ESP8266 Community Forum

- Sat Jun 24, 2017 12:24 pm #67544 See images of 26MHz crystal, and testing PWM with timer, i only made 71KHz and 83KHz, because 77.5KHz is ~13uS, i used 14uS and 12uS (frequency of this time is correct).

26MHz Crystal:

Frequencymeter: http://i.imgur.com/X3kGqDd.jpg
Oscilloscope (Time div = 0.05uS): http://i.imgur.com/KN0S6Ul.jpg

71KHz with OS_TIMER_US:

In math, frequence of 14uS is 71428Hz, using timer i get ~71420Hz

Frequencymeter: http://i.imgur.com/8ITRoZb.jpg

83KHz with OS_TIMER_US:

In math, frequence of 12uS is 83333Hz, using timer i get ~83390Hz

Frequencymeter : http://i.imgur.com/IA1OmKr.jpg

- Sat Jun 24, 2017 12:25 pm #67545 12Mhz is probably to FTDI? I really don't know, but if you open ESP12, you see 26MHz

The crystal in my nodemcu says 12 Mhz
You are right, without measuring equipment I am lost but it is just for fun and learning.
I'm learning a lot abour timers and interruptions with this proyect.
Well it is easy with a Arduino Uno or Attiny85, it will be fun that ESP8266 won't make it.

Thanks again for your comments, all of them are apreciated.

Get fun.

no, crystal frequency IS NOT 80MHz.
take a look and see: 26MHz

so what is the 80MHz? --> the cpu clock

how do you get 80MHz from 26MHz ??? not really a multiple --> PLL (cheap) so you will have phase jitter

What quality does the crystal have ??? probably low +/- --> ???ppm --> so the 80MHz will be ???

Temperature stability will be ???

As I wrote, your generated frequency needs to be within a window of several 10Hz +/- around the 77500Hz
stable for at least 2 minutes for the clock to detect one correct packet (usually they take several for security).

Don't get me wrong: I am not saying it is impossible. But without taking into account the real conditions and without necessary measuring equipment I doubt you will make it by just blindly coding along ...

Have fun ....

i have one frequencymeter and show 26MHz from pin special function, and 77kHz too.. let's see how ESP work.. i will post images later

- Sat Jun 24, 2017 2:50 pm #67551 ok, so you see that the deviation @71kHz is much lower than @83 kHz, which is not what is expected.

The scope can't show anything about accuracy of frequency but would show irregularities (glitches) caused by background tasks (e.g. wifi)


@Dakota:

Well it is easy with a Arduino Uno or Attiny85, it will be fun that ESP8266 won't make it.

Why? Each µC is built for a certain purpose. Is it same fun that AT don't do wifi?
But you are correct about learning, that is allways good.
BTW: I get lots of fun at my day job ....

- Sat Jun 24, 2017 3:12 pm #67553 Well, the ESP8266 can generate and modulate a TV signal maybe a low frequency AM radio as well.
But you're right again, you can never presume anything. But you have to try.
If you have fun in your daily work, you are a lucky guy.
Regards, take care.

Pd. Can I see your code ? I can't generate any wave with OS_TIMER_US ? How do you get a sinus wave with OS_TIMER_US ?