R&D AND TECHNICAL SUPPORT ENGINEER
The modern wireless communication adventure, started by Marconi in 1897, continues to operate and develop today in the light of unabated needs and developing technology. RF Communication, one of the basics of wireless communication, is an abbreviation consisting of the initials of “Radio Frequency”. RF, one of the most commonly used methods in wireless communication, is used to offer wireless communication by sending signals from the transmitter to the receiver in a certain frequency range, using systems consisting of a receiver and a transmitter.
We know that TVs and telephones, which are the important technological devices of our lives, work with radio waves. The frequency range of radio waves is between 300 gigahertz (GHz) and 30 hertz (Hz). These values correspond to a wavelength range of 1 millimeter (mm) to 10,000 kilometers (km). 433Mhz RF in Short Distance Communication: We see that the 300Mhz – 433Mhz range is the most commonly used bandwidth in short distance communication. The RF module operating at a frequency of 433 MHz is one of the most widely used modules in our projects where short-distance communication is required. The RF module, which offers advantages with its affordable cost and simple use, provides a data transmission range of 70 to 80 meters in open areas (this distance decreases in closed areas depending on environmental conditions). Today, the 433 Mhz RF module is usually used in the fields of home security and building automation, industrial monitoring and control, wireless measurement and reading, wireless lighting and control, wireless alarm and security systems, as well as remote keyless entry applications.
Considerations for 433 Mhz RF Communication
• The antenna must have an impedance of 50 ohms.
• λ/4 Chip antenna length should be about 17.3cm for 433MHz.
• The antenna must be mounted upwards or downwards in an upright position to the module.
• The healthiest and most effective communication distance is achieved when the receiver and transmitter of the two modules see each other. Therefore, any object or metal obstacle negatively affects the communication distance.
• The microprocessor lines controlling the RF module are one of the noise sources. Therefore, the paths should be kept as short as possible.
• It is recommended to install an external regulator circuit for the RF module.
• It is recommended that the RF module be decoupled and fed to the processor via a different line from the main source.
Feeding the 433MHz RF Module
The supply voltage of 433 MHz modules is usually in the range of 5V-12V, and it is useful to use 12V for data transmission over longer distances. Also, when it works with 5V, it will draw a minimum current and can be conveniently used with a battery. On the other hand, and as mentioned above, you need to keep the battery voltage high if you install a regulator circuit in your module, which is important for the communication of the module. The reason we keep the battery voltage high is because a fluctuation in the source can negatively affect the healthy operation of the module.
CMT2210LH Low Power 300MHz to 480MHz OOK Receiver
CMT2210LH OOK demodulation (On-Off keying demodulation) offers low-cost high performance with our 300MHz-433MHz RF applications. The change of RF frequencies can be determined by the selection of crystals with different frequencies. It has the ability to operate in two voltage ranges, and depending on whether the “VDDL” pin is open or closed, it can operate in the range of 5.5V-3V and 2V-3.6V. It allows the user to use it easily with a battery with a current consumption of 4.5mA (433MHz).
Figure 1 shows the easy application scheme of the CMT2210 RF integration. (If R0= 0 ohm VDLL=1, the data output signal is read from the data pin as 5V, if VDDL=0, VDDL =3.3V.)
OOK Demodulation
As for On-Off Keying (or switching), the word keying/switching here is based on the Morse code in which it is turned on and off manually. OOK logically represents 1 and 0 respectively as the presence or absence of a carrier wave.
Figure 2 shows that the fields divided by time represent each bit.
Manchester Coding in RF Communication
We need to make the 1 and 0s that used for 433 MHz RF communication “meaningful”. The term “meaningful” here refers to the byte and bit concepts that we use in all our systems here. Manchester coding is used in binary data transmission, especially in analog, RF, optical, high-speed digital communication or long-range digital communication.
The basic idea in Manchester coding is that voltage “transitions” can be used instead of voltage “levels” to indicate the 1s and 0s. In Manchester coding, the falling edge of the voltage can be read as “0” and the rising edge as “1”. In order to better understand this, we see the standard digital interface consisting of the data signal and clock signal at the top of Figure 3. Just at the bottom of this, the version of this communication made with Manchester coding is shown.
As shown in Figure 3, the position of the data captured by the clock signal on the falling edge shows us that it is 1 and 0, while in Manchester encoding, we see 0 on the falling edge and 1 on the rising edge as the equivalent of this situation.
