LDmicro Forum - PWM with two different frequencies.

PWM with two different frequencies. (by Magno Medeiros (Brasil))

Hello, please someone help me to create a program that sends time with PWM frequency of 20khz, time issues with PWM frequency of 40khz. time of 5 seconds for each frequency. is attached what I tried to do, but measuring with ossciloscópio see that emits only a frequency of 20 kHz.

Wed Nov 25 2015, 07:51:31, download attachment analise do funcionamento PWM (PIC) v3.ld

(no subject) (by Magno Medeiros (Brasil))

Thank you very much for your help, but unfortunately I could not do what I wanted. Intended to make a circuit to issue various sound frequencies to scare sparrows of my house, but I see on the oscilloscope that is never generated more than one frequency, although did a test by placing a piezoelectric membrane to listen to the sounds and noticed that there is a change in tone (2kHz and 4khz) experienced at various frequencies, has not worked. Still I am very grateful for your help.

Thu Nov 26 2015, 13:58:49

(no subject) (by MGP)

I do not understand fully what you want, but in this example, you can not hear frequencies of 20 and 40kHz.
Maybe a drawing of the signals will help.

Fri Nov 27 2015, 05:48:24

(no subject) (by Magno Medeiros (Brasil))

Hello friend MGP,
I know I can not hear such a high frequency, so that I said I did tests on other frequencies 1 and 2 kHz, 2 and 4khz, 4:08 khz to try to see with an oscilloscope switching frequency in PWM output, but in no tests leave the two frequencies, only one can be seen on the oscilloscope, what I saw was a change in the pulse width. I did these tests at low frequency whereas if it worked, would be also good at high frequencies. Please find attached a circuit sketch.
Thanks again for your help.

Fri Nov 27 2015, 12:26:11, download attachment For MGP.png

(no subject) (by Magno Medeiros (Brasil))

I mean: see the signal on an oscilloscope and listen on a piezo membrane, so the low frequencies. After tested change to other high frequencies that the sparrows can hear

Fri Nov 27 2015, 12:35:05

corrected KHZ (by Magno Medeiros (Brasil))

corrected KHZ

Fri Nov 27 2015, 12:41:12, download attachment For MGP.png

(no subject) (by MGP)

You're right, the only thing you do with it is to change the duty cycle_
It's also not working when you change the dutycycle to zero before changing the PWM frequency.
Maybe a bug, I'll look at it when I have time to work around it.
Perhaps Jonathan knows more about this.

Sat Nov 28 2015, 06:28:22

(no subject) (by Magno Medeiros (Brasil))

Ok MGP friend, I understanding! Anyway thank you for your dedicated time to reach these conclusions.

Sat Nov 28 2015, 13:11:39