Viewing blog entries in category: FM Transmitter
An FM transmitter is one of the most popular devices between electronic hobbyist, professionals and even non-technical people. In this article, we gonna learn to how to build an easy, stable and digitally controllable FM transmitter.
For this design, I have selected the VMR6512 module which truly is like a full RF block on a chip!. It eliminates all essential circuitry for a basic FM transmitter such as inductors and trimmers. According to the VMR6512 datasheet: “VMR6512 is a highly integrated FM audio signal transmitter module. It integrates advanced digital signal processor (DSP), frequency synthesizer、RF power amplifier and matching network. So it can realize FM audio modulation without any external components. VMR6512 can also achieve broadcast quality sound by using digital pre-emphasis, digital filtering, automatic gain control, and digital frequency control technologies.“
The operation frequency range is between 88.0MHz to 108.0MHz. the figure-1 shows the schematic diagram of the transmitter.
Figure-1, The schematic diagram of the FM transmitter
The LED D1 shows a proper power supply connection to the circuit(3.3V). The capacitors C1 and C2 reduce the supply noise (0805 packages). Three tactile switches (push button) have been used in the design. The SW1 resets the module, SW3 increases the frequency (+0.1MHz) and SW2 is used to decrease the frequency (-0.1MHz).
The figure-2 shows a view of the top layer and figure-3 shows a view of the bottom layer of the PCB board. The figure-4 shows a 3D view of the assembled board.
Figure-2, A view of the PCB’s top layer
Figure-3, A view of the PCB’s bottom layer
Figure-4, A 3D view of the assembled board
I used an SMA connector for the P2 (Antenna connection). Therefore you can either use it to connect an antenna or use it to connect the output to an RF amplifier. Before increasing the power of your transmitter, check the regulation and broadcasting rules of your country of residence.
You can download the Gerber and NC-Drill files from the reference.
Gerber and NC-Drill files: https://www.pcbway.com/blog/technol...l_less__100KHz_step_size__FM_transmitter.html
FM transmitters/receivers are one of the top favorite circuits of every electronic designer. An FM transmitter is one of the first circuits that an electronic enthusiast decides to build.
For this purpose, instead of using discrete components and building one of the traditional transmitter circuits, let’s use the Si4712/13 chip. According to the Si4712/13 datasheet: “The Si4712/13 is the industry's first 100% CMOS FM radio transmitter with an integrated receiver to measure received signal strength. The device leverages Silicon Labs’ highly successful and proven Si4700/01 FM receiver and offers unmatched integration and performance allowing FM transmit to be added to any portable device by using a single chip. The Si4713 supports the European Radio Data System (RDS) and the US Radio Broadcast Data System (RBDS) standards including all the symbol encoding, block synchronization, and error correction functions.”
The chip supply can be selected in a range between 2.7V to 5.5V. Therefore if you plan to connect it to a 3.3V microcontroller, you can supply the chip and design your circuit with the 3.3V supply, otherwise power it with a 5V supply to be applicable for the 5V logic microcontrollers. The connection interface of the chip with the output is the I2C. Therefore a proper supply voltage selection can prevent future problems with the logic voltage match, for example, a 3.3V microcontroller and the 5V I2C bus.
I use the Altium designer to design schematics and PCBs. I did not have the footprint or schematic symbol of the Si4712/13 chip, therefore, as usual, I used the Samacsys search engine to quickly find and use the component.
Anyway, I selected the 3.3V logic and prepared a basic schematic diagram. You can download and modify it based on your needs. If you have selected a 5V microcontroller, some small modifications should be made in the circuit, mainly to the I2C connection. I'll try to cover the logic level conversion in a different article.
A Si4712/13 Arduino library is also available which you can easily play with it and transmit the data. You can also measure the received signal strength.
“The Si4713 supports the European Radio Data System (RDS) and the US Radio Broadcast Data System (RBDS) standards including all the symbol encoding, block synchronization, and error correction functions. Using this feature, the Si4713 enables data such as artist name and song title to be transmitted to an RDS/RBDS receiver.”
We can make many cool projects out of this, isn’t it!