As per our requirements if we want to implement any radio frequency (RF) technology basic project, we should start with 434 MHz RF transmitter (Tx) and Receiver (Rx) modules with RF encoder-decoder chips HT12E/HT12D. But in this basic project we are communicating with only one receiver, so we can control only one HT12D – means four data pins at HT12D. If we want to control more loads in same manner, means if we want to control number of receivers at a time and want to control several loads at a time then we should use multiple receiver circuits with only one transmitter. In this project we explained how to use multiple receivers with one transmitter.
The new approach in this project is, if same type of loads needs to be control at a time in same manner, by controlling number of receivers with one transmitter. By using only one transmitter we can switch ON/OFF several loads which are connected to number of receivers. We can send sensor data like temperature, humidity, LDR, to several receivers to make different type of applications.
As shown in above figure, in this project transmitter circuit consist of RF encoder chip HT12E and RF transmitter module. All address pins of HT12E are connected to ground. Receiver circuit consists of decoder chip HT12D and RF receiver module. Here also all address pins of HT12D are connected to ground. Several such receiver circuits we can use with same type of loads, but address pins of HT12D must be grounded.
Consider an example of an alarm system like smoke alarm or, intruder alarm, or fire alarm, where we can use this principle. The advantage of this principle is, we can sense with help of one transmitter but several alarms in different places within range will be activated. As per requirements the alarm system is small handy and portable so that it can be easily carried away anywhere and installed any where.
So the idea is clear now that, there is one transmitter that activates several receivers at a time. So let us see how it is done. First just gather required components and other equipments.
Required components and other equipments
1. RF Tx module (434Mhz).— 1
2. RF Rx module (434 MHz) – 2 (minimum) or more
3. HT12E – 1
4. HT12D – 2 (minimum) or more
5. LED — 10
6. Resistor – 1KΩ (Quarter watt). — 12
7. Resistor – 1MΩ (Quarter watt). — 1
8. Resistor – 50 K – 2
9. Battery – 9V — 3
10. Bread board. — 3
11. Pushbutton — 4
12. 8×1 DIP switches – 3
13. Resistor network 8×1@1K- 3
14. Connecting wires.
Follow the step by step procedure to build the circuit
Step1: connect the four push buttons to the data input pins (10,11,12,13) of HT12E, with pull down resistors (1KΩ).
Step2: connect 1MΩ resistor between 15 and 16 pins of HT12E.
Step3: connect 17 pin (Dout) to the 2nd pin of RF Tx module, and connect 14 pin (TE – Transmission Enable) to the ground.
Step4: 1-8 pins of HT12E are address pins, all are connected to ground through 8×1 DIP switch with pull down resistor network (8×1@1KΩ). 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 through 8×1 DIP switch with pull down resistor network (8×1@1KΩ). 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. When any push buttons is pressed on HT12E, it generates data sequence at 14th pin that is given to the 2nd pin of the transmitter module. Transmitted signal is ASK modulated signal with data in amplitude variations
2. At receiver side, received signal is given to 14th pin of decoder HT12D, from 2nd pin of receiver module. As an output, respective Led will glow on HT12D decoder output pins.
3. In this project we can understand importance of the address pins. This project uses two receiver circuits and one transmitter circuit.
4. To use transmitter as a universal transmitter , or to control all receiver circuits from one transmitter, address pins should be configure in one address mode at both transmitter and receiver side (means address pins status as high or low should be same at both side).
5. After configuring same address both side, if we send a signal from transmitter all receiver circuits will receive same data.
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.
Project Source Code
Project Source Code
Filed Under: Electronic Projects