-sight to any light source like sunlight, electric light etc.
Circuit Description of Automatic Fence Lighting Circuit
The circuit of automatic fence lighting circuit is shown in figure 1. The construction of this project is very simple and is built around readily available electronics components like op-amp 741, timer IC 555, PNP transistor BC557, LED, piezo buzzer and few other passive components like resistor and capacitors.
IC741 is configured in voltage comparator mode where resistor R1 and R2 is voltage divider which provide reference voltage and LDR with variable resistor RV1 is also voltage divider and provide signal voltage. Timer IC 555 is configuring in monostable multivibrator mode where resistor r6 and capacitor C2 is responsible for time delay because these two components are called time constant.
Basically, a voltage comparator compares a signal voltage on one input of op-amp with a known voltage called reference voltage on the other input. This circuit is also called non-inverting comparator because Vin (input voltage signal) is given to non-inverting pin (pin 3).
Reference voltage of about ½ of 4.5V is available at inverting input (pin 2) and signal voltage to be compare is available at non-inverting input (pin 3) from the potential divider network build using LDR and VR1. The output may be high (+) and low (-) saturation voltage, depending on with input is the larger.
When Vin at pin 3 is greater than Vref at pin 2 then the output of IC1 will be high, which drive transistor T1 in off state. As a result, LED become off and IC2 is also stop from oscillation. Similarly, when light is interrupted on LDR, the voltage (Vin) at pin 3 is less than Vref voltage (voltage at pin 2) as a result the output of IC1 (741) become low. This low output trigger timer IC 555 (IC2) which activate piezo buzzer for definite time interval which is determined by resistor R6 and C2.
PARTS LIST OF AUTOMATIC FENCE LIGHTING CIRCUIT WITH ALARM
|Resistors (all ¼-watt, ± 5% Carbon)|
|R1, R2, R6 = 10 kΩ
R3, R4 = 1 kΩ
R5 = 470 Ω
RV1 = 50 kΩ (POT.)
|C1 = 0.01 µF (Ceramic Disc0
C2 = 10 µF, 16V (Electrolytic Capacitor0
|U1 = LM741 (Op-amp IC)
U2 = NE555 (Timer IC)
Q1 = BC557(General Purpose PNP transistor)
|B1 = 9V Battery
SW1 = Push-to-on Switch
PZ1 = Piezo Buzzer
D1 = 5mm RED Color LED
LDR1 = Light Dependent Resistor