These RF modules transfer 4-bit data at a rate of 1Kbps to 10 Kbps. Each nibble is transferred serially along with an 8-bit address of the transmitter. Any receiver module matching the address byte of the transmitter can receive data from the transmitter. Hence, it is possible to pair multiple receivers with a single transmitter.
Fig. 1: Prototype of Universal RF Transmitter for Multiple RF Receivers
If the transmitter and the receiver modules have common address, all receivers get the data simultaneously. It is possible that the receivers have different addresses and transmitter address is altered to transfer data to different receivers at different times. This project is a demonstration of the later case.
This kind of data transfer can be helpful where multiple units have to be controlled from a universal remote. For example, a robot may be performing multiple operations and control signals for those operations might be received using multiple RF receivers but from a single RF transmitter based remote control. Another situation can be where a group of robots or actuators have to be controlled in a fixed or random sequence and control signals are transferred through a universal RF based remote control.
This project has demonstrated the above stated functionality by controlling LEDs (instead of real actuators/robots/devices) connected to four different RF receivers from a single transmitter section. The transmitter section gets a variable address byte for pairing to different receivers at different times by using switches at the address bits of the transmitter’s encoder IC.
|Sr. No.||COMPONENTS REQUIRED||QTY.|
|1||RF Transmitter module (434 Mhz)||1|
|2||RF Receiver module (434 Mhz)||4|
|3||HT12E Encoder IC||1|
|4||HT12E Decoder IC||4|
|6||Resistor – 1MΩ (Quarter Watt)||1|
|7||Resistor – 50K||4|
|8||Resistor – 1K||18|
|9||Resistor network 8×1-1K||4|
|13||Switches (Push button)||4|
|14||8 x 1 DIP Switches||5|
Fig. 2: Block Diagram of Universal RF transmitter for Multiple RF Receivers
There are 4 receiver sections and one transmitter section in the circuit. The circuit connections of the transmitter section are made as specified by the data sheets of RF transmitter and HT12E encoder IC. There is however one modification in the circuit configuration of the transmitter section. The last four bits A4 to A7 of the address pins of the encoder IC are hard-wired to ground but first 4 bits A0 to A3 of the address pins of the encoder IC are connected to power supply via push-to-on switches. By default, the A0 to A3 address bits are connected to ground but when a switch is pressed, it receives power supply through the switch. By default, the transmitter has an address of 0x00 but it can be altered between 0x00 and 0x0A by pressing or releasing the push buttons. The pin 14 of the encoder IC is connected to ground to enable uninterrupted transmission of the radio signal. The antenna of 17.25 cm height is used at pin 4 of the RF transmitter to boast operational range of the module. Learn more about increasing operational range of RF module by using antenna and increasing the transmission power.
Fig. 3: Prototype of RF Receiver 1
The RF receiver sections are connected as specified by the data sheets of RF receiver and HT12D decoder IC. At receiver sections also, antennas of 17.25 cm are used. The data bits D0 toD3 of the decoder ICs in each section are connected to LEDs to get the visual hint of the received nibble. Each RF section is configured to have different addresses. In the first receiver module, A0 bit is hard-wired to VCC while all other address pins are connected to ground so that the receiver has an identification address of 0x01. In the second receiver module, A1 bit is hard-wired to VCC while all other address pins are connected to ground so that the receiver has an identification address of 0x02. In the third receiver module, A2 bit is hard-wired to VCC while all other address pins are connected to ground so that the receiver has an identification address of 0x04. In the fourth receiver module, A3 bit is hard-wired to VCC while all other address pins are connected to ground so that the receiver has an identification address of 0x08.
How the circuit works?
The circuit is connected like that the receiver modules have fixed addresses while the transmitter module’s address can be altered to pair with different receiver at different times. By default the transmitter has 0x00 address and it pairs with none of the receiver modules and the entire receiver modules by default have 0x0 data represented at the data pins of their decoder ICs. All the LEDs therefore, are in off state by default. The nibble to be transferred to the receiver modules can be set anywhere between 0x1 to 0xF to get at least one data bit at the receiver module HIGH and at least one respective LED to glow as indication of successful pairing of that receiver module to the transmitter. The data bits at the encoder IC of transmitter are set to 0x0 once again after successful testing with each receiver module. This ensures that only one receiver module is paired with the transmitter. Otherwise, latch-type nature of the data pins of the decoder IC can become a source of confusion.
Fig. 4: Prototype of RF Receiver 2
The pairing is first tested with the first receiver module. The nibble to be transferred is set between 0x1 to 0xF. The switch connected to the A0 address pin of encoder IC is pressed so the address of the transmitter is changed to 0x01. The first receiver module having the fixed address of 0x01 starts receiving the transferred nibble and LEDs start glowing according to the 4-bit data received. An LED connected to the data pin of decoder glows when a HIGH bit is received; alternatively, it remains in off state. On successful testing of pairing with the first receiver module, 0x0 nibble is transferred from the transmitter module by pressing off all the switches at the data pins of encoder IC. Consequently, all the LEDs connected to data pins of decoder IC also gets off.
Now, the switch connected to A0 address pin of transmitter’s encoder IC is pressed off and switch connected to A1 address pin is pressed down. The address byte of the transmitter is altered to 0x02. Now it pairs with the second receiver module having the fixed address of 0x02. The pairing with second receiver module is again tested by transferring a nibble between 0x1 to 0xF and on test success, 0x0 nibble is transferred to terminate test.
The pairing with third and fourth receiver module is also tested similarly by modifying the address byte of transmitter to 0x04 and 0x08 respectively. The same process of first transferring a nibble between 0x1 and 0xF, then on test success transferring 0x0 nibble is followed. This completes the demonstration of pairing of a universal RF transmitter with multiple RF receivers by changing the address configuration of the RF transmitter.