Software Gate on a PWM port

Question

I'm using a PWM port and outputting a freq. Is it possible to pulse the PWM port using software to simulate a pulse gate. For example, I'd like to output a freq of 111hz, but would like to gate that freq at .5-7hz. Is this possible to do all in software without external hardware. I'm using a Teensy board which is similar to an Arduino, but has 3 independent PWM ports. Any ideas on whether this possible?

Answer 1

If you can configure the PWM to run at 111 Hz (I don't know how this is done on the Teensy), then “gating” it is as simple as turning the PWM on and off at the desired frequency:

uint32_t half_period;  // half the gating period in microseconds

void set_gate_frequency(float freq_in_hz)
{
    half_period = (1e6 / 2) / freq_in_hz;
}

void loop()
{
    static uint32_t last_toggle = 0;
    static bool pwm_is_on = false;
    if (micros() - last_toggle >= half_period) {
        if (pwm_is_on) {
            digitalWrite(PWM_PIN, LOW);
            pwm_is_on = false;
        } else {
            analogWrite(PWM_PIN, 128);  // PWM with 50% duty cycle
            pwm_is_on = true;
        }
        last_toggle += half_period;
    }
}