DIY PIXHAWK APM等飞控用的PPM转接板

需要的硬件

一块arduino pro mini（推荐这个，比较小，当然如果你没有USB转转口的烧写工具买个ardunio nano板也是不错的，直接用USB线连接电脑就可以，用nano板要注意。它的usb口是大一点的mini usb口，而不是我们手机那种micro usb）

一个USB的串口刷写模块，用于更新arduino pro mini，用nano板的请无视

直接上图和代码

DIY PIXHAWK APM等飞控用的PPM转接板

代码直接下载

在arduino的ide里面代码：

先建立一个名为 buzz_8pwm_to_ppm328的目录，然后在目录下建立两个文本文件：

buzz_8pwm_to_ppm328.ino

PPM_Encoder.h

用arduino的IDE打开buzz_8pwm_to_ppm328.ino 烧写进板子就可以了

两个文件的内容如下

buzz_8pwm_to_ppm328.ino

#include "Arduino.h"

#include "ppm_encoder.h"

#include <util/delay.h>

#include <avr/io.h>

#define    ERROR_THRESHOLD        2                                    // Number of servo input errors before alerting

#define ERROR_DETECTION_WINDOW    3000 * LOOP_TIMER_10MS            // Detection window for error detection (default to 30s)

#define    ERROR_CONDITION_DELAY    500 * LOOP_TIMER_10MS            // Servo error condition LED delay (LED blinking duration)

#define PASSTHROUGH_MODE_ENABLED    // Comment this line to remove CH8 radio passthrough mode support (hardware failsafe for Arduplane)

#define PASSTHROUGH_CHANNEL        8 * 2    // Channel for passthrough mode selection

#define PASSTHROUGH_CHANNEL_OFF_US        ONE_US * 1600 - PPM_PRE_PULSE    // Passthrough off threshold

#define PASSTHROUGH_CHANNEL_ON_US        ONE_US * 1800 - PPM_PRE_PULSE    // Passthrough on threshold

#define THROTTLE_CHANNEL        3 * 2    // Throttle Channel

#define THROTTLE_CHANNEL_LED_TOGGLE_US        ONE_US * 1200 - PPM_PRE_PULSE    // Throttle Channel Led toggle threshold

#define LED_LOW_BLINKING_RATE    125 * LOOP_TIMER_10MS // Led blink rate for low throttle position (half period)

// Timers

#define TIMER0_10MS        156            // Timer0 ticks for 10 ms duration

#define TIMER1_10MS        20000        // Timer1 ticks for 10 ms duration

#define TIMER2_100MS        1562    // Timer2 ticks for 100 ms duration

#define LOOP_TIMER_10MS    10            // Loop timer ticks for 10 ms duration

// LED Code

#define    SPACE_SHORT_DURATION    40 * LOOP_TIMER_10MS    // Space after short symbol

#define    SPACE_LONG_DURATION    75 * LOOP_TIMER_10MS        // Space after long symbol

#define    SYMBOL_SHORT_DURATION    20 * LOOP_TIMER_10MS    // Short symbol duration

#define    SYMBOL_LONG_DURATION    100 * LOOP_TIMER_10MS    // Long symbol duration

#define    INTER_CODE_DURATION    150 * LOOP_TIMER_10MS        // Inter code duration

#define INTER_CODE        0        // Symbols value for coding

#define SHORT_SYMBOL    1

#define LONG_SYMBOL        2

#define SHORT_SPACE        3

#define LONG_SPACE        4

#define LOOP            5

// ------------------------------------------------------------------------------------------------------------------------------------------------------------

// PPM ENCODER INIT AND AUXILIARY TASKS

// ------------------------------------------------------------------------------------------------------------------------------------------------------------

    // ------------------------------------------------------------------------------------------------------------------------------------------------------------

    // LOCAL VARIABLES

    // ------------------------------------------------------------------------------------------------------------------------------------------------------------

    bool localinit = true; // We are inside init sequence

    bool mux_passthrough = false; // Mux passthrough mode status Flag : passthrough is off

    uint16_t led_acceleration; // Led acceleration based on throttle stick position

    bool servo_error_condition = false;    //    Servo signal error condition

    static uint16_t servo_error_detection_timer=;        // Servo error detection timer

    static uint16_t servo_error_condition_timer=;         // Servo error condition timer

    static uint16_t blink_led_timer = ;         // Blink led timer

    #ifdef PASSTHROUGH_MODE_ENABLED

    static uint8_t mux_timer = ;                // Mux timer

    static uint8_t mux_counter = ;                // Mux counter

    static int8_t mux_check = ;

    static uint16_t mux_ppm = ;

    #endif

    static uint16_t led_code_timer = ;    // Blink Code Timer

    static uint8_t led_code_symbol = ;    // Blink Code current symbol

    // ------------------------------------------------------------------------------------------------------------------------------------------------------------

    // LOCAL FUNCTIONS

    // ------------------------------------------------------------------------------------------------------------------------------------------------------------

    // ------------------------------------------------------------------------------

    // Led blinking (non blocking) function

    // ------------------------------------------------------------------------------

    uint8_t blink_led ( uint16_t half_period )    // ( half_period max = 65 s )

    {

        blink_led_timer++;

        if ( blink_led_timer < half_period ) // If half period has not been reached

        {

            return ; // Exit timer function and return 0

        }

        else    // half period reached - LED Toggle

        {

            PPM_PORT ^= (  << PB0 );    // Toggle status LED

            blink_led_timer = ;    // Blink led timer reset

            return ;    // half period reached - Exit timer function and return 1

        }

    }

    // ------------------------------------------------------------------------------

    // Led code (non blocking) function

    // ------------------------------------------------------------------------------

    void blink_code_led ( uint8_t code )

    {

        const uint8_t coding[][] = {

        // PPM_PASSTROUGH_MODE

        { INTER_CODE, LONG_SYMBOL, LONG_SPACE, SHORT_SYMBOL, SHORT_SPACE, SHORT_SYMBOL, LOOP }, 

        // JETI_MODE

        { INTER_CODE, LONG_SYMBOL, LONG_SPACE, SHORT_SYMBOL, SHORT_SPACE, SHORT_SYMBOL, SHORT_SPACE, SHORT_SYMBOL,LOOP }

        };

        led_code_timer++;        

            switch ( coding [ code -  ] [ led_code_symbol ] )

            {

                case INTER_CODE:

                if ( led_code_timer < ( INTER_CODE_DURATION ) ) return;

                else PPM_PORT |= (  << PB0 );        // Enable status LED

                break;

                case LONG_SYMBOL:    // Long symbol

                if ( led_code_timer < ( SYMBOL_LONG_DURATION ) ) return;

                else PPM_PORT &= ~(  << PB0 );    // Disable status LED

                break;

                case SHORT_SYMBOL:    // Short symbol

                if ( led_code_timer < ( SYMBOL_SHORT_DURATION ) ) return;

                else PPM_PORT &= ~(  << PB0 );    // Disable status LED

                break;

                case SHORT_SPACE:    // Short space

                if ( led_code_timer < ( SPACE_SHORT_DURATION ) ) return;

                else PPM_PORT |= (  << PB0 );        // Enable status LED

                break;

                case LONG_SPACE:    // Long space

                if ( led_code_timer < ( SPACE_LONG_DURATION ) ) return;

                else PPM_PORT |= (  << PB0 );        // Enable status LED

                break;

                case LOOP:    // Loop to code start

                led_code_symbol = ;

                return;

                break;

            }

        led_code_timer = ;    // Code led timer reset

        led_code_symbol++;    // Next symbol

        return; // LED code function return

    }

    // ------------------------------------------------------------------------------

    // ppm reading helper - interrupt safe and non blocking function

    // ------------------------------------------------------------------------------

    uint16_t ppm_read( uint8_t channel )

    {

        uint16_t ppm_tmp = ppm[ channel ];

        while( ppm_tmp != ppm[ channel ] ) ppm_tmp = ppm[ channel ];

        return ppm_tmp;

    }

    // ------------------------------------------------------------------------------------------------------------------------------------------------------------

    // INITIALISATION CODE

    // ------------------------------------------------------------------------------------------------------------------------------------------------------------

void setup() {

    // ------------------------------------------------------------------------------

    // Reset Source checkings

    // ------------------------------------------------------------------------------

    if (MCUSR & )    // Power-on Reset

    {

       MCUSR=; // Clear MCU Status register

       // custom code here

    }

    else if (MCUSR & )    // External Reset

    {

       MCUSR=; // Clear MCU Status register

       // custom code here

    }

    else if (MCUSR & )    // Brown-Out Reset

    {

       MCUSR=; // Clear MCU Status register

       brownout_reset=true;

    }

    else    // Watchdog Reset

    {

       MCUSR=; // Clear MCU Status register

       // custom code here

    }

    // ------------------------------------------------------------------------------

    // Servo input and PPM generator init

    // ------------------------------------------------------------------------------

    ppm_encoder_init();

    // ------------------------------------------------------------------------------

    // Outputs init

    // ------------------------------------------------------------------------------

    PPM_DDR |= (  << PB0 );    // Set LED pin (PB0) to output

    PPM_DDR |= (  << PB1 );    // Set MUX pin (PB1) to output

    PPM_DDR |= (  << PPM_OUTPUT_PIN );    // Set PPM pin (PPM_OUTPUT_PIN, OC1B) to output

    // ------------------------------------------------------------------------------

    // Timer0 init (normal mode) used for LED control and custom code

    // ------------------------------------------------------------------------------

    TCCR0A = 0x00;    // Clock source: System Clock

    TCCR0B = 0x05;    // Set 1024x prescaler - Clock value: 15.625 kHz - 16 ms max time

    TCNT0 = 0x00;

    OCR0A = 0x00;        // OC0x outputs: Disconnected

    OCR0B = 0x00;

    TIMSK0 = 0x00;        // Timer 1 interrupt disable

    // ------------------------------------------------------------------------------

    // Enable global interrupt

    // ------------------------------------------------------------------------------

    sei();            // Enable Global interrupt flag

    // ------------------------------------------------------------------------------

    // Disable radio passthrough (mux chip A/B control)

    // ------------------------------------------------------------------------------

    PPM_PORT |= (  << PB1 );    // Set PIN B1 to disable Radio passthrough (mux)

}

void loop() {

    // ------------------------------------------------------------------------------------------------------------------------------------------------------------

    // AUXILIARY TASKS

    // ------------------------------------------------------------------------------------------------------------------------------------------------------------

    PWM_LOOP: // SERVO_PWM_MODE

    while(  )

    {

        _delay_us (); // Slow down while loop

    }    // PWM Loop end

} // main lopo function end

PPM_Encoder.h

// -------------------------------------------------------------

#ifndef _PPM_ENCODER_H_

#define _PPM_ENCODER_H_

#include <avr/io.h>

// -------------------------------------------------------------

#include <avr/interrupt.h>

#include <avr/wdt.h>

#include <util/delay.h>

// -------------------------------------------------------------

// SERVO INPUT FILTERS

// -------------------------------------------------------------

// Using both filters is not recommended and may reduce servo input resolution

// #define _AVERAGE_FILTER_         // Average filter to smooth servo input capture jitter

// #define _JITTER_FILTER_             // Cut filter to remove 0,5us servo input capture jitter

// -------------------------------------------------------------

#ifndef F_CPU

#define F_CPU               16000000UL

#endif

#ifndef true

#define true                1

#endif

#ifndef false

#define false               0

#endif

//#ifndef bool

//#define bool                boolean

//#endif

// 328 does not define PBX but defines an equivalent as PORTBX, comment these lines out if you already have a PB2 defined.

#define PB2 PORTB2

#define PB1 PORTB1

#define PB0 PORTB0 

// -------------------------------------------------------------

// SERVO INPUT MODE - !EXPERIMENTAL!

// -------------------------------------------------------------

#define SERVO_PWM_MODE        1    // Normal 8 channel servo (pwm) input

// Servo input mode (jumper (default), pwm, ppm, jeti or spektrum)

volatile uint8_t servo_input_mode = SERVO_PWM_MODE;

// -------------------------------------------------------------

// Number of Timer1 ticks in one microsecond

#define ONE_US                F_CPU / 8 / 1000 / 1000

// 400us PPM pre pulse

#define PPM_PRE_PULSE         ONE_US * 400

// -------------------------------------------------------------

// SERVO LIMIT VALUES

// -------------------------------------------------------------

// Servo minimum position

#define PPM_SERVO_MIN         ONE_US * 900 - PPM_PRE_PULSE

// Servo center position

#define PPM_SERVO_CENTER      ONE_US * 1500 - PPM_PRE_PULSE

// Servo maximum position

#define PPM_SERVO_MAX         ONE_US * 2100 - PPM_PRE_PULSE

// Throttle default at power on

#define PPM_THROTTLE_DEFAULT  ONE_US * 1100 - PPM_PRE_PULSE

// Throttle during failsafe

#define PPM_THROTTLE_FAILSAFE ONE_US * 900 - PPM_PRE_PULSE

// CH5 power on values (mode selection channel)

//#define PPM_CH5_MODE_4        ONE_US * 1555 - PPM_PRE_PULSE

// -------------------------------------------------------------

// Number of servo input channels

#define SERVO_CHANNELS        8

// PPM period 18.5ms - 26.5ms (54hz - 37Hz)

#define PPM_PERIOD            ONE_US * ( 22500 - ( 8 * 1500 ) )

// Size of ppm[..] data array ( servo channels * 2 + 2)

#define PPM_ARRAY_MAX         18

// Data array for storing ppm (8 channels) pulse widths.

volatile uint16_t ppm[ PPM_ARRAY_MAX ] =

{

    PPM_PRE_PULSE,

    PPM_SERVO_CENTER,         // Channel 1

    PPM_PRE_PULSE,

    PPM_SERVO_CENTER,         // Channel 2

    PPM_PRE_PULSE,

    PPM_THROTTLE_DEFAULT,     // Channel 3 (throttle)

    PPM_PRE_PULSE,

    PPM_SERVO_CENTER,         // Channel 4

    PPM_PRE_PULSE,

    PPM_SERVO_CENTER,           // Channel 5

    PPM_PRE_PULSE,

    PPM_SERVO_CENTER,         // Channel 6

    PPM_PRE_PULSE,

    PPM_SERVO_CENTER,         // Channel 7

    PPM_PRE_PULSE,

    PPM_SERVO_CENTER,         // Channel 8

    PPM_PRE_PULSE,

    PPM_PERIOD

};

// -------------------------------------------------------------

// SERVO FAILSAFE VALUES

// -------------------------------------------------------------

const uint16_t failsafe_ppm[ PPM_ARRAY_MAX ] =

{

    PPM_PRE_PULSE,

    PPM_SERVO_CENTER,         // Channel 1

    PPM_PRE_PULSE,

    PPM_SERVO_CENTER,         // Channel 2

    PPM_PRE_PULSE,

    PPM_THROTTLE_FAILSAFE,    // Channel 3 (throttle)

    PPM_PRE_PULSE,

    PPM_SERVO_CENTER,         // Channel 4

    PPM_PRE_PULSE,

    PPM_SERVO_MAX,           // Channel 5

    PPM_PRE_PULSE,

    PPM_SERVO_MAX,         // Channel 6

    PPM_PRE_PULSE,

    PPM_SERVO_CENTER,         // Channel 7

    PPM_PRE_PULSE,

    PPM_SERVO_CENTER,         // Channel 8

    PPM_PRE_PULSE,

    PPM_PERIOD

};

// -------------------------------------------------------------

// AVR parameters for ArduPilot MEGA v1.4 PPM Encoder (ATmega328P)

#if defined (__AVR_ATmega328P__) || defined (__AVR_ATmega328__)

#define SERVO_DDR             DDRD

#define SERVO_PORT            PORTD

#define SERVO_INPUT           PIND

// PCIE2 PC Interrupt enable 2 is for Arduino Pins (D0-D7), also called PORTD.

#define SERVO_INT_VECTOR      PCINT2_vect

#define SERVO_INT_MASK        PCMSK2

#define SERVO_INT_CLEAR_FLAG  PCIF2

#define SERVO_INT_ENABLE      PCIE2

#define SERVO_TIMER_CNT       TCNT1

#define PPM_DDR               DDRB

#define PPM_PORT              PORTB

#define PPM_OUTPUT_PIN        PB2

#define PPM_INT_VECTOR        TIMER1_COMPB_vect

#define PPM_COMPARE           OCR1B

#define PPM_COMPARE_FLAG      COM1B0

#define PPM_COMPARE_ENABLE    OCIE1B

#else

#error NO SUPPORTED DEVICE FOUND! ( ATmega328/p)

#endif

// Used to indicate invalid SERVO input signals

//volatile uint8_t servo_input_errors = 0;

// Used to indicate missing SERVO input signals

volatile bool servo_input_missing = true;

// Used to indicate if PPM generator is active

volatile bool ppm_generator_active = false;

// Used to indicate a brownout restart

volatile bool brownout_reset = false;

// ------------------------------------------------------------------------------

// PPM GENERATOR START - TOGGLE ON COMPARE INTERRUPT ENABLE

// ------------------------------------------------------------------------------

// this starts OUTGOING PPM stream on PPM_PORT (PORTB, Arduino D8-D13)  at PPM_OUTPUT_PIN (PB2, arduino pin D10)

void ppm_start( void )

{

        // Prevent reenabling an already active PPM generator

        if( ppm_generator_active ) return;

        // Store interrupt status and register flags

        uint8_t SREG_tmp = SREG;

        // Stop interrupts

        cli();

        // Make sure initial output state is low

        PPM_PORT &= ~( << PPM_OUTPUT_PIN);

        // Wait for output pin to settle

        //_delay_us( 1 );

        // Set initial compare toggle to maximum (32ms) to give other parts of the system time to start

        SERVO_TIMER_CNT = ;

        PPM_COMPARE = 0xFFFF;

        // Set toggle on compare output

        TCCR1A = ( << PPM_COMPARE_FLAG);

        // Set TIMER1 8x prescaler

        TCCR1B = (  << CS11 );

        // Enable output compare interrupt

        TIMSK1 |= ( << PPM_COMPARE_ENABLE);

        // Indicate that PPM generator is active

        ppm_generator_active = true;

        // Restore interrupt status and register flags

        SREG = SREG_tmp;

}

// ------------------------------------------------------------------------------

// PPM GENERATOR STOP - TOGGLE ON COMPARE INTERRUPT DISABLE

// ------------------------------------------------------------------------------

void ppm_stop( void )

{

        // Store interrupt status and register flags

        uint8_t SREG_tmp = SREG;

        // Stop interrupts

        cli();

        // Disable output compare interrupt

        TIMSK1 &= ~( << PPM_COMPARE_ENABLE);

        // Reset TIMER1 registers

        TCCR1A = ;

        TCCR1B = ;

        // Indicate that PPM generator is not active

        ppm_generator_active = false;

        // Restore interrupt status and register flags

        SREG = SREG_tmp;

}

// ------------------------------------------------------------------------------

// Watchdog Interrupt (interrupt only mode, no reset)

// ------------------------------------------------------------------------------

ISR( WDT_vect ) // If watchdog is triggered then enable missing signal flag and copy power on or failsafe positions

{

    // Use failsafe values if PPM generator is active or if chip has been reset from a brown-out

    if ( ppm_generator_active || brownout_reset )

    {

        // Copy failsafe values to ppm[..]

        for ( uint8_t i = ; i < PPM_ARRAY_MAX; i++ )

        {

            ppm[ i ] = failsafe_ppm[ i ];

        }

    }

    // Set missing receiver signal flag

    servo_input_missing = true;

    // Reset servo input error flag

    //servo_input_errors = 0;

}

// ------------------------------------------------------------------------------

// ------------------------------------------------------------------------------

// SERVO/PPM INPUT - PIN CHANGE INTERRUPT, for any Arduino pin D0 -> D7

// ------------------------------------------------------------------------------

ISR( SERVO_INT_VECTOR )

{

    // Servo pulse start timing

    static uint16_t servo_start[ SERVO_CHANNELS ] = { , , , , , , ,  };

    // Missing throttle signal failsafe

    static uint8_t throttle_timeout = ;

    // Servo input pin storage

    static uint8_t servo_pins_old = ;

    // Used to store current servo input pins

    uint8_t servo_pins;

    // Read current servo pulse change time

    uint16_t servo_time = SERVO_TIMER_CNT;

    // ------------------------------------------------------------------------------

    // SERVO PWM MODE

    // ------------------------------------------------------------------------------

CHECK_PINS_START: // Start of servo input check

    // Store current servo input pins

    servo_pins = SERVO_INPUT;

    // Calculate servo input pin change mask

    uint8_t servo_change = servo_pins ^ servo_pins_old;

    // Set initial servo pin and channel

    uint8_t servo_pin = ;

    uint8_t servo_channel = ;

CHECK_PINS_LOOP: // Input servo pin check loop

    // Check for pin change on current servo channel

    if( servo_change & servo_pin )

    {

     // if (( servo_pin == 1  )  && (  ppm_generator_active = false) ) ppm_start();

     // if (( servo_pin == 8  )  && (  ppm_generator_active = true) ) ppm_stop();

        // High (raising edge)

        if( servo_pins & servo_pin )

        {

            servo_start[ servo_channel ] = servo_time;

        }

        else

        {

            // Get servo pulse width

            uint16_t servo_width = servo_time - servo_start[ servo_channel ] - PPM_PRE_PULSE;

            // Calculate servo channel position in ppm[..]

            uint8_t _ppm_channel = ( servo_channel <<  ) + ;

           // Check that servo pulse signal is valid before sending to ppm encoder

            if( servo_width > PPM_SERVO_MAX ) goto CHECK_PINS_ERROR;

            if( servo_width < PPM_SERVO_MIN ) goto CHECK_PINS_ERROR;

            goto CHECK_PINS_NOERROR;

            CHECK_PINS_ERROR:

                // on width input error, use defailt/failsave value, OR previous value    

               // choose the error handling type here!

                #define FAILHOLD 1

                #ifdef FAILCENTRE

                servo_width = failsafe_ppm[ _ppm_channel ]; // failsafe defaults, most channels centred, throttle lowered.

                #endif

                #ifdef FAILHOLD

                servo_width = ppm[ _ppm_channel ]; // all channels hold their previous position!

                #endif

             CHECK_PINS_NOERROR:

        //Reset throttle failsafe timeout

        if( _ppm_channel ==  ) throttle_timeout = ;

        #ifdef _AVERAGE_FILTER_

            // Average filter to smooth input jitter

            servo_width += ppm[ _ppm_channel ];

            servo_width >>= ;

        #endif

        #ifdef _JITTER_FILTER_

            // 0.5us cut filter to remove input jitter

            int16_t ppm_tmp = ppm[ _ppm_channel ] - servo_width;

            if( ppm_tmp ==  ) goto CHECK_PINS_NEXT;

            if( ppm_tmp == - ) goto CHECK_PINS_NEXT;

        #endif

            // Update ppm[..]

            ppm[ _ppm_channel ] = servo_width;

        }

    }

CHECK_PINS_NEXT:

    // Select next servo pin

    servo_pin <<= ;

    // Select next servo channel

    servo_channel++;

    // Check channel and process if needed

    if( servo_channel < SERVO_CHANNELS ) goto CHECK_PINS_LOOP;

    goto CHECK_PINS_DONE;

    // All servo input pins has now been processed

CHECK_PINS_DONE:

    // Reset Watchdog Timer

    wdt_reset(); 

    // Set servo input missing flag false to indicate that we have received servo input signals

    servo_input_missing = false;

    // Store current servo input pins for next check

    servo_pins_old = servo_pins;

    // Start PPM generator if not already running

    if( ppm_generator_active == false ) ppm_start();

    // Throttle failsafe

    if( throttle_timeout++ >=  )

    {

        // Reset throttle timeout

        throttle_timeout = ;

        // Set throttle failsafe value

        ppm[  ] = PPM_THROTTLE_FAILSAFE;

    }

    //Has servo input changed while processing pins, if so we need to re-check pins

    if( servo_pins != SERVO_INPUT ) goto CHECK_PINS_START;

    // Clear interrupt event from already processed pin changes

    PCIFR |= ( << SERVO_INT_CLEAR_FLAG);

}

// ------------------------------------------------------------------------------

// ------------------------------------------------------------------------------

// PPM OUTPUT - TIMER1 COMPARE INTERRUPT

// ------------------------------------------------------------------------------

ISR( PPM_INT_VECTOR )

{

    // Current active ppm channel

    static uint8_t ppm_channel = PPM_ARRAY_MAX - ;

    // Update timing for next compare toggle

    PPM_COMPARE += ppm[ ppm_channel ];

    // Select the next ppm channel

    if( ++ppm_channel >= PPM_ARRAY_MAX )

    {

        ppm_channel = ;

    }

}

// ------------------------------------------------------------------------------

// ------------------------------------------------------------------------------

// PPM READ - INTERRUPT SAFE PPM SERVO CHANNEL READ

// ------------------------------------------------------------------------------

/* uint16_t ppm_read_channel( uint8_t channel )

{

    // Limit channel to valid value

    uint8_t _channel = channel;

    if( _channel == 0 ) _channel = 1;

    if( _channel > SERVO_CHANNELS ) _channel = SERVO_CHANNELS;

    // Calculate ppm[..] position

    uint8_t ppm_index = ( _channel << 1 ) + 1;

    // Read ppm[..] in a non blocking interrupt safe manner

    uint16_t ppm_tmp = ppm[ ppm_index ];

    while( ppm_tmp != ppm[ ppm_index ] ) ppm_tmp = ppm[ ppm_index ];

    // Return as normal servo value

    return ppm_tmp + PPM_PRE_PULSE;

}

*/

// ------------------------------------------------------------------------------

// ------------------------------------------------------------------------------

// PPM ENCODER INIT

// ------------------------------------------------------------------------------

void ppm_encoder_init( void )

{

    // SERVO/PPM INPUT PINS

    // ------------------------------------------------------------------------------

    // Set all servo input pins to inputs

    SERVO_DDR = ;

    // Activate pullups on all input pins

    SERVO_PORT |= 0xFF;

    // SERVO/PPM INPUT - PIN CHANGE INTERRUPT

    // ------------------------------------------------------------------------------

    if( servo_input_mode == SERVO_PWM_MODE )

    {

        // Set servo input interrupt pin mask to all 8 servo input channels

        SERVO_INT_MASK = 0xFF;

    }

    // Enable servo input interrupt

    PCICR |= ( << SERVO_INT_ENABLE);

    // PPM OUTPUT PIN

    // ------------------------------------------------------------------------------

    // Set PPM pin to output

    PPM_DDR |= ( << PPM_OUTPUT_PIN);

    // ------------------------------------------------------------------------------

    // Enable watchdog interrupt mode

    // ------------------------------------------------------------------------------

    // Disable watchdog

    wdt_disable();

     // Reset watchdog timer

    wdt_reset();

     // Start timed watchdog setup sequence

    WDTCSR |= (<<WDCE) | (<<WDE );

    // Set 250 ms watchdog timeout and enable interrupt

    WDTCSR = (<<WDIE) | (<<WDP2);

}

// ------------------------------------------------------------------------------

#endif // _PPM_ENCODER_H_

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