FM Transmitter Mod

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

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.

Could this be something more easily done with an ADA Fruit Playground express. If so, is there a resource on how to set this up maybe?

At that point are you doing much more than handling power from the MDK to the adafruit?  You'll end up with 2 development environments on two different processors, but at the moment cost isn't really a factor.  How do you plan on splitting responsibilities between the Playground and the MuC?

Actually it won't be necessary. The FM Xmitter and the Stereo decoder I think are the two main components in this equation. I need to figure out how to get the correct data outputs to the Stereo Decoder as well as the FM Xmitter. I know the I2S outputs from the MuC to the Stereo Decoder and the I2C outputs to the FM Xmitter. I need to check on How these are going to work. It's just a matter of studying NuttX backwards and front and figuring out how to write the software properly. I also need to figure out how to write a small Android app that can call functions specified in AdaFruit's interface for the two components.

https://learn.adafruit.com/adafruit-i2s-stereo-decoder-uda1334a/arduino-wiring-test

https://learn.adafruit.com/adafruit-si4713-fm-radio-transmitter-with-rds-rdbs-support/test-and-usage

So maybe if you could give me a hint as to how to implement this. I have completed the Blinky app by the way. So I am not a NuttX virgin. I have implemented that project successfully.

Just a very quick question I have about some of the pins.

I have the following pin outs to connect to the Stereo decoder.

I don't think that any of the SysCLK, Mute, DEEM, or PLL since they all have default values that are used.

However, the SP0, SP1 signals may need to be altered. They are automatically drawn low for I2S but may need to be altered for LSB Signals. I doubt that I will need this though.

I have the following pin outs to connect to the FM Transmitter:

This is my Current idea. I have looked at this in many ways, and I'm now trying to configure nuttx to work with the given ships on the board.

If you have any observations about this design, especially with regards to feasibility, PLEASE let me know.

Here are my sources for the information above.

https://learn.adafruit.com/adafruit-si4713-fm-radio-transmitter-with-rds-rdbs-support/pinouts

https://learn.adafruit.com/adafruit-i2s-stereo-decoder-uda1334a/pinouts

https://developer.motorola.com/documentation/mdk-overview

To be clear, you aren't routing the i2s signals to the MuC.  So you're not actually going to PC14, PC15, or PD7 on the MuC but instead are pretty much raw i2s lines that the Moto High Speed Bridge combines, and then expands back out on the Moto Z side.  That said, your pin selection makes sense, although the UDA1334A spec implies that SYSCLK is necessary.  Please note that pin 36 on the 80-pin connector can be used as a 19.2MHz output.  Not entirely sure what you're referring to with the SP0 and SP1.

PB10 and PB11 seem like good choices for talking i2c to the FM transmitter, it should be very easy to configure those pins as well as your reset output.

One final note would be that the MuC runs at 1.8V logic level.  You'll either need level shifters to bring it up to 3.3V, or you can use the Pi HAT Adapter which contains shifters to the 3.3V level.

So, from my understanding, the whole purpose of the stereo decoder is to receive I2S signals from the MuC. Not the other way around. For that reason, I thought those were the pins that allowed for Word Select, and the Back Clock, and The SDO to get the audio from the phone. Is it true that these pins are outputting this information for the process of decoding it into Left out and Right out for the FM Transmitter?

My goal is to take I2S to the Stereo Decoder.

This seems like the most complicated way ever to get FM transmission. You could just take an analog audio output (headphone jack?) and send it to an FM transmitter circuit. I2S may offer higher quality for a small portion of the system, but by the time it has been transmitted and received, and bear in mind most modern FM receivers are awful, the sound quality will be pretty average anyway. Analog input FM transmitters are available all over the place, unless I'm missing something..

Yes, I understand I can do that. I just wanted to build something that would work as a mod. This is just a project to get to know everything a little better.

You're very right. Just plugging into, or Bluetooth to an FM transmitter would be a lot easier. I am purposefully trying to do something more challenging.

I've decided to switch to using PC0 and PC1 for SDA and SCL. This corresponds more with the Audio Mod

I've decided to switch to using PC0 and PC1 for SDA and SCL. This corresponds more with the Audio Mod