PPMOut.h change PPM Output Pin

[Anonymous]

At the moment only PIN 9 an 10 can be used as outgoing PIN

Is there a way to modify the g_PPMOut.start(); function to hand over the out pin? For example: g_PPMOut.start(11);

I already tried to change the function but I am not sure because the "p_a" value is also used for the following line: c::Timer1::setToggle(true, p_a);

[dvdouden]

Sorry for the really late reply, I'm answering this in case someone ever has the same question and stumbles upon this :)

If I ever find the time I will add this to the library...

I recently got the same question by email, so here's my copy/paste answer:

PPM output works best with pins 9-10 since they're directly tied to
Timer 1. As timer 1 generates an interrupt, the hardware will
automatically toggle the value on either pin 9 or 10. However, it's
not that hard to make PPMOut use a different pin, you just need to
toggle the pin you want manually in the interrupt handler. For this
you need to make some changes to PPMOut.cpp:
-In PPMOut::start(), change uint8_t pin = p_a ? 9 : 10; to the pin
number you want and remove this line: rc::Timer1::setToggle(true,
p_a);
-In PPMOut::isr(), toggle your output pin on the first line of that function.

so, to summarize, you'll get something like this:

void PPMOut::start(bool p_a, bool p_invert)
{
// stop timer 1
rc::Timer1::stop();

    // Fill channelTimings buffer with data from channels buffer
    update();

    // Fill timings buffer with data from channelTimings buffer     (set up a

complete PPM frame)
updateTimings();

    uint8_t pin = <SOME PIN HERE>; // fill this in yourself
    m_timingPos = p_invert ? 0 : 1;

    pinMode(pin, OUTPUT);

    // First disable the output compare match A interrupt
    rc::Timer1::setCompareMatch(false, true);

    // set compare value
    OCR1A = TCNT1 + m_timings[p_invert ? m_timingCount - 1 : 0];

    // enable timer output compare match A interrupts
    rc::Timer1::setCompareMatch(true, true,     PPMOut::handleInterrupt);

    // start the timer
    rc::Timer1::start();

}

and

void PPMOut::isr()
{
// fill this in yourself

    // set the compare register with the next value
    OCR1A += m_timings[m_timingPos];

    // update position
    ++m_timingPos;
    if (m_timingPos >= m_timingCount)
    {
            m_timingPos = 0;

            // we're at the end of frame here, so there's plenty of time to update
            updateTimings();
    }

}

It is possible to toggle an output pin by writing to its input register

uint8_t mask = digitalPinToBitMask();
uint8_t port = digitalPinToPort();
volatile uint8_t out = portInputRegister(port);
out |= mask;

You can simply store the mask and out variable somewhere else (as
member variable of PPMOut for example) and just do *out |= mask in the
isr function. This will keep the amount of code (and time spent) in
the isr to a minimum and ensure the timing precision you want. I
didn't have a chance to test this code since I accidentally melted my
Arduino some time ago (short circuit). It should work though, the same
principle is used for generating a servo signal.

[dvdouden]

Added in [r84], still needs testing