Universal remote control

[Markdem]

Hello all, sorry if this is a bit off topic. I am tiring to make an IR to RS232 converter. Basically I want to send commands from a universal remote control (Logitech harmony 880) and then send commands to a light controller (Clipsal C-BUS). My devise will not send IR commands. The universal remote is a learning type, but what do I need to do to teach it? Do I need to first make a device that can first program the remote, and then make the receiver, or is there another way, programming the remote from my PC’s IRDA port maybe? Also, what IR decoders should I use? I have found that a TSOP1738 is common, is it going to do what I need??

Thanks, Mark

[Markdem]

I just read my question back to myself, and it made no sence . i guess the question i should be asking is how can i program my universal remote without making somthing that can send it the commands in the first place? can somthing like this be done, or am i dreaming??

Thanks, Mark

[asmallri]

A universal remote attempts to repeat the infrared pattern it has detected. There are different encoding frequencies but if you make one with a 38KHz encoding frequency then most remotes should be able to learn the sequence. You could make it easier on yourself by basing you device on a common protocol. Even better when you emulate a specific remote.

Take an exisiting remote (Sony are common) and have your device emulate it. This has the advantage that you can preprogram the auto learning remote to replicate a Sony (for example) in this case it does not really need to learn plus it gives you a wide range of options in terms of what remote to use.

There are standard IR receivers that provide an output pulse stream corresponding to the encoded signal. You need to get one of these that matches the encoding frequency you are using. For example a 36KHz IR receiver works poorly with a 38KHz encoded signal.
_________________
Regards, Andrew

http://www.brushelectronics.com/software
Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!!

[deltatech]

Try this link you may find what you are looking for there

http://www.zilog.com/application/application.asp?appid=3

[Douglas Kennedy]

To avoid re inventing the wheel use as was recommened an existing protocol and frequency. IR is very noisy mostly it's flourescent lights that make the mischief. The protocols that have been perfected by Sony and other TV manufacturers will reject this noise by either pulse width ( o and 1 are identified by the length of the pulse) encoding or space width encoding ( same as pulse only using space)or shift encoding ( 1 is long pulse short space 0 is short pulse long space) and further protect with redundancy ... sending the signal twice sending the signal followed by its inverse etc.
Here is some code that is the inverse of what you want...You wanted your PIC to train your universal remote but you are dead at the outset since you have no Tx capability. The code below is the PIC learning or at least identifying the signal from various remotes. It will not work on any remote only the ones I had laying around the house but the code might be of use to you.

[newguy]

As was suggested, take existing code (there are at least two examples in the Code Library that I know of), and use that to create an IR receiver. Short of having a decent digital oscilloscope, there is no way to determine what code, or the code format, a remote control is sending. Once you know the code and format, then you can write a program to send these codes to the learning remote.

Some notes:
- There something like 6 major code formats, and almost all A/V equipment use one of these formats. Then there are a LOT of lesser-used codes, usually employed by such well known brands as Loewe Opta, Cmwell, and Alba.
- The major codes usually follow a signaling scheme like this:

1. Lead in sequence - a long burst of IR at the carrier frequency (usually 38 - 40 kHz), followed by a shorter period of silence. May or may not be present (most Sony codes do not have a lead in sequence).
2. First data payload. Can be 8 - 32 bits long.
3. Lead out/pause. All formats employ a short pause (short IR burst followed by a relatively long pause - not as long as the lead-in, if present).
4. Repeat of data OR transmission of new data.
5. Pause. --> Usually the end of the transmission for most formats.
6. Repeat of data OR new data. Sony typically at a minimum will transmit 15 bits three times. In all cases I've examined, it's the same data.

As someone has already said, the actual 1 & 0 format varies as well. Here are the common ones:
- Short burst (constant), short pause = one state, short burst (constant), long pause = other state. I'm not actually going to say one is a 0 and the other is a 1 because I don't remember which is which (and this prevents someone from correcting me )
- Short burst, short pause (constant), and long burst, short pause (constant).

There are many variations on this theme.

I developed a product that features an IR passthru feature - the operator points an ordinary IR remote at a touch screen, and is able to control the A/V equipment which is locked away in a vault. The commands are received, decoded, compressed and sent (via CAN bus) to the remote receiving unit where they are reconstructed and retransmitted. It took a couple of weeks for me to perfect the code, but it works perfectly now with a barely perceptable pause between the press of the button and the reaction of the equipment. The most difficult part was decoding all the different signaling formats (actually sorting through the received code to determine if a lead in sequence is present, what is the 0 & 1 format, actually decoding the data that was sent, etc). I managed to come up with an algorithm that recognizes almost all the codes in a universal remote - save for the famous brand names I mentioned earlier.

Before you ask, no I can't share it. But a tip when it comes to transmitting the sequence (actually flashing the IR LED): use the PWM module to create a (approx) 40 kHz 50% duty cycle waveform - this drives the LED (or a transistor, which in turn drives the LED). Then write your code to switch the TRIS so that the PWM module gets connected to the LED to create the bursts, and disconnected to create the silences. Much better than using delays and output_high() and output_low() commands.

[Markdem]

Thank you for all your help guys.

I did not think of using a remote from another device that i dont have. The universal remote can be programed with predefinded sets of codes from the internet. So, what i am thinking i will do is take a device that i dont own eg. sony tv, and send the commands to my reciver that i will make. Then iwill make my reciver change the command from the remote, eg channel up, into a command i need, eg lights on.

Will this work??

Thanks again, Mark

[asmallri]

Yes it will work, I used this approach myself.
_________________
Regards, Andrew

http://www.brushelectronics.com/software
Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!!