HifiBerry or alternative DAC for Dynamic_RDS

[TomasRa1]

On https://www.aliexpress.com/item/1005005393398013.html is possible to buy very cheap but with relatively good audio quality DAC for Rpi with IC PCM5102A.
It works nicely as good quality audio driver for FM transmitter as I tested.
For Rpi connection it needs these Rpi GPIOs: +5V/pin2, GND/pin6, BCK/pin12, LCK/pin35, Din/pin40
You can see on picture mutual connection and also 4 PCB jumpers, which must be soldered as on this picture:

For to use this or similar Rpi HifiBerry DAC or also for to use Rpi built-in PCM DAC we need reconnect Dynamic_RDS PWM output from pin32 (GPIO12) PWM0 to any other free pin, because built-in Rpi audio or external HifiBerry DAC needs this pin PWM0.
For more detailed informations regarding Rpi implementation of this HifiBerry DAC module, please visit eg. https://blog.himbeer.me/2018/12/27/how-to-connect-a-pcm5102-i2s-dac-to-your-raspberry-pi/.
I decided to use RPi pin11 (GPIO17) for PWM output.

It needs to modify "Dynamic_RDS_Engine.py".

1. Delete (or comment by "#") all regarding PWM0.
2. Added on the beginning of file to the end of IMPORT loads (from line 17):

~~~~~~
import smbus
import subprocess
import unicodedata
from time import sleep
from datetime import date, datetime, timedelta
from urllib.request import urlopen
from urllib.parse import quote
import RPi.GPIO as GPIO     # RPi GPIO for transmitter output power set
GPIO.setmode(GPIO.BCM)
GPIO.setup(17, GPIO.OUT)    # Set GPIO17/pin11 as PWM2 OUTPUT
pwm_2 = GPIO.PWM(17, 18000) # PWM2 set to GPIO17/pin11,PWMf=18kHz
pwm_2.start(0)              # PWM2 duty cycle=0 (0V on pin11)

@atexit.register
def cleanup():
  try:
    logging.debug('Cleaning up fifo')
    os.unlink(fifo_path)
  except:
    pass
  logging.info('Exiting')

# ===============
# Basic I2C Class
~~~~~~

3. Add under "class QN80xx(Transmitter):/def update(self):/# TX gain changes and input impedance" and above "def shutdown(self):"(from line 271):

    # TX output power update
    pwm_2.ChangeDutyCycle(int(config['DynRDSQN8066AmpPower']))
    logging.info('PWM2 duty cycle updated to {}%'.format(config['DynRDSQN8066AmpPower']))
    self.activePWM = True

4. Modify # With everything stopped, disable PWM (from line 279):

     # With everything stopped, disable PWM
    if self.activePWM:
      logging.debug('Stopping PWM2')
      pwm_2.ChangeDutyCycle(0)
      logging.debug('PWM2 duty cycle = 0')
      GPIO.cleanup()
      logging.debug('GPIO cleanup')
      self.activePWM = False

---

MODIFY Dynamic_RDS.php:

1. Delete or comment by "//" PWM0 detection on lines 97-99
2. Modify line 100 to: PrintSettingGroup("DynRDSPowerSettings", "", "", 1, "Dynamic_RDS", "DynRDSFastUpdate");
3. Modify end of file lines 116-124:

> <h2>PWM and audio hardware setup</h2>
> <div class="container-fluid settingsTable settingsGroupTable">
> For output power control of 
> Transmitter board: <li>Connect Transmitter board PWM input pin -> to RPi pin11 (GPIO17)</li> <li>Use ferrite bead around cable 
> between RPi and Transmitter board.</li> For HiFiBerry DAC: <li>Add line to /boot/config.txt:</li> <li>dtoverlay=hifiberry-dac</li> 
> <li>HiFiBerry/RPi connection: +5V/pin2, GND/pin6, BCK/pin12, LCK/pin35, Din/pin40</li> </div> </div>                                         
> <div class="container-fluid settingsTable settingsGroupTable">
> </div>
> </div>

---

MODIFY settings.json from line 115 (to 140):

>         "DynRDSQN8066ChipPower": {
>             "name": "DynRDSQN8066ChipPower",
>             "description": "Chip Power (92-122)",
>             "tip": "Adjust the power output from the transmitter chip",
>             "restart": 0,
>             "reboot": 0,
>             "type": "number",
>             "min": 92,
>             "max": 122,
>             "step": 1,
>             "suffix": "dB&mu;V <i class='fas fa-fw fa-bolt fa-nbsp ui-level-1'></i>",
>             "default": 120
> 	},
>         "DynRDSQN8066AmpPower": {
>             "name": "DynRDSQN8066AmpPower",
>             "description": "Amp Power (0-100)",
>             "tip": "Adjust the power output for the amplifier after the transmitter chip.",
>             "suffix": "% <i class='fas fa-fw fa-bolt fa-nbsp ui-level-1'></i>",
>             "restart": 0,
>             "reboot": 0,
>             "type": "number",
>             "min": 0,
>             "max": 100,
>             "step": 1,
>             "default": 0
> 	},

I am not so proffesional as Mr. Nick Anderson. I think that my code for Dynamic_RDS_Engine.py needs tunning, because I am only amateur. Eg. I was also not sucessful with attempt to not send PWM value repeatedly when not changed. But I tested this my solution in longer transmitter's operation sucessfuly.
I also think that when we will sucessful with improve i2c I/O errors during communication by replace SMBUS with "SOFTWARE I2C" than we can change all values setting on Plugin FPP web page to change for immediately update without need any restart (as I already realized above on PWM and chip power set).
I hope that Nick will be understanding :-)

[ShadowLight8]

Ability to switch which PWM is being used will be part of #27, but it is just the framework at the moment

[ShadowLight8]

I decided to keep #27 to be the basic enable/disable for PWM. I'll start a new pull request to allow changing which pins are being used for PWM and I2C.

[ShadowLight8]

@TomasRa1 I've had some time to read through all the info you posted. I've ordered, what looks like, the same I2S board so I have a way to test. (https://www.amazon.com/gp/product/B08SLPHY2Z/)

I did find https://forums.raspberrypi.com/viewtopic.php?t=220082 mentioned being able to use i2s and hardware pwm at the same time by moving pwm to Pin 32 / GPIO 12, so I'm going to give that a try first. That would allow the hardware pwm to still be used, just on a different pin.

I saw your use of RPi.GPIO so I looked into it more as an option for software PWM. That which lead me to https://pythonhosted.org/RPIO/. RPIO can do PWM by using DMA, so it's the middle ground between hardware PWM and software PWM. Something I can look into, especially if the hardware pwm pin change doesn't work.

I've started work on being able to change hardware PWM pins. It's up as a draft PR #28

[TomasRa1]

Thank you very much Nick!
HiFiBerry DAC needs these Rpi GPIOs: +5V/pin2, GND/pin6, BCK/pin12, LCK/pin35, Din/pin40. There are GPIO pins 18, 19, 21.
I would like to prefer configure any free pin for PWM, because it is universal at all cases.
Pin 11 (Gpio17) is located next to GND pin and it is thanks this position shielded from other i2c pins, which we use for Transmitter module and at the same time pin11 is next to these i2c pins, we can easy use flat 6pin connector for RPi and Transmitter interconnection. I think it is favorable to use pin11 for PWM.

It is also possible to update PWM value dynamically in time, we do not need restart FPPD or any reboot for to change PWM value (the same as power of TX chip 8066). I changed Dynamic_RDS.php and settings.json source files (as I already described here above) for this dynamic set of PWM value. And also tested OK.

[ShadowLight8]

I've got the hardware PWM pin selection done in #28
Next, I'll follow your idea and make the PWM value dynamic so restarts are not needed.
After that, I'll start looking into using RPIO so any gpio pin can be PWM.

[ShadowLight8]

@TomasRa1 I've merged #28, but it required an FPP change that has been merged, but only to master/fpp. I've guessing the next release will have it. Until then, the hardware pwm pin change won't work.

I'll start looking into using RPIO next!

[chrkov]

I have been looking for a nice DAC that has RCA outputs. I found this (https://www.amazon.com/Decoder-Amplifier-PCM5102-PCM5102A-Headphone/dp/B0C7KQPR7S/ref=sr_1_50?crid=KTYBTOFN5CGZ&keywords=PCM5102&qid=1704083256&s=industrial&sprefix=pcm5102%2Cindustrial%2C104&sr=1-50)
and just wondering if you think this would work also? It seems to have the same connections.

[TomasRa1]

Yes, it is the same chip PCM5102A, it must also works.
I hope that connection could be:

BCK = BCK
DATA = DIN
LRCK = LCK
GND = GND
VCC = VIN

FLT=N = SCK jumper soldered (ICpin12=GND)
FMT=I2S

Please, test it and inform us regarding result if my ideas above are correct. Thank you.

[TomasRa1]

@TomasRa1 I've merged #28, but it required an FPP change that has been merged, but only to master/fpp. I've guessing the next release will have it. Until then, the hardware pwm pin change won't work.

I'll start looking into using RPIO next!

It will be nice to implement PWM via RPIO, thank you very much!
https://pythonhosted.org/RPIO/

from RPIO import PWM

# Setup PWM and DMA channel 0
PWM.setup()
PWM.init_channel(0)

# Add some pulses to the subcycle
PWM.add_channel_pulse(0, 17, 0, 50)
PWM.add_channel_pulse(0, 17, 100, 50)

# Stop PWM for specific GPIO on channel 0
PWM.clear_channel_gpio(0, 17)

# Shutdown all PWM and DMA activity
PWM.cleanup()