/*

* IR Remote Control signal forwarder

*

* Objective:

*

* This program forwards IR pulses (modulated on a 38 kHz carrier wave) from a

* 3-pin IR receiver (such as a PNA4602, IRM-3638N3, or similar) with its data

* pin connected to ICP1/PB0 (Arduino pin #8) to an IR LED (connected to

* OC2A/PB3 (Arduino pin #11)). The forwarded IR pulses are also printed to the

* Serial console as a series of pulse timings (in usecs).

*

* Mode of operation:

*

* The IR receiver filters out the 38 kHz carrier wave and pulls the ICP1 pin

* low whenever there an IR pulse is detected (i.e. the 38 kHz carrier is

* present), thus triggering Timer1's Input Capture logic and the corresponding

* TIMER1_CAPT interrupt. The TIMER1_CAPT ISR first turns on/off the carrier

* wave hooked up to the IR LED (see below) so as to replicate the IR pulse

* there, and then records the length of the last IR pulse.

*

* The IR LED is fed by a 38 kHz carrier wave that is modulated by calling the

* IR_toggle() macro. The carrier wave is generated by running Timer/Counter2

* in CTC mode with the value of OCR2A register chosen such that the timer is

* automatically reset twice in each 38 kHz cycle. The COM2A1:0 bits then

* determine whether the OC2A output (to which the IR LED is connected) is

* either toggled (producing the 38 kHz carrier) - or cleared (producing no

* carrier) on each timer reset. Thus, the generation of the 38 kHz carrier

* wave itself does not consume any CPU time; only modulating it (by calling

* IR_toggle() from the TIMER1_CAPT ISR consumes CPU time.

*

* The only remaining part of the program is printing the IR pulse timings to

* the serial port. The IR timings are recorded by the TIMER1_CAPT ISR into a

* simple ring buffer. The main loop of the program then monitors this ring

* buffer, and prints the recorded timings as ASCII decimal integers (unit is

* usec) to the serial port (@ 115200 baud).

*

* Physical considerations:

*

* The point of an IR forwarder is to make an IR signal available where is

* normally would not reach. Hence, the IR receiver should be located where

* the IR signal is available, and the IR LED where the signal is not (yet)

* available. More importantly, the IR receiver must not be able to detect

* the IR pulses emitted by the IR LED, as that will mess things up.

* This means that there will probably be considerably physical distance

* between the IR receiver and the IR LED. In this case, it is recommended to

* place the Arduino as close to the IR receiver as possible, and then run a

* cable (which type?) to the IR LED. If you need to amplify the IR LED signal

* (e.g. to boost the range of the forwarded signal), then use a simple

* transistor circuit, such as https://www.sparkfun.com/products/10732 .

*

* Author: Johan Herland <johan@herland.net>

* License: GNU GPL v2 or later

*/

volatile unsigned short ring_buffer[256] = { 0 };

volatile byte rb_write; // current write position in ring buffer

byte rb_read; // current read position in ringbuffer

void setup(void)

}

/*

* Modulate the IR output carrier by switching between

* - COM2A1:0 == 0b01 (Toggle OC2A on compare match, i.e. carrier present)

* - COM2A1:0 == 0b10 (Clear OC2A on compare match, i.e. carrier absent)

* The other bits in TCCR2A must not be changed from their initialized value.

*/

#define IR_toggle() (TCCR2A ^= (_BV(COM2A1) | _BV(COM2A0)))

// Timer1 Capture Event interrupt handler. Triggered on every incoming IR pulse

// event, typically no more often than every ~100 usecs.

ISR(TIMER1_CAPT_vect)

}

// Timer1 Overflow interrupt handler. With 64 x prescaler and 16 MHz system

// clock this is triggered every ~262 msecs.

ISR(TIMER1_OVF_vect)

}

void loop(void)

}