The project used 434 MHz RF Module which is capable of transmitting 4-bit data to a receiver. Thus, by pairing a single receiver with the transmitter, a maximum of four devices can be controlled remotely if they are directly connected to the receiver module without any other logic circuit between them. If some logic circuit or microcontroller based circuit is used at the receiver end, with a single receiver module maximum 16 devices (as 16 different signals can be sent in 4 bit data) can be controlled.
Fig. 1: RF Remote Control Prototype
In the project, LEDs are shown as loads. These LEDs are turned on/off using RF transmission. The LEDs can be replaced by any other load or device connected via a relay to the receiver circuit. The basic 434 MHz RF module configuration was used in the project. Learn about the basics of RF transmission and the basic RF transmitter and receiver model .
Required components
| REQUIRED COMPONENTS | NO. |
|---|---|
| RF transmitter and receiver module (434 MHz) | 1 |
| HT12E/HT12D encoder IC | 1 |
| LEADED | 1 |
| Resistor-10KΩ (quarter watt) | 8 |
| Resistor-1MΩ (quarter watt) | 1 |
| Battery – 9V | two |
| Test board | two |
| Push-to-on switches | 4 |
| Connecting wires |
Figure 2: RF Remote Control Block Diagram
Circuit Connections
The RF module circuit connections are the same as those made in the basic model configuration of the RF transmitter and receiver. In addition to the RF module configuration, four switches were connected to data pins 10 to 13 designated as D0 to D3 of the IC HT12E encoder. These push-to-on switches are connected via 10K ohm pull-up resistors. Address pins 1 to 8 of the encoder IC are connected to ground to assign the transmitter an address of 0x00. Pin 14 of the encoder IC, which is active low, is also connected to ground to enable uninterrupted transmission of the control signal to the RF receiver.
In the receiver module, the loads are connected to data pins 10 to 13 designated as D0 to D3 of the HT12D decoder IC. In the project, LEDs are used as loads and have a direct interface with the decoder IC. Therefore, maximum 4 LEDs/other loads can be controlled remotely using this project. The LEDs are connected in series with 1K ohm pull-up resistors to ground. Therefore, upon receiving a HIGH signal corresponding to a HIGH bit on that data pin, the respective LED starts to glow. When receiving a LOW signal corresponding to a LOW bit on that data pin, the respective LED stops shining. Similarly, if any other load had been connected to the data pins, it would have been turned on or off depending on the circuit configuration upon receiving the HIGH or LOW bit on the data pins. Address pins 1 to 8 of the HT12D decoder IC are connected to ground to correspond to address 0x00 of the RF transmitter.
Fig. 3: RF remote receiver prototype
Because the transmitter has been configured for uninterrupted transmission, any change in the status of the switches at the transmitter end immediately reflects a change in the on/off status of the LEDs or loads at the receiver end. Due to the latch-type nature of the data pins of the HT12D decoder IC, any change in the on/off status of the LEDs or loads remains persistent until a new signal with reverse bit status is received from the transmitter module. Consequently, pressing or turning off the switches on the transmitter module instantly turns the LEDs on or off, respectively.
How the circuit works
The RF module transmits 4-bit data as expected. By default, the HT12E encoder data pins receive a LOW signal, as they are grounded through 10K ohm resistors. Therefore, by default, LOW bits are transmitted and the same LOW bits are received on the data pins of the HT12D decoder IC and the LEDs remain off. Push-to-on switches are connected to data pins with the other terminal of each switch connected to the power supply. When a switch is pressed, the respective pin starts receiving a HIGH signal.
Since pin 14 of the IC encoder is connected to ground and the transmitter generates uninterrupted data transmission, when a HIGH signal is detected on a data pin of the IC encoder, a HIGH signal corresponding to that data bit is immediately transmitted and a The HIGH bit is decoded on the respective data pin of the HT12D decoder IC. When a HIGH signal is received on a data pin of the decoder IC, current starts flowing through the LED which is connected to the pin with a 1K ohm pull-up resistor in series with ground. Thus, the LED starts glowing when it receives a HIGH bit on the respective data pin of the decoder IC.
If the respective switch in the IC encoder is turned off, the corresponding data bit in the encoder is set to LOW again and a LOW bit is received in the respective data bit of the IC decoder. Thus, the LED connected to the respective data pin of the decoder IC is turned off again.
The experiment used LEDs as loads; however, any load can be connected to the data pins of the decoder IC. A load operating on AC current can also be interfaced to the receiver module using a relay connected to the data pin of the decoder IC through a transistor circuit. A maximum of four devices can be enabled or disabled with this project.
Circuit diagrams
| Circuit Diagram-RF-Remote Control |  |