PWM conflicts with I2C?

Question

I'm running Raspbian Jessie on my Raspberry Pi 3 and I'm doing a little house alarm project. When the alarm is activated the Pi should transmit FM signal of an alarm sound on a frequency that a few radios in the house will be tuned at. The program I use for transmiting FM is here and it uses PWM (on GPIO 4) to transmit FM.

Transmiting audio works as expected but the problem is present on my LCD 16x2 display (it's connected to I2C). Whenever I run the LCD and transmit in the same time the LCD starts displaying gibberish (first couple of times it even raised an I/O Error 5, but I can't reproduce it anymore). All other functions of the alarm such as arming, disarming or disabling the siren are working as expected while transmiting.

The reason I think PWM conflicts with I2C is because on this post an I2C clock is mentioned, it's on GPIO 3, but that still makes me believe there are more I2C connections between the pins (even though I didn't find them in this reference)

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The question:
How would I use the I2C LCD and transmit FM using the PWM method in the same time?

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Extra tehnical info:

• LCD is I2C LCD1602 from this kit
• LCD module source can be found here. It's rather high level so it's simpler for me and my week of experience with a Raspberry Pi.
• Last time the I/O Error was raised was at the BUS.write_byte function in the LCD module source (can't remember what line, the error doesn't occur anymore but is surely linked with the LCD problem)

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EDIT:

The Error 5 happened again (file at the github link above):

Traceback (most recent call last):
  File "alarm.py", line 432, in <module>
    setup()
  File "alarm.py", line 133, in setup
    LCD1602.clear()
  File "/home/pi/alarm/LCD1602.py", line 75, in clear
    send_command(0x01) # Clear Screen
  File "/home/pi/alarm/LCD1602.py", line 21, in send_command
    write_word(LCD_ADDR ,buf)
  File "/home/pi/alarm/LCD1602.py", line 15, in write_word
    BUS.write_byte(addr ,temp)
IOError: [Errno 5] Input/output error

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EDIT 2:

There are the pictures. I don't think anything is incorrectly connected. (Sorry about the pictures being blurry, I don't have a good camera)

Answer 1

PWM should not conflict with I2C.

Everything below presumes the (predominant) Broadcom pin numbering scheme, which does not correlate to the physical arrangement of the pins.

I've never used GPIO 4 for PWM; the normal PWM pins used are 12, 13, 18, and 19, making use of two separate PWM channels derived from one clock.

Have a look at the chart here. Note that the crossed out pins simply indicate those which aren't available on 26-pin models. Although it contains additional information, the parts we are concerned with here are pretty much lifted directly from section 6.2 of the BCM2835 Peripherals datasheet, so they are authoritative.

Notice that the normal PWM pins I've referred to have as either their default, or include as an ALT function, PWM0 or PWM1; this refers to the two channels just mentioned. The default purpose of one of them, pin 18, is access to the PCM clock, which is used for the timing of digital audio but may be turned to other purposes.

Pin 4, which you have said you are using, is not connected to any of the above. Instead, it uses "general purpose clock 0". However, I can't fine any reason to believe this affects the I2C clock, and looking around at documentation for libraries which can make use of general purpose clock 0 via GPIO 4 and the I2C bus, there is no indication that this should be problematic.

Put another way, it sounds like you have a eccentric issue. Whether this is due to a mistake in your code or connections, some physical defect in something, or the code written by someone else you are making use of (e.g., for the FM transmission) is impossible to say, but there is thus is no meaningful answer to your question because the problem you have is not reproducible in the general sense -- the "general sense" being that if you want to use PWM and I2C simultaneously there is not a problem and the "how to do it" is to just do it.

Answer 2

You can also create aditional i2c busses on the raspberry pi to solve i2c conflicts

https://www.instructables.com/id/Raspberry-PI-Multiple-I2c-Devices/