Simple Design of RF Transmitter and Receiver Circuits

From short-range wireless control using regular IR LEDs to global HTTP control using the ESP8266, there are many ways to control something wirelessly. In this project, we will learn how to build wireless projects using 433 MHz RF modules. These modules are inexpensive and readily available due to their functionality. They can be used as standalone transmitters and receivers or connected to an MCU/MPU such as an Arduino or Raspberry Pi.

Here, we will learn the basics of RF modules and how to use them as standalone RF transmitters and receivers. Here, we explain RF transmitter and receiver circuits by using RF wireless control LEDs.

• 433 MHz RF transmitter and receiver
• HT12D decoder IC
• HT12E encoder IC
• Buttons (3)
• LED (3 pcs)
• 1M ohm, 47K ohm and 470 ohm resistors
• 7805 Voltage Regulator
• 9V batteries (2)
• Breadboard (2Nos)
• Connection cable

Before we get into the project, let me briefly introduce these RF modules. The term RF stands for "radio frequency" and the RF transceiver module will always work in pairs because it needs a transmitter and a receiver to send and receive data. The transmitter can only send information and the receiver can only receive information, so data can always be sent from one end to the other, not the other way around.

The transmitter module consists of three pins, Vcc, Din and ground, as shown above. the Vcc pin has a wide input voltage range of 3V to 12V. The transmitter draws a minimum current of 9mA and can go up to 40mA during transmission. the center pin is the data pin used to send the signal to be transmitted. The signal is then modulated using ASK (amplitude shift keying) and sent over the air at 433MHz. It can transmit data at a rate of about 10Kbps.

The receiver module has four pins, Vcc, Dout, linear output and ground, as shown above. the Vcc pin should be powered by a regulated 5V supply. The module operates at less than 5.5mA. the Dout and Linear out pins are shorted together to receive the 433Mhz signal from the air. This signal is then demodulated to obtain data and sent out through the data pins.

The RF module can also be operated without the encoder and decoder modules. Simply power both modules with the appropriate voltage as described above. However, this method has one big disadvantage. There can be only one button on the transmitter and only one output on the receiver. This does not help to build better projects, so we use the encoder and decoder modules.

As we know that the HT12D and HT12E are 4 data bit encoder and decoder modules, so we can make 16 different combinations of inputs and outputs. These are 18-pin ICs that can operate between 3V and 12V input supplies. As mentioned before, they have 4 data bits and 8 address bits which must be set identically on the encoder and decoder in order for them to work in pairs.

This diagram shows the complete circuit diagram for the project, including the transmitter and receiver sections.

RF transmitter circuit with a breadboard setup

As shown above, the RF transmitter circuit has the encoder IC and the RF receiver circuit includes the decoder IC. Since the transmitter does not need a stable 5V voltage, we use a 9V battery to power it directly. On the receiver side, we use the 7805 +5V regulator to regulate 5V from the 9V battery.

Note that address bits A0 to A7 on both the encoder and decoder ICs are grounded. This means that they are both stored at address 0b00000000. so that they both share the same address and they will act as a pair.

Data pins D8 to D11 are connected to the buttons on the encoder side and to the LEDs on the decoder side. when the buttons on the encoder side are pressed, the information will be transmitted to the decoder and the corresponding lights will be switched.

I have built the circuit on two separate breadboards, both powered by a separate 9V battery. After building them, it should look like the diagram below.

Power up both breadboards and you should notice that the LEDs will start to glow. Now press any button on the transmitter breadboard and the corresponding LED in the receiver circuit will turn off.

This is because the button pins (D8-D11) are internally pulled up by the encoder IC. Therefore, all three LEDs will be illuminated and when we press the button, the data pin is grounded, so the corresponding LED on the receiver side will turn off.