The PwmOut interface is used to control the frequency and mark-space ratio of a digital pulse train.

Hello World!¶

#include "mbed.h"

PwmOut led(LED1);

int main() {
    while(1) {
        for(float p = 0.0f; p < 1.0f; p += 0.1f) {
            led = p;
            wait(0.1);
        }
    }
}

API¶

API summary

Details¶

The hardware has 6 PWM channels, and the PwmOut Interface can be used on mbed pins p21-p26.

The default period is 0.020s, and the default pulsewidth is 0.

The PwmOut interface can express the pulse train in many ways depening on how it is to be used. The period and pulse width can be expressed directly in units of seconds, millisecond or microseconds. The pulsewidth can also be expressed as a percentage of the the period.

Implementation details¶

LPC2368 and LPC1768¶

You can also specify the LED1-LED4 as PwmOut. Note that these are just different pinout options for the same underlying PWM hardware, so they are just alternative routing rather than extra PWM channels. So you can pin them out can't be used at the same time:

On the mbed LPC2368 and LPC1768, the PwmOut hardware is limited to share the period value between all outputs. Therefore, if you change the period of one output, you change them all. The pulsewidth can be set independently for each output.

LPC11U24¶

Pin under the same "Timer" share the same period:

Examples¶

#include "mbed.h"

PwmOut servo(p21);

int main() {
    servo.period(0.020);          // servo requires a 20ms period
    while (1) {
        for(float offset=0.0; offset<0.001; offset+=0.0001) {
            servo.pulsewidth(0.001 + offset); // servo position determined by a pulsewidth between 1-2ms
            wait(0.25);
        }
    }
}