When we are planning to control any load using RF (Radio Frequency) wireless technology, mostly in transmitter we prefer switches as control. But in some cases there may be need to use automatic switches like sensors. Consider an example of alarm systems, where load is to switch on or off motors. In such cases switches are not applicable. So we have to use sensors to activate actuators which are connected with receiver. Load may be any actuators, like motor, speaker etc.

 

The novelty in this project is, activating actuators (motor) wirelessly using remote sensor or an automatic switch. The advantage of this project is no need of human intervention to activate load, the sensor automatically detects input and activates the load.

 

 

In this project at transmitter side LDR’s are used as sensors (automatic switches). Also we can use here other sensors like smoke sensors, temperature sensors etc. LED’s are used as load at receiver side to understand activation of actuator. When LDR resistance changed from low to high, the LED turns ON to indicate actuator is activated. 

 

So let us start and see how this is done. First of all, collect following components and equipments.

 

 

Sr. no. Name of component Required quantity

 

1 RF Tx module(434Mhz) 1

2 RF Rx module(434Mhz) 1

3 HT12E   1

4 HT12D   1

5 LED 5

6 Resistor – 330Ω (Quarter watt) 4

7 Resistor – 1MΩ (Quarter watt) 1

8 Resistor – 50KΩ (Quarter watt) 1

9 LDR 4

10 Resistor – 10KΩ (Quarter watt) 4

11 Battery – 9V 2

12 Bread board 3

13 connecting wires

 

 

 

To build above circuit follow the step by step procedure

 

 

 

Step1:  connect the four LDR to the data input pins (10,11,12,13) of HT12E, with pull down resistors of 1 KΩ.

Step2: connect 1MΩ resistor between 15 and 16 pins of HT12E.

Step3: connect 17 pin to the 2nd pin of RF transmitter, and 14 pin connect to the ground.

Step4: 1-8 pins of HT12E are address pins, all are connected to ground. Pin 18 is connected to Vcc and pin 9 is connected to ground.

Step5: Connect RF Tx module’s pin 1 to the ground, pin 3 to the Vcc and pin 4 to the antenna.

 

 

Step1: Connect the four LED’s to the data output pins (10,11,12,13) of HT12D, with current limiting resistors.

Step2: Connect 50KΩ resistor between 15 and 16 pins of HT12D.

Step3: Connect pin 14 to the 2nd pin of RF Rx module, and connect pin 17 to the LED indicator (it will glow when signal is received) 

Step4: 1-8 pins of HT12D are address pins, all are connected to ground Connect pin 18 to Vcc and pin 9 to ground. 

Step5: Connect RF Rx module’s 1, 6, 7 pins to the ground, pins 4 & 5 to the Vcc and pin 8 to the antenna.

Now you are ready to run and test the circuit. Let us see how it works.

 

 

1. The HT12E encoder inputs are controlled by LDR’s, this parallel data converted by encoder in to serial data and fed to RF Tx module input pin 2 from the encoder 17th pin.

2. Transmitted data is ASK modulated signal. The data present in variations of the amplitude. The receiver within the range can receive the ASK signal and generates serial data same as at transmitter and fed to 14th pin of decoder (HT12D).

3. Generally LDR can be used in different ways, like a switch to detect high or low logic, or to sense the amount of light etc. In this project it is used just like a switch that turns ON/OFF based on light falls on it.

4. The respective LED at receiver side will turn ON when respective LDR resistance goes high (means when light is not falling on it)

 

 

 

 

 

 

 

 

 

 

Following are some of the points that may be useful to understand working of this project better.

 

 

1. Light dependent resistor operation principle: A light dependent resistor works on the principle of photo conductivity. Photo conductivity is an optical phenomenon in which the materials conductivity (Hence resistivity) reduces when light is absorbed by the material.

When light falls i.e. when the photons fall on the device, the electrons in the valence band of the semiconductor material are excited to the conduction band. These photons in the incident light should have energy greater than the band gap of the semiconductor material to make the electrons jump from the valence band to the conduction band. Hence when light having enough energy is incident on the device more & more electrons are excited to the conduction band which results in large number of charge carriers. The result of this process is more and more current starts flowing and hence it is said that the resistance of the device has decreased. This is the most common working principle of LDR

2. LDR can be connected in pull up or in pull down configuration, here LDR connected in pull up configuration. 

3. Pull up configuration: connect 10Kohms resistor one end to the Vcc another end to the LDR. LDR another end connected to the ground, the output taken at junction point.

In this configuration before LDR 10Kohms resistor drops some voltage and remains voltage is used by the LDR.

                                                                            

4. Pull down configuration: connect LDR one end to the Vcc another end to the 10Kohms. 10Kohms another end connected to the ground, the output taken at junction point. In this configuration based on resistance variations, it drops the voltage and remain voltage goes to 10Kohms.

                                                                    

When trying to design this project considerable point is pull down resistor selection. In this project I am using 10KΩ.

 

While running the circuit it is required to take following precautions

 

 

1. Address lines status (high/low) should be same at both transmitter and receiver.

2. At transmitter 14th pin of HT12E should be connect 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 HT12E should be between 750MΩ to 1MΩ.  And at receiver side the resistor connected between 15 and 16 pins of HT12D should be between 30KΩ to 50KΩ.

4. Incase if you want to use any other battery, checkout the data sheet of HT12E/HT12D first.