Frsky anyone? :)

[Anonymous]

Hi,

im trying this lib with my FrSKY modules. Got one DHT Hack Module on my Arduino Mini (5V, 16MHz) and a CPPM receiver at my Mega.

Receiver is working (need to use pin 53 for CPPM input)

But the sender... Dont know how to setup the pulse & pause lengths... any help ? :)

Regards, Frederik

[dvdouden]

RC equipment usually isn't that picky when it comes to pulse and pause lengths. 500 microseconds for pulse and 10000 for pause should be a good starting point.

[Anonymous]

Hm, cat get it.

got some other code, but i want to use your lib

void setupPPM() {

  // configure Timer1 for PPM generation
  noInterrupts();
  TCCR1A = B00110001;   // COM1B1, COM1B0, WGM10 set to 1 (8-bit register)
  TCCR1B = B00010010;   // WGM13 & CS11 set to 1 (8-bit register)
  TCCR1C = B00000000;
  TIMSK1 = B00000010;   // All interrupts are individually masked with the Timer Interrupt Mask Register TIMSK1
  TIFR1  = B00000010;       // Int on compare B
  OCR1A = PPM_PERIOD;   // PPM frequency (double buffered Output Compare 16-bit Register)
  OCR1B = PPM_LOW;      // (double buffered Output Compare 16-bit Register), hard-wired to PPM_PIN 
  interrupts();

}

// Generate PPM sequence
ISR(TIMER1_COMPA_vect) {
  static byte Chan_idx_byt = CHANNELS;
  static word Chan_pulse_int[CHANNELS]; // pulse widths (microseconds)
  static word Sum_int = 0;

  if (Chan_idx_byt < CHANNELS) {
    word chanpulse_int = Chan_pulse_int[Chan_idx_byt++];
    // send current channel pulse
    OCR1A = chanpulse_int;
    Sum_int += chanpulse_int;
  }
  else {
    // send final sync pulse
    Chan_idx_byt = 0;
    OCR1A = PPM_PERIOD - Sum_int;
    Sum_int = 0;
    // Read input controls and update Chan_pulse_int[]
    // Execution time: [2308, 2324] microseconds < OCR1A
    for (byte chan_byt = 0; chan_byt < CHANNELS; chan_byt++) {
      word control_value_int = 0;
#ifdef TEST_MODE
      if (RunMode_int == RUNMODE_TEST)
        control_value_int = get_test_value(chan_byt);
      else
#endif
        control_value_int = read_control(chan_byt);
      Chan_pulse_int[chan_byt] =  compute_channel_pulse(chan_byt, control_value_int, true);
    }
    if (RequestPpmCopy_bool) {
      // copy the PPM sequence values into global array for the "print ppm" command
      for (byte chan_byt = 0; chan_byt < CHANNELS; chan_byt++)
        PpmCopy_int[chan_byt] = Chan_pulse_int[chan_byt] ;
      RequestPpmCopy_bool = false;
    }
  }
}

// Compute the channel pulse corresponding to given analog value
// chan_byt : 0-based, channel number - 1
// ana_value_int : read from input: [0,1023]
// enable_calibration_bool : true=apply calibration data to analog input controls, false=do not apply calibration
// Return value: PWM pulse width, microseconds
word compute_channel_pulse(byte chan_byt, word ana_value_int, boolean enable_calibration_bool) {
    word retval_int = 0;
    float value_flt = ana_value_int;

    // Map analog inputs to PPM rates
    retval_int =  map(constrain(value_flt, 0, 1023), 0, 1023, pwm_min, pwm_max);

    // Limit pulse pulse width between CHAN_PWL, CHAN_PWH
    retval_int = constrain(retval_int, pwm_min, pwm_max);

    return retval_int;
}

[dvdouden]

That code looks okay. I'd probably do things a bit differently but I don't see any big issues. If you want to use my code, check out the PPMOut class and its example.

[Anonymous]

Hm, i have tried to find the differences. but i dont find the catch...

[Anonymous]

btw, i use the following timing params for the code above:

const word PPM_PERIOD = 20000; // microseconds; send PPM sequence every 20ms for 6 channels
const word PPM_LOW = 400; // microseconds; fixed channel sync pulse width in the PPM signal

[dvdouden]

http://diydrones.com/profiles/blogs/why-frsky-cppm-signal-is-so-disappointing
try 18000 or 27000 for PPM_PERIOD, it seems to be what FRSky is using.

[Anonymous]

PPM_PERIOD = 20000 is ok for the above code. My problem is: dont know what to pulse & pause in your code. :)

Tried some combin ations but still no luck. The servo at the receiver is shacking in al directions every second

[Anonymous]

Great, SourceForge won't let me post under my own name again...

Aaah, you should've said that in the first place ;)

400 for pulse, about 4000 for pause should be enough. PPMOut has a variable frame width, I'm not sure how well FRSky will deal with that, but it shouldn't be a problem (a lot of (cheap) transmitters work this way).

If that doesn't work, try replacing updateTimings in PPMOut.cpp with the following:

void PPMOut::updateTimings()
{
    uint16_t* scratch = m_timings;
    uint16_t pause = m_pauseLength;
    // copy all pre-calculated timings
    for (uint8_t i = 0; i < m_channelCount; ++i)
    {
        // set pulse length
        *scratch = m_pulseLength;
        ++scratch;
        // set timing
        *scratch = m_channelTimings[i] - m_pulseLength;
        pause -= m_channelTimings[i];
        ++scratch;
    }
    // set final pulse length
    *scratch = m_pulseLength;
    ++scratch;
    // set pause length
    *scratch = pause - m_pulseLength;
    // update number of timings
    m_timingCount = (m_channelCount + 1) * 2;
}

and set pause length to 20000, this will make PPMOut generate a fixed width frame.

[Anonymous]

Ah! Thanks, will try it later @home!

[Anonymous]

Ok, patched PPM Code working like a charm :)

My Projekt btw: http://dt.pe/GAl2nw

[Anonymous]

Great! Glad it works, I'll put in on my patch list :)

And holy f..., is that a remote controlled lawnmower? O_O

DvdOuden (SourceForge acting up again)

[Anonymous]

It is ;)

[Anonymous]

Small Video. Much use of the Library (ppmin, expo & dualrate)

http://youtu.be/hcQXAF7YBXM

[Anonymous]

That's just awesome :)

[Anonymous]