Idea to improve RF noise from SPI lines

[zygmund2000]

However, the main reason for the idea is the noticeable emission of signals coming from the SPI bus, good choice is to use resistors close to pins outputs, but the best solution is to change speed of rising and falling edges internally in MCU.
ESP32 also has this feature and I found in documentation how to use that:
https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/peripherals/gpio.html#_CPPv425gpio_set_drive_capability10gpio_num_t16gpio_drive_cap_t
Maybe there is someone here who can help me find it in the code, because it can reduce spurs up to 10db without loss of data.

Thanks

[PE5PVB]

The link you provided doesn't work.

[HyperDX]

Try here:
https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/peripherals/gpio.html#_CPPv425gpio_set_drive_capability10gpio_num_t16gpio_drive_cap_t

[zygmund2000]

Yes, I added to main code .ino two lines:
gpio_set_drive_capability((gpio_num_t) 18, GPIO_DRIVE_CAP_0);
gpio_set_drive_capability((gpio_num_t) 23, GPIO_DRIVE_CAP_0);

And now signal is much more smooth, no overshots, spurs are lower, and LCD still work without problems.

[PE5PVB]

Thanks. I added:
gpio_set_drive_capability((gpio_num_t) 5, GPIO_DRIVE_CAP_0);
gpio_set_drive_capability((gpio_num_t) 16, GPIO_DRIVE_CAP_0);
gpio_set_drive_capability((gpio_num_t) 17, GPIO_DRIVE_CAP_0);
gpio_set_drive_capability((gpio_num_t) 18, GPIO_DRIVE_CAP_0);
gpio_set_drive_capability((gpio_num_t) 19, GPIO_DRIVE_CAP_0);
gpio_set_drive_capability((gpio_num_t) 23, GPIO_DRIVE_CAP_0);

Much more quiet now.

[kkonradpl]

The I²C bus interference can be also lowered with:

gpio_set_drive_capability((gpio_num_t)21, GPIO_DRIVE_CAP_0);
gpio_set_drive_capability((gpio_num_t)22, GPIO_DRIVE_CAP_0);

With this settings the interference level is decreased or is even below noise level. See the example, this is PE5PVB board without antenna connected and without display, running my sketch: https://www.youtube.com/watch?v=GVjCEUiXoLE
Antenna input alignment is used for GPIO_DRIVE_CAP manipulation, i.e.:
0 - GPIO_DRIVE_CAP_0
1 - GPIO_DRIVE_CAP_1
2 - GPIO_DRIVE_CAP_2
3 - GPIO_DRIVE_CAP_3
4 - GPIO_DRIVE_CAP_DEFAULT

[kkonradpl]

Just an update: this test above was at 400 kHz bus speed.

On regular 100 kHz there is audible interference every 100 kHz without antenna connected, which sounds like a weak empty carrier. With the GPIO_DRIVE_CAP_0 set, the interference on the FM band is gone.

[PE5PVB]

I added the lines, and it works.