4 Replies Latest reply on Jul 3, 2020 2:48 PM by BoTa_264741

    Simple FM audio transmitter using PSoC5



      This is a demo of the simple FM transmitter using PSoC5 (KIT-059). The project is very simple and uses no software code. AC input from the audio source is amplified (0-4V) and applied to the varactor diode, which controls frequency of the ceramic resonator (4.19 MHz). PSoC5 PLL is set to operate at 75.4MHz, which is 18x harmonic of the XTAL. It appears that PSoC5 internal PLL lock time is quite short (<250us), so that PLL can track the audio frequency (up to ~5kHz), though it less efficient at high range. Antenna is made from a 2" piece of wire, which is connected directly to the BUS_CLOCK output. There is no tank circuit, so transmitter emits on many harmonics of the main (1x, 3x, 5x...). Fortunately, 75MHz and 226MHz regions are empty, and emitted power is rather low (<100nW) so there is no issues with FCC.


      Any other ceramic resonator will work, the 4.19MHz is what i had at hands. PLL will lock to any XTAL with frequency >=4MHz. The varactor is also not specific, look for any which adjusts in 10-100pf in 0-4V range (hyperabrupt type). Since PLL feedback decreases with modulation frequency, adding simple CR high-pass filter at audio input with Fcutoff~1-4kHz improves FM output.


      RTL-SDR receiver dongle was used to receive the signal, and SDR# for visualization. See official website for details:



      Project archive is attached.

      Project uses the Annotation Library for connection diagram: Annotation library for CY8CKIT-059 Prototyping Kit


      YouTube video of transmitter action: PSoC5 FM audio transmitter (PSoC, PSoC5LP, PSoC 5) - YouTube





      Figure 1. KIT-059 connection diagram using Annotation Library for CY8KIT-059.




      Figure 2. Breadboard assembly (standard bredboard is split in two pieces).

      KIT-059_1c (1280x954).png

      Figure 3. RF receiver: RTL-SDR with short wire as an antenna.

      RTL-SDR_1a (1280x956).jpg

      Figure 4. RTL-SDR GUI (SDR#) snapshot at 75.581MHz.

      FM_SDR_1a (1280x720).jpg

        • 1. Re: Simple FM audio transmitter using PSoC5

          Hi ,

          I downloaded the program to try it. I tried to update the components. But nothing changed. I tried with Creator 4.2 and 4.3. Should I try  creator 3?

          • 2. Re: Simple FM audio transmitter using PSoC5


            The errors appear on the project annotation page, which is optional, and does not affect performance. The annotation page KIT-059 can be simply disabled or deleted.


            The errors arise due to Creator unable to find custom components from the old Annotation library v0.0, which is obsolete. If necessary, you can download and install it from the link above. New version of the PSoC Annotation Library v1.0 can be downloaded here

            PSoC Annotation Library v1.0


            Unfortunately, it is not compatible with previous version v0.0, and will show errors.

            If you want to see Annotation page, I suggest to add to dependencies old version of Annotation Library, but in the future switch to  a new version


            1 of 1 people found this helpful
            • 3. Re: Simple FM audio transmitter using PSoC5


              İt is ok. if I want to run it at 433Mhz. Can I just use saw resonator according to 433?

              • 4. Re: Simple FM audio transmitter using PSoC5


                The output produces multiple harmonics of the base frequency (in the above demo it is 75.4MHz), and I saw some signals in ~400MHz range also using RTLSDR dongle. You have to adjust PSoC bus_clk to match 433MHz.

                The resonator used above is ceramic type, 4.19MHz center frequency. It has wider bandwidth than quartz, and allows for about 1% tuning using varactor diode. Notet that PSoC can lock to resonator in the range between 4MHz to ~28MHz. I am not sure where the 433MHz SAW filter can be placed.