Important changes to forums and questions
All forums and questions are now archived. To start a new conversation or read the latest updates go to forums.mbed.com.
8 years, 5 months ago.
can i use PWM to generate 2 individual square waves? (Nucleo F411)
I want to generate 2 square waves with 50% duty cycle in the range of 0 - 25kHz. The waves need to have a varying period and both running simultaneously at different frequencies.
The following example shows the period can be set
example
#include "mbed.h"
PwmOut mypwm(PWM_OUT);
DigitalOut myled(LED1);
int main() {
mypwm.period_ms(10);
mypwm.pulsewidth_ms(1);
printf("pwm set to %.2f %%\n", mypwm.read() * 100);
while(1) {
myled = !myled;
wait(1);
}
}
Can i set this to 2 different PWM outputs? The pinout of the board (link below) suggests this is possible can anybody confirm? https://developer.mbed.org/platforms/ST-Nucleo-F411RE/
I'm assuming that the PWM has its own dedicated timer, is this correct?
Also the pinout uses notation such as PWM1/1, PWM2/1, PWM1/2 and ect. any idea what this means?
1 Answer
8 years, 5 months ago.
You may want to double check this since it varies platform to platform but I think you'll be OK as long as you pick the pins carefully. On some platforms PWM outputs can each have a different duty cycle but must all use a common frequency.
From memory on the F411 all of the PWM1/n outputs use the same timer and so must have the same frequency but the PWM2/n pins will be on a different timer and so can use a different frequency. As long as you use pins that are on different timers you should be OK.
I can confirm tested 2 different frequencies and worked fine when checking on the scope.
#include "mbed.h"
PwmOut ch1(D7); //PWM1/1
PwmOut ch2(D6); //PWM2/3
DigitalOut myled(LED1);
int main() {
while(1) {
ch1.period_us(100);
ch1.write(0.5);
ch2.period_us(50);
ch2.write(0.5);
myled = !myled;
wait(1);
}
}