Precision generator

[RickRac]

I am keen about generating a square wave with a floating point frequency say 1 or 2 decimal points from the range of 1-20000 Hz.
Is there an easy way to do this say with a S3? 7.83 Hz for example.
Thanks

[Sprite]

The -S3 can run its PWM stuff (LEDC etc) on 80MHz. It has an 18bit divider and 14-bit counter after that, for a minimum frequency of 0.1Hz. At 200000Hz, the divider would be something like 4000, meaning if you change your divider by 1, the frequency would shift by 5Hz. However, if you're okay with some jitter in the output frequency, the divider has a fractional part, meaning you can change the divider by 1/256th, leading to a frequency shift of 0.2Hz. The LEDC does this by e.g. using a divider of 4000 for 255 cycles and then a divider of 4001 for one cycle (averaging to exactly the frequency you set), so that's the jitter you will get.

[RickRac]

Thanks for the prompt reply. A little jitter etc is all ok.
Can you offer any sample code to get started please?

[Sprite]

I think you should be able to use the LEDC examples as a starting point. Just set the duty cycle to 50%.

[RickRac]

Well the issue is freq must be an integer so no dice on 7.83. I need a version that allows floats or divide the master clock by 10.

ledcAttachChannel(7, freq, resolution, 3); //freq is an integer.

Thanks for the reply though

[Sprite]

Ah, you're right there. esp-idf also doesn't support fractional rates, I'm afraid... hm, you could use the HAL to poke into the registers directly, or file an issue on esp-idf or the esp32-arduino repos to allow for float frequencies, I guess.

[samlevy0515]

Sure, the ESP32-S3 can handle that. You'll want to use the LEDC (PWM) peripheral and set it to a high-resolution mode (like 20-bit) to get the fine decimal control you need for frequencies like 7.83 Hz.

[RickRac]

While 20 bit PW resolution is super nice, the issue remains that the freq must be an integer so no dice on 7.83

[ESP32_kid]

PWM functions need integer? Ok, so don't use PWM

1/7.83 = 0.1277139208173 sec

We can delay() to 1msec
The closest you'll get to 7.83Hz is 127 or 128msec period. 128 is the better number.
127ms period is off by -5.69ms, 128ms period is off by +2.24ms

It was never stated what % PWM @ 7.83Hz, so I assume here 50%

(esp32-c3-zero, flash the led at 7.83Hz))
neopixelWrite(RGB_BUILTIN,0,0,RGB_BRIGHTNESS); // Blue
delay(64);
neopixelWrite(RGB_BUILTIN,0,0,0); // Off / black
delay(64);

You want to change % PWM, just change on off times, as long as they add up to 127 or 128.
eg; fast pulse 1ms on, 127ms off.

It's not accurate, yet should be fairly precise, not sure how much drift there is in esp32 clock.
If it's for PPL or the like, probably won't work if 7.83 is needed within nsec accuracy.

[ESP32_kid]

And then look into time.sleep_us()
With usec sleep you can get to 7.83Hz.