Procedure:
Transmitter Section:
Step 1: connect the LDR to data input pin 11 of the HT12E, with 10 KΩ pull up resistors.
Step 2: connect the 1MΩ resistor between 15 and 16 pins of the HT12E.
Step 3: Connect 17 pins to 2nd pin of RF transmitter and 14 pins connect to ground.
Step 4: 1-8 pins of HT12E are address pins, all connected to ground. Pin 18 is connected to Vcc and pin 9 is connected to ground.
Step 5: Connect RF Tx module pin 1 to ground, pin 3 to Vcc and pin 4 to antenna.
Receiver Section:
Step 1: Connect pin 11 of the decoder to the base of the transistor. Connect the transistor's collector to Vcc through the 10Kohm resistor and connect its emitter to ground.
Step 2: Pins 4,8 of IC555 timer are connected to Vcc and the 1st pin to ground.
Step 3: The 5th pin of IC555 is connected to ground through the 0.1uF capacitor and the 2nd pin is connected to the collector of the transistor.
Step 4: Short pins 6,7 of IC555 and connect to the junction of resistor (47K) and capacitor (0.1 uF) as shown.
Step 5: Connect the output pin (3rd) to the doorbell's positive terminal and connect the doorbell's negative terminal to ground.
Step 6: Connect the 50KΩ resistor between 15 and 16 pins of the HT12D.
Step 7: Connect pin 14 to the second pin of the RF Rx module and connect pin 17 to the LED indicator (it will glow when the signal is received)
Step 8: 1-8 pins of HT12D are address pins, all are connected to ground. Connect pin 18 to Vcc and pin 9 to ground.
Step 9: Connect RF Rx module pins 1, 6, 7 to ground, pins 4 and 5 to Vcc, and pin 8 to antenna.
Working:
1. The basic principle of this project is to trigger the timer IC555 to activate the buzzer when the LDR resistance becomes HIGH.
2. The resistance of the LDR changes depending on the light that falls on it. When the shadow falls on it, the resistance becomes high. Based on this phenomenon here we are activating the alarm.
3. In this project, this circuit is divided into two parts, LDR control on the transmitter side and buzzer control on the receiver side.
4. When the shadow falls on the LDR, its resistance increases, which changes the logic state at the input of the HT12E encoder. then it transmits this data serially to the receiver through the 434 MHz ASK Tx module
5. On the receiver side, the 434 MHz ASK Rx module receives this signal. Fits the HT12D decoder. The HT12D pin provides high output on the same pin connected to the alarm activation circuit.
6. Transistor receives high input, then conducts and provides low trigger input to IC555
7. IC555 generates high output pulse that buzzes for a few seconds. The time period depends on the connected RC components
8. The advantage of this design is that we can place the transmitter anywhere within range, and the number of alarms can be maintained with so many guards. With just one transmitter we can activate many receivers.
Photos:
While running the circuit, the following precautions must be taken
Precautions:
1. The status of the address lines (high/low) must be the same on the transmitter and receiver.
2. On the transmitter, the 14th pin of the HT12E must be connected to ground or connect a switch between ground and the 14th pin to reset the encoder.
3. In the transmitter circuit, the resistor connected between 15 and 16 pins of the HT12E must be between 750MΩ and 1MΩ. And on the receiver side, the resistor connected between 15 and 16 pins of the HT12D must be between 30KΩ and 50KΩ.
4. If you want to use any other battery, please check the HT12E/HT12D data sheet first.
Project source code
Project source code
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Circuit diagrams
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