Read Receiver
This code uses pin change interrupts and timer 1 to mesure the time between the rise and fall of 3 channels of PPM (Though often called PWM, see this Arduino Forum thread) on a typical RC car reciver. It could be extended to as many channels as you like. It uses the PinChangeInt library to notice when the signal pin goes high and low, and the Timer1 library to record the time between.
/* Copyright 2011 Lex Talionis (Lex.V.Talionis at gmail) This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This code uses pin change interrupts and timer 1 to mesure the time between the rise and fall of 3 channels of PPM (Though often called PWM, see http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1253149521/all) on a typical RC car reciver. It could be extended to as many channels as you like. It uses the PinChangeInt library to notice when the signal pin goes high and low, and the Timer1 library to record the time between. */ #include <PinChangeInt.h> // http://playground.arduino.cc/Main/PinChangeInt #include <PinChangeIntConfig.h> #include <TimerOne.h> // http://playground.arduino.cc/Code/Timer1 #define NO_PORTB_PINCHANGES //PinChangeInt setup #define NO_PORTC_PINCHANGES //only port D pinchanges (see: http://playground.arduino.cc/Learning/Pins) #define PIN_COUNT 3 //number of channels attached to the reciver #define MAX_PIN_CHANGE_PINS PIN_COUNT #define RC_TURN 3 //arduino pins attached to the reciver #define RC_FWD 2 #define RC_FIRE 4 byte pin[] = {RC_FWD, RC_TURN, RC_FIRE}; //for maximum efficency thise pins should be attached unsigned int time[] = {0,0,0}; // to the reciver's channels in the order listed here byte state=0; byte burp=0; // a counter to see how many times the int has executed byte cmd=0; // a place to put our serial data byte i=0; // global counter for tracking what pin we are on void setup() { Serial.begin(115200); Serial.print("PinChangeInt ReciverReading test"); Serial.println(); //warm up the serial port Timer1.initialize(2200); //longest pulse in PPM is usally 2.1 milliseconds, //pick a period that gives you a little headroom. Timer1.stop(); //stop the counter Timer1.restart(); //set the clock to zero for (byte i=0; i<3; i++) { pinMode(pin[i], INPUT); //set the pin to input digitalWrite(pin[i], HIGH); //use the internal pullup resistor } PCintPort::attachInterrupt(pin[i], rise,RISING); // attach a PinChange Interrupt to our first pin } void loop() { cmd=Serial.read(); //while you got some time gimme a systems report if (cmd=='p') { Serial.print("time:\t"); for (byte i=0; i<PIN_COUNT;i++) { Serial.print(i,DEC); Serial.print(":"); Serial.print(time[i],DEC); Serial.print("\t"); } Serial.print(burp, DEC); Serial.println(); /* Serial.print("\t"); Serial.print(clockCyclesToMicroseconds(Timer1.pwmPeriod), DEC); Serial.print("\t"); Serial.print(Timer1.clockSelectBits, BIN); Serial.print("\t"); Serial.println(ICR1, DEC);*/ } cmd=0; switch (state) { case RISING: //we have just seen a rising edge PCintPort::detachInterrupt(pin[i]); PCintPort::attachInterrupt(pin[i], fall, FALLING); //attach the falling end state=255; break; case FALLING: //we just saw a falling edge PCintPort::detachInterrupt(pin[i]); i++; //move to the next pin i = i % PIN_COUNT; //i ranges from 0 to PIN_COUNT PCintPort::attachInterrupt(pin[i], rise,RISING); state=255; break; /*default: //do nothing break;*/ } } void rise() //on the rising edge of the currently intresting pin { Timer1.restart(); //set our stopwatch to 0 Timer1.start(); //and start it up state=RISING; // Serial.print('r'); burp++; } void fall() //on the falling edge of the signal { state=FALLING; time[i]=readTimer1(); // read the time since timer1 was restarted // time[i]=Timer1.read(); // The function below has been ported into the // the latest TimerOne class, if you have the // new Timer1 lib you can use this line instead Timer1.stop(); // Serial.print('f'); } unsigned long readTimer1() //returns the value of the timer in microseconds { //rember! phase and freq correct mode counts //up to ICR1 then down again unsigned int tmp=TCNT1; char scale=0; switch (Timer1.clockSelectBits) { case 1:// no prescalse scale=0; break; case 2:// x8 prescale scale=3; break; case 3:// x64 scale=6; break; case 4:// x256 scale=8; break; case 5:// x1024 scale=10; break; } while (TCNT1==tmp) //if the timer has not ticked yet { //do nothing -- max delay here is ~1023 cycles } tmp = ( (TCNT1>tmp) ? (tmp) : (ICR1-TCNT1)+ICR1 );//if we are counting down add the top value //to how far we have counted down return ((tmp*1000L)/(F_CPU /1000L))<<scale; }