There are different ways in which we can configure RF transmitter and RF receiver circuits for different applications.
First one is 434Mhz based one HT12E transmitter and one HT12D receiver without configuring address pins – in this RF transmitter circuit controls single device connected to RF receiver circuit so RF transmitter works as RF remote to operate device remotely
Second is one step advance. One transmitter is connected to many receivers at a time. In this case when transmitter sends the signal, all receivers within the range will respond at a time, here also it is not required to configure address. Consider an example of wireless call bell for schools/colleges/offices. In this system, the transmitter is with principal/boss receivers are installed in chambers of all staff members. When principal/boss wants to call staff meeting, he just presses button to call everyone and signal is transmitted to all receivers. industrial wireless intruder alarm system. In this system, if somebody enters in to the industry, alarm will activate, in this application transmitter is only one to detect and transmit but at a time several alarm system activate with that signal. Using this principle we can create many applications.
But this is not applicable when we want control several receivers each connected with different device/application using single transmitter at different time. Because here, all receivers activates at a time and respond to transmitter when it transmits. Consider an example in which using only one transmitter, one wants to control three different devices/applications connected with three different receivers like Rx1 with Ac motor, Rx2 with calling bell, and Rx3 with simple robot. Here he may not want to operate/control all devices simultaneously but first he will select the device to be control and then he will transmit signal
So this leads to selection/choice of receiver first and this can be done using address lines. All the receivers have different address line settings. When transmitter want to transmits to one particular receiver, it will first set the same address lines as receiver has and then transmit
For example, in office suppose the boss want to call an employee, so either he may call him directly, or he may call peon to call a person. Obviously, 1st option is better. But it requires intercom facility that is very costly. In small office it is not suitable also.
The economical solution to this is to use one transmitter with multiple receivers all with different address line settings. The transmitter is with the boss and different receivers are given to employees. When the boss wants to call one particular employee he will first select his name – means set address lines as per receiver and then he calls him. So only his receiver will respond and he will get the call.
Like this we can create many applications like, home appliances control using single RF remote called universal remote control. Using single remote control one can control switches/fans in all rooms, control different devices like AC, TV music system etc
The new approach in this project is, to control many different devices (loads) using only one transmitter. The transmitter controls several receivers individually, to control different loads that are connected to it. All the receiver have different address settings. The transmitter first sets the address and then transmits the data.
Each HT12E and HT12D has 8 address lines. Using these 8 address lines it can have 28 = 256 different address combinations. So there can be 256 HT12D receivers. Each HT12D has four data pins so if we connect each data pin to separate device then we can control up to 256*4 = 1024 devices.
As shown in above figure there are four receivers with following address pin settings
1) Address of Rx1 = 00000001 = 01h
2) Address of Rx2 = 00000010 = 02h
3) Address of Rx3 = 00000100 = 04h
4) Address of Rx4 = 00001000 = 08h
The address pins for transmitter can be set to 0 or 1 as per requirements. Now to control the device connected to Rx1 the address pins are set as 00000001. Similarly for Rx2, Rx3 and Rx4. Thus one transmitter can control total 16 devices connected to 4 different receivers.
So the idea is clear now that, there is one transmitter that can activate different receivers at a time only one. So let us see how it is done.
First just gather required components and other material.
Required components and other material
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 – 1MΩ (Quarter watt). — 1
7. Resistor – 50 K – 2
8. Resistor – 1 K – 12
9. Resistor network 8×1@1K – 3
10. Battery – 9V — 3
11. Bread board. — 3
12. Pushbutton — 4
13. 8×1 DIP switches – 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.
Step6: transmitter circuit connected in different address configuration by setting different DIP switches based on operation.
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.
Step6: the address setting is different in both receiver circuits.
Now you are ready to run and test the circuit. Let us see how it works.
1. When any push button is pressed at transmitter side, the encoder generates a data sequence at 14th pin,
2. It is fed to the 2nd pin of the RF Tx module. It transmits signal as ASK modulated signal with data in amplitude variations
3. At receiver, received signal is given to the 14th pin of decoder HT12D, from RF Rx module’s 2nd pin. As an output, respective Led will glow on HT12D decoder output pins.
4. In this project we can understand importance of the address pins. There are two receiver circuits and one transmitter circuit used in this project.
5. Two receivers are connected in different address modes, in Rx1 1st address pin active and in Rx2 2nd address pin active.
6. When we want to control load connected to Rx1 output, the transmitter’s 1st address pin must be active. Same as when we want to control load connected to Rx2 output, the transmitter’s 2nd address pin must be active
7. So by using one transmitter and just by changing its address pins configuration, we can control several receivers. At a time any one receiver is connected to transmitter depending upon address pin matching.
While running the circuit it is required to take following precautions
1. Address lines should be same at both side – transmitter and receiver (when you are selecting receivers).
2. At transmitter 14th pin 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/D first.
Here are few applications for this project
1. As a calling in any office, to call different employees using only one transmitter, without disturbing other members.
2. To activate different loads in industry with only one transmitter.
Project Source Code
Project Source Code
Filed Under: Electronic Projects