Frequency generation circuit

[devank.purohit]

I am using PIC18F2550. I intend to generate three sets of frequencies. One of 100 Hz, Second of (9/11/15/18 KHz) and third of 21 KHz. Is it possible with PIC18F2550? Also, 100 Hz frequency is used for modulation, meaning for the first 5 ms, I should get a (9/11/15/18) KHz frequency and for the next 5 ms, I should get a 21 KHz frequency. Please help. Thanks!

 

[apolama]

i think before doing that in PIC, try to implement in Matlab first.

 

[keith1200rs]

Use a timer to generate a 5ms interrupt and switch the PWM frequency in the interrupt routine.

Keith

 

[kripacharya]

I am using PIC18F2550. I intend to generate three sets of frequencies. One of 100 Hz, Second of (9/11/15/18 KHz) and third of 21 KHz. Is it possible with PIC18F2550? Also, 100 Hz frequency is used for modulation, meaning for the first 5 ms, I should get a (9/11/15/18) KHz frequency and for the next 5 ms, I should get a 21 KHz frequency. Please help. Thanks!

Are these square-wave or sinusoids ?

 

[devank.purohit]

@ Apolama: MATLAB?

@ Keith: Is it possible to do that? As far as I understood, one can only change the duty cycle, and not the PWM period. Please clarify.

@ Kripacharya: Square waves.

 

[keith1200rs]

In the PWM you can set period and duty cycle.

Keith

 

[kripacharya]

...
@ Kripacharya: Square waves.

in that case it should be very easy to do using the various timers.
Set the 100Hz timer for 5mS.
On completion (interrupt?) toggle the 100Hz output line - as a ref if you need it.
Also on interrupt, set a 2nd timer for 23.6uS timeout (for the 21Khz). Toggle a 2nd output on this interrupt.
etc etc

 

[devank.purohit]

@ Keith and Kripacharya: Thank you so much!