infrared-serial-communication

Transmits data using an IR led to an IR receiver on a Raspberry Pi. This doesn't use LIRC.

Installation

Clone this repository:

$ git clone https://github.com/ritiek/infrared-serial-communication
$ cd infrared-serial-communication

and run:

$ make

If you get an error like this:

src/transmit.c:3:22: fatal error: wiringPi.h: No such file or directory
 #include <wiringPi.h>
                      ^
compilation terminated.

Then it's probably because you don't have WiringPi installed:

$ sudo apt install wiringpi

and then run make again.

---

The resultant binaries can be found in bin/; transmit-ir and receive-ir.

Usage

Let's say you have an IR led connected to GPIO 7 and pointed to an IR receiver connected to GPIO 4 on the Raspberry Pi. You'll first need to start the receiver to poll for input on GPIO 4:

$ ./bin/receive-ir 4

Now to transmit data through the IR led connected to GPIO 7, in a new terminal run:

$ ./bin/transmit-ir 7 "Hello. :D"

transmit-ir supports reading from stdin so you could also do something like this:

$ echo "Hello. :D" | ./bin/transmit-ir 7

If everything goes well, you should something like this in both the terminals:

H - 1001000
e - 1100101
l - 1101100
l - 1101100
o - 1101111
. - 101110
  - 100000
: - 111010
D - 1000100
 - 0
Hello. :D

Running tests

$ make test

I'm receiving incorrect characters!

I've found that the current setup works fine for me on my Raspberry Pi 2. However, it is possible that you are using an older Raspberry Pi with lower specs and may require more time in decoding the signal. It could also be that other processes are eating more CPU time. I think a real-time kernel would give more consistent and accurate results but I can't say for sure as I haven't tried it.

One thing that might help in such cases would be to try increasing the delay gaps in src/util/util.c#L5-L8. Such as for example, try changing them to:

const unsigned int BIT0BREAK = 50;
const unsigned int BIT1BREAK = 90;
const unsigned int CHARBREAK = 130;
const unsigned int TRANSFERBREAK = 170;

This will make the transfer slower but more reliable.

What else could be done?

There are currently no checks implemented for detecting or fixing errors. This would be nice to have, since I've noticed bits getting switched and similar bad things on the receiver end when transmitting long strings.

Although, I have no idea how we'd achieve something like this since the communication is unidirectional.

The current transfer rate averages at about 1.5 bytes/sec (when delay gaps in src/util/util.c#L5-L8 are not modified).

License

The MIT License

See LICENSE for more information.