Trying to build an IR project

[financecatalyst]

Hi, I am trying to build an IR based transmitter and receiver. I have few questions I would like to ask:
1) Can it be done using any PIC? I have a good stock of 12f635
2) Is data transmitted by simply flashing led at 38-40kHz and controlling the time between each burst?
3) Is 0 & 1 are the only type we can send - like for eg 38kHz for 12mS=0 & 38kHz for 30mS=1 or more data can be incorporated

By knowing this I can atleast know how to proceed about it
Thanks

[dhouston]

1. Any PIC that can generate 38-40kHz should work.

2. You can control the duration of both the bursts and the idle time between bursts.

3. There are several methods used. You should Google for NEC, Sony, & Philips IR protocols. This will give you a good introduction to the most common protocols. If you want to get a bit more sophisticated, you can have multiple durations for both bursts and idle spaces. With 5 possibilities for each you can encode an enormous amount of data. For example, if you let ABCDE represent 5 burst times and abcde represent 5 idle times, you have a 10 letter alphabet to play with. However, the more complex the message, the more horsepower you need at the receiver.

EDIT: Here's a website with many of the most used protocols.

• http://www.sbprojects.com/knowledge/ir/ir.htm

[Byte_Butcher]

I found this article to be helpful:

http://www.picbasic.co.uk/support/Article.pdf



steve

[mackrackit]

Go here for good info.
http://www.rentron.com/remote.htm

[Macgman2000]

I have used a couple of methods for the transmitter, all work equally well.

1). Bit bang. Togggle a pin for a duration of 1ms or whatever cadence your receive module allows for logic "1" output. Most RX module output is inverted due to a pullup resistor on the data out line. Look at the data sheet pulse width and duration diagrams. So in your code you shift a bit and test for 1 or 0 then either pause for a zero or toggle at 38Khz for a duration of 1ms (or whatever your receive module wants to see) and do it until all 8 bits have been sent out.

Advantage: you use only 1 TX pin.
Disadvantage: you are stuck in the main loop while transmitting.

2). Hardware PWM. Configure either a 16F88, 16F877A..etc with hardware PWM to output a 38Khz pulse train. Use a 2nd I/O to output your data using serout and put your IR LED between the PWM out port and data out port. The LED will flash at 38Khz encoding your data being transmitted.

Advantage: no bit banging, you can use the built in serout to transmit serially.
Disadvantage: 2 pins

Nick

[financecatalyst]

I have used a couple of methods for the transmitter, all work equally well.

1). Bit bang. Togggle a pin for a duration of 1ms or whatever cadence your receive module allows for logic "1" output. Most RX module output is inverted due to a pullup resistor on the data out line. Look at the data sheet pulse width and duration diagrams. So in your code you shift a bit and test for 1 or 0 then either pause for a zero or toggle at 38Khz for a duration of 1ms (or whatever your receive module wants to see) and do it until all 8 bits have been sent out.

Advantage: you use only 1 TX pin.
Disadvantage: you are stuck in the main loop while transmitting.

One thing to begin with, I never know which PIC has HPWM, is it normally written in the datasheet?

I have 12F635 - is it capable to follow the above method? Is it possible you can write few lines of the code mainly to get 38kHz, I can try to manage the rest of the code. Thanks a lot

[Byte_Butcher]

Hi, Very useful document. I may be wrong but I want to confirm if it is a mistake in the document or my understanding. In listing 9 of the document, it says :

 If IR_Dec<>0 then goto again

Should it not be 1 instead of zero as in the same document towards the top it says television Device id is 1?

Yes, the Sony TV device code is 1, so that bit of code is probably wrong.

1) By the way have you got any resourse like this which can explain the transmitting part as well?

I don't have any URL's handy for transmitting but I ran across lots of that info during my brief research on receiving and decoding Sony protocol. I'm sure Google is your friend though.

2) Does it means that all Sony TVs can be controlled with same remote controll?

No. There's at least 3 different Sony protocols that I found in my brief search. Sony12, Sony15, and Sony20.
They are similar, but the number of transmitted bits varies. (12, 15, 20). The extra bits allows addressing more devices and commands.
For my purpose the simplest one, sony12 was adequate, so that's what I used.

FWIW, here's a site with a lot of good Sony IR info:
http://www.hifi-remote.com/sony/


If you are going to play with IR remotes, I'd like to recommend one of Tommy Tylers "USB IR Widgets". (Infrared signal recorder)
It plugs into a USB port and receives signals from your remote. The software that you download for it gives a great visual representation of the signal, gives duration times for the bits and spaces, operating frequency of the remote, what button was pressed, and what protocol it speaks (if the software recognizes it.) and more. For about $30 it's a handy (and fun) learning tool. If you are building your own PIC based IR transmitter,it should be a great diagnostic tool.
You can read out about the USB IR widget, and download it's software and operating instructions here. (About 1/2 way down the page):
http://www.hifi-remote.com/forums/viewtopic.php?t=9405

I have NO affiliation with Tommy or his store, but I bought a widget and like it, and it shipped fast after I ordered it. No complaints here.


Good luck!


steve

[financecatalyst]

I found this article to be helpful:

http://www.picbasic.co.uk/support/Article.pdf



steve

Hi, Very useful document. I may be wrong but I want to confirm if it is a mistake in the document or my understanding. In listing 9 of the document, it says :

 If IR_Dec<>0 then goto again

Should it not be 1 instead of zero as in the same document towards the top it says television Device id is 1?

1) By the way have you got any resourse like this which can explain the transmitting part as well?
2) Does it means that all Sony TVs can be controlled with same remote controll?