10 Replies Latest reply on Jan 17, 2018 7:56 PM by krobar14

    FM Transmitter Mod

    krobar14

      Hello,

       

      I am currently undertaking a project on my own. To develop a mod for my Moto Z Play.

       

      Just to give you some background into this. I tried implementing the PiFM GPIO project with the band pass filter feature recently on a raspberry pi. I expreienced great success with this endeavor, and thought that I would be able to do something similar for my Moto Z Play. I currently have all of the development tools, and the hardware, but I am just doing research, having implemented the Blinky Project already.

       

      I am currently reading through some of the Nuttx instructions, and purposes. The information given seems to show that the firmware contains the possibility for Audio signals being processed.

       

      What advice would you have for an Engineering student getting into this. I would like to have some input at where I should go from the Blinky project. I want to have a mod that takes my phone's audio, and sends it out over different FM frequencies. Is this even possible?

       

      Thanks!

      David

        • Re: FM Transmitter Mod
          motomodsdev

          Very possible, I recommend starting with the Audio Personality Card example.  This uses i2s to transfer digital audio from the Moto Z, and plays out a tiny mono speaker.  It should be extremely easy to rip this apart and stick on an FM transmitter.  Control of the transmitter, such as tuning, may be a different story.  If you use the Audio Personality Card, i2c/SPI/UART are more difficult to access.

          https://developer.motorola.com/build/examples/audio

           

          Once you've gained understanding, you may choose to build your own circuit on the perforated board (sounds like you're capable).  Or, take it to the next level and Partner with Moto to build and ship your Moto Mod!

           

          Please continue asking any questions you have along the way.

            • Re: FM Transmitter Mod
              krobar14

              I'm going to read through the schematics. I'm considering doing this for my Capstone class. I would need to have it done by April. Sounds like a nice challenge. No?

               

              Reading through the Internal schematics, I can see first that there is a TFA9890AUK. This is an audio amplifier. So If I can find a way to channel this, I might be able to utilize the software to amplify the signal.

               

              There are two metal knobs that connect to the speaker. I'm guessing this is some form of Audio output that is Analog. I would love for this to be so, since I would have a left and right output. Either or, I would be able to implement a radio transmitter.

               

              Still investigating the schematics. Hope to have it done by the end of the week.

              • Re: FM Transmitter Mod
                krobar14

                So a little background information of what I interpreted from circuit diagrams, and such.

                 

                The audio system seems to draw it's power from a TFA9890A module on the board. Drawing power from the system, in different forms there are power supply mechanisms it uses to do this. In the main schematics, Moto was kind enough to provide us with a BTB connector diagram, as well as a schematics for this power supply chain. I've attached both below.

                • Re: FM Transmitter Mod
                  krobar14

                  Just a side note, I am documenting everything for the purpose of better serving those in the Moto Mods community.

                  The Loudspeaker system contains the pin diagram fro this module. Just by researching it. I identified the two outpins that lead to the SPK_OUTA and SPK_OUTB. Not knowing what these were, I researched the technical paper on it and read it. Seems that there is an inverted output that is given off by this system. Normal being A and Inverted being B. I don't know if this will lead to anything, but I know that it's a start.

                   

                   

                  Notice the bottom right hand corner. The outputs line up with what is on the board itself. You can also identify power being drawn from the EE_PWR pin on the board and on the diagram. The correlation is easily identifiable.

                  • Re: FM Transmitter Mod
                    krobar14

                    Just another update. I've successfully read through the specification, and the hardware side of things. I have to look over the software, more specfiically the Audio MDK. If I can tweak this, with using an alternative Class-D Audio Amplifier, such as the TFA9890AUK, I can have an audio output that can be tweaked using another ADAFruit FM Transmitter. I've ordered both, but I still have to investigate the interface. I'll post on here once I find out more about these three things.

                  • Re: FM Transmitter Mod
                    krobar14

                    Will do. Thanks for your help. I'll post updates on this thread.

                     

                    Would another possibility be, building a GPIO board that would connect to the mod, and send out audio, the same way I did on the raspberry pi?

                    I'm more specifically referring to the PiFM Project on the raspberry pi.

                     

                    David

                    Raspberry Pi Radio Transmitter: 4 Steps

                      • Re: FM Transmitter Mod
                        motomodsdev

                        The MDK does generate clock and PWM outputs, so it appears it would be feasible to use the MuC in the same manner that they used the Pi.  In this case the audio would be an analog signal out of the TFA still, correct?  You would probably need to flywire a new circuit on the Perforated board, since the Audio card doesn't provide easy access to extra GPIO.

                         

                        If you run into issue configuring any MuC outputs, we're here to help.  As for how the user tunes the transmitter, than can be easily done with an Android app and pass the information to your Moto Mod using the Raw protocol.

                         

                        There's an interesting comment that this isn't really a good way to do FM since you "splash" out over other channels.  I thought your FM transmitter was a separate chip, controlled by i2c like the TFA is.  Pretty interesting just modulating a GPIO signal; not sure if that is easier or harder than a transmitter IC.

                         

                        Great documentation so far, really interesting to see this evolving!  But you confused me when you mentioned 2 knobs next to the speaker.