How do I discern 2 or more simultaneous IR inputs? - c++

Question

I am trying to create a student response system for a Jeopardy-like game using cheap tv remote controls. They are infrared, NEC protocol. A serial monitor displays button press from students in order they respond.
I'm using a TSOP 4838 receiver connected to an Arduino Uno with a capacitor and so far just the serial monitor that comes with the Arduino IDE software. My code appears below.
All is working well as long as 2 or more students do not press buttons within a half-second of each other. If that happens, I get no output on the serial monitor. I'm hoping there is some change I can make to my sketch or to the IRremote.h or IRremoteInt.h files to discern the signals quicker so my display lists who clicked first.
IRremote.h:
*/
* IRremote v1.1
* By Chris Targett
* November 2011
*
* Based on Ken Shirriff's Version 0.11 of his IR-Remote library August, 2009
* https://github.com/shirriff/Arduino-IRremote
*/
#ifndef IRremote_h
#define IRremote_h
// The following are compile-time library options.
// If you change them, recompile the library.
// If DEBUG is defined, a lot of debugging output will be printed during decoding.
// TEST must be defined for the IRtest unittests to work. It will make some
// methods virtual, which will be slightly slower, which is why it is optional.
// #define DEBUG
// #define TEST
// Results returned from the decoder
class decode_results {
public:
int decode_type; // NEC, SONY, RC5, RC6, DISH, SHARP, SAMSUNG, JVC, UNKNOWN
unsigned long value; // Decoded value
unsigned long address; // address for panasonic codes
int bits; // Number of bits in decoded value
volatile unsigned int *rawbuf; // Raw intervals in .5 us ticks
int rawlen; // Number of records in rawbuf.
};
// Values for decode_type
#define NEC 1
#define SONY 2
#define RC5 3
#define RC6 4
#define DISH 5
#define SHARP 6
#define SAMSUNG 7
#define JVC 8
#define PANASONIC 9
#define UNKNOWN -1
// Decoded value for NEC when a repeat code is received
#define REPEAT 0xffffffff
// main class for receiving IR
class IRrecv
{
public:
IRrecv(int recvpin);
void blink13(int blinkflag);
int decode(decode_results *results);
void enableIRIn();
void resume();
private:
// These are called by decode
int getRClevel(decode_results *results, int *offset, int *used, int t1);
long decodeNEC(decode_results *results);
long decodeSony(decode_results *results);
long decodeSamsung(decode_results *results);
long decodeRC5(decode_results *results);
long decodeRC6(decode_results *results);
long decodeJVC(decode_results *results);
long decodeHash(decode_results *results);
long decodePanasonic(decode_results *results);
int compare(unsigned int oldval, unsigned int newval);
}
;
// Only used for testing; can remove virtual for shorter code
#ifdef TEST
#define VIRTUAL virtual
#else
#define VIRTUAL
#endif
class IRsend
{
public:
IRsend() {}
void sendNEC(unsigned long data, int nbits);
void sendSony(unsigned long data, int nbits);
void sendSamsung(unsigned long data, int nbits);
void sendRaw(unsigned int buf[], int len, int hz);
void sendRC5(unsigned long data, int nbits);
void sendRC6(unsigned long long data, int nbits);
void sendDISH(unsigned long data, int nbits);
void sendSharp(unsigned long data, int nbits);
void sendJVC(unsigned long data, int nbits, int repeat);
void sendPanasonic(unsigned long address, unsigned long data);
// private:
void enableIROut(int khz);
VIRTUAL void mark(int usec);
VIRTUAL void space(int usec);
}
;
// Some useful constants
#define USECPERTICK 50
#define RAWBUF 76
// Marks tend to be 100us too long, and spaces 100us too short
// when received due to sensor lag.
#define MARK_EXCESS 100
#endif
Here is the IRremoteInt.h
/*
* IRremote v1.1
* By Chris Targett
* November 2011
*
* Based on Ken Shirriff's Version 0.11 of his IR-Remote library August, 2009
* https://github.com/shirriff/Arduino-IRremote
*/
#ifndef IRremoteint_h
#define IRremoteint_h
#include <Arduino.h>
#define CLKFUDGE 5 // fudge factor for clock interrupt overhead
#define CLK 256 // max value for clock (timer 2)
#define PRESCALE 8 // timer2 clock prescale
#define SYSCLOCK 16000000 // main Arduino clock
#define CLKSPERUSEC (SYSCLOCK/PRESCALE/1000000) // timer clocks per microsecond
#define ERR 0
#define DECODED 1
#define BLINKLED 13
// defines for setting and clearing register bits
#ifndef cbi
#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
#endif
#ifndef sbi
#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
#endif
// clock timer reset value
#define INIT_TIMER_COUNT2 (CLK - USECPERTICK*CLKSPERUSEC + CLKFUDGE)
#define RESET_TIMER2 TCNT2 = INIT_TIMER_COUNT2
// pulse parameters in usec
#define NEC_HDR_MARK 9000
#define NEC_HDR_SPACE 4500
#define NEC_BIT_MARK 560
#define NEC_ONE_SPACE 1600
#define NEC_ZERO_SPACE 560
#define NEC_RPT_SPACE 2250
#define SONY_HDR_MARK 2400
#define SONY_HDR_SPACE 600
#define SONY_ONE_MARK 1200
#define SONY_ZERO_MARK 600
#define SONY_RPT_LENGTH 45000
#define RC5_T1 889
#define RC5_RPT_LENGTH 46000
#define RC6_HDR_MARK 2666
#define RC6_HDR_SPACE 889
#define RC6_T1 444
#define RC6_RPT_LENGTH 46000
#define SAMSUNG_HDR_MARK 4500
#define SAMSUNG_BITS 32
#define SAMSUNG_HDR_SPACE 4500
#define SAMSUNG_BIT_MARK 560
#define SAMSUNG_ONE_SPACE 1600
#define SAMSUNG_ZERO_SPACE 600
#define SHARP_BIT_MARK 245
#define SHARP_ONE_SPACE 1805
#define SHARP_ZERO_SPACE 795
#define SHARP_GAP 600000
#define SHARP_TOGGLE_MASK 0x3FF
#define SHARP_RPT_SPACE 3000
#define DISH_HDR_MARK 400
#define DISH_HDR_SPACE 6100
#define DISH_BIT_MARK 400
#define DISH_ONE_SPACE 1700
#define DISH_ZERO_SPACE 2800
#define DISH_RPT_SPACE 6200
#define DISH_TOP_BIT 0x8000
#define SHARP_BITS 15
#define DISH_BITS 16
#define JVC_HDR_MARK 8000
#define JVC_HDR_SPACE 4000
#define JVC_BIT_MARK 600
#define JVC_ONE_SPACE 1600
#define JVC_ZERO_SPACE 550
#define JVC_RPT_LENGTH 60000
#define PANASONIC_HDR_MARK 3502
#define PANASONIC_HDR_SPACE 1750
#define PANASONIC_BIT_MARK 502
#define PANASONIC_ONE_SPACE 1244
#define PANASONIC_ZERO_SPACE 370
#define TOLERANCE 25 // percent tolerance in measurements
#define LTOL (1.0 - TOLERANCE/100.)
#define UTOL (1.0 + TOLERANCE/100.)
#define _GAP 5000 // Minimum map between transmissions
#define GAP_TICKS (_GAP/USECPERTICK)
#define TICKS_LOW(us) (int) (((us)*LTOL/USECPERTICK))
#define TICKS_HIGH(us) (int) (((us)*UTOL/USECPERTICK + 1))
#ifndef DEBUG
#define MATCH(measured_ticks, desired_us) ((measured_ticks) >= TICKS_LOW(desired_us) && (measured_ticks) <= TICKS_HIGH(desired_us))
#define MATCH_MARK(measured_ticks, desired_us) MATCH(measured_ticks, (desired_us) + MARK_EXCESS)
#define MATCH_SPACE(measured_ticks, desired_us) MATCH((measured_ticks), (desired_us) - MARK_EXCESS)
// Debugging versions are in IRremote.cpp
#endif
// receiver states
#define STATE_IDLE 2
#define STATE_MARK 3
#define STATE_SPACE 4
#define STATE_STOP 5
// information for the interrupt handler
typedef struct {
uint8_t recvpin; // pin for IR data from detector
uint8_t rcvstate; // state machine
uint8_t blinkflag; // TRUE to enable blinking of pin 13 on IR processing
unsigned int timer; // state timer, counts 50uS ticks.
unsigned int rawbuf[RAWBUF]; // raw data
uint8_t rawlen; // counter of entries in rawbuf
}
irparams_t;
// Defined in IRremote.cpp
extern volatile irparams_t irparams;
// IR detector output is active low
#define MARK 0
#define SPACE 1
#define TOPBIT 0x80000000
#define NEC_BITS 32
#define SONY_BITS 12
#define JVC_BITS 32
#define MIN_RC5_SAMPLES 11
#define MIN_RC6_SAMPLES 1
#endif
and here's my sketch:
#include <IRremote.h>
#include <IRremoteInt.h>
int RECV_PIN = 11;
IRrecv irrecv(RECV_PIN);
decode_results results;
void setup()
{
Serial.begin(9600);
irrecv.enableIRIn(); // Start the receiver
}
void loop()
{
if (irrecv.decode(&results))
{
if (results.value == 551520375) { //1
Serial.println("Team 1");
}
if (results.value == 551504055) { //2
Serial.println("Team 2");
}
if (results.value == 551536695) { //3
Serial.println("Team 3");
}
if (results.value == 551495895) { //4
Serial.println("Team 4");
}
if (results.value == 551528535) { //5
Serial.println("Team 5");
}
if (results.value == 551512215) { //6
Serial.println("Team 6");
}
if (results.value == 551544855) { //7
Serial.println("Team 7");
}
if (results.value == 551491815) { //8
Serial.println("Team 8");
}
if (results.value == 551524455) { //9
Serial.println("Team 9");
}
if (results.value == 551487735) { //10
Serial.println("Team 10");
}
// Serial.println(results.value);
irrecv.resume(); // Receive the next value
}
}

Answer 1

In short - Not really and not reliably. The problem is that your system is effectively multi-dropped. The receiver is the seeing the sum of both transmitters. Where the modulation and encoded signal are summed up and thus corrupted.
I have IR toy magic wands, for dueling I have a the winner keep transmitting as to JAM the looser latter signal.
You could try to use TWO different modulation frequencies. One remote at 36K and the other at 60K. 38K is typical and there is significant overlap. I have seen 36 and 40 get heard or corrupt 38K. So I would got to the farthest ends of available demodulator chips; being 36K and 60K. However, I suspect you are using provided transmitters which may not be changed. So you will have to find some or build one.
Additionally using pre-built ones, you are at the mercy of its behavior. You stated 1/2 second. That is likely because they are re-transmitting retries and have start delays and pauses beyond that of the NEC frame being sent.
You could also implement RX/TX pairs that are different IR wavelength. However, most purchasable demodulator IC's are on standard wavelength. I also recommend not building a discrete RX when possible, as they integrated RX/Demodulators have Auto GAIN, stuff like that.