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Frequency generation circuit

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devank.purohit

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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!
 

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

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

Keith
 

devank.purohit said:
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!
Click to expand...

Are these square-wave or sinusoids ?
 

@ 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.
 

devank.purohit said:
...
@ Kripacharya: Square waves.
Click to expand...

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
 

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