RF Modules are the commonly used wireless communication modules in embedded systems designs. The 434 MHz RF module is quite popular among many RF modules available in the market. Learn about the RF communication and basic setup of RF transmitter and receiver. These RF modules are capable of transmitting 4-bit data or a set of four control signals at a time. Actually, these modules transfer a 12-bit serial data of which 4 bits are dedicated to data and 8 bits are dedicated to the section's (Transmitter or Receiver) identification address. Any set of RF transmitter and receiver on the matching of their addresses can pair together. Therefore, it is possible to transmit data from a single RF transmitter to multiple RF receivers by just matching their identification addresses.
This feature of RF modules allows application of a universal transmitter section in two different ways. One case can be where same data or control signal has to be sent to multiple receivers. Like, the RF transmitter section is a sensor based system and on detecting a danger or request for call to action (Like buzzing an alarm), it transmits control signal to multiple alarms designed with the use of RF receiver sections. In this case, the transmitter section has to be configured to have a fixed address byte and all the RF receiver sections are configured to have that same address byte. This project is a demonstration of the same case.
The other case can be where the transmitter section is configured to have a variable address byte and multiple receiver sections are configured to have different fixed address bytes. The address byte of transmitter section is altered to transmit control signals to different receiver sections one at a time. In this case transmitter will be transmitting control signal or data to only one receiver out of many receivers at a time. Like a transmitter section might be used as a remote control and multiple RF receivers are circuited to a robotic system for controlling its multiple aspects. It is also possible that the transmitter section might be used as a universal remote control for controlling a group of robots.
Learn about controlling multiple receivers from a universal transmitter based on altering its address byte.
It is also possible to expand the operational range of RF modules by attaching an antenna of standard size to the RF transmitter and receiver sections and increasing the transmission power of the antenna. Learn about increasing operational range of RF module by using antenna and increasing power transmission. Increasing the operational range will make this project even more useful.
|Sr. No.||Name of the component||Qty. required|
|1||RF Tx module (434 Mhz)||1|
|2||RF Rx module (434 Mhz)||2|
|6||Resistor – 1KΩ (Quarter watt)||12|
|7||Resistor – 1MΩ (Quarter watt)||1|
|8||Resistor – 50KΩ (Quarter watt)||2|
|10||Battery - 9V||2|
|12||Connecting wires|| |
The project has one transmitter section and two receiver sections. The circuit connections of the transmitter are done as specified by the data sheets of RF transmitter and HT12E encoder IC. All the address bits of the encoder IC are hard-wired to ground so to have a fixed address byte of 0x00. The pin 14 of encoder IC is grounded to have an uninterrupted transmission so that as when request for a call-to-action is detected by a sensor, a nibble is transmitted immediately. In the circuit instead of interfacing actual sensor, push-to-on switches are connected at the data pins of HT12E. Pressing a switch will simulate the request for call-to-action in the circuit.
Both the receiver sections have the circuit connections as specified by the data sheets of RF receiver and HT12D IC. All the address bits of both the receiver sections are hard-wired to ground so that they have the same address 0x00 as that of the transmitter section. Since both the receiver sections have same address and same as that of the transmitter, they receive any control signal or data simultaneously. Instead of interfacing real actuators, LEDs are connected to the data pins of the HT12D decoder IC to simulate the call to action. The LEDs are connected to the data pins via pull-up resistors and ground, so on receiving a HIGH signal they should glow. When a control signal (HIGH bit) is transmitted at a data pin of HT12E, the LEDs connected to the corresponding data pins at HT12D IC(s) also receive a HIGH bit.
How the circuit works?
The address byte of transmitter section is hard-wired fixed to 0x00. The address bits of both the receiver sections are also hard-wired to 0x00. Therefore, when a control signal or data is transmitted by the transmitter, it is received by both the receiver sections at the same time. The transmission of the signal is uninterrupted as the pin 14 of encoder IC of the universal transmitter section is hard-wired to ground. By default, the data pins of the encoder IC are connected to ground and receive LOW bit. Thus a signal of 0x0 is transmitted to the RF receivers every time.
When a switch is pressed, the bit at the respective data pin becomes HIGH. The new nibble is transmitted to and received by both the receiver sections due to address byte matching. Thereof, the respective data bits at the decoder ICs of both the sections become HIGH. The LEDs are connected to the data pins through ground. On receiving a HIGH bit at the respective data bit(s) of the decoder ICs, the respective LEDs get forward biased and starts glowing.
Since, the data pins of the decoder ICs are of latch-type once a signal is received it remains persistent until a new signal is received with the status of the respective data bit changed. This ensures a real-time call to action where call to action remains activated until request for the call to action is terminated from the transmitter side. The call to action (like buzzing an alarm) is terminated when the alternative control signal (LOW bit in this circuit) is transmitted from the transmitter module.