Cable Length

[vynce]

I need to be able to use a UIRT between two rooms. It needs to receive IR in a room downstairs and will be connected to a computer in another room upstairs. This requires a cable about 10 meters (33 feet) long. I currently use a LIRC-compatible device (Igor's plugin) with this length of CAT5 ethernet cable and it works fine. The long cable is between the COM port and the circuit board.

I would like to upgrade this to a UIRT2 though and was wondering how cable length would affect this device and where the best place would be to place the long cable. Would it be best to place the long cable between the COM port and the circuit board, or between the circuit board and the IR receiver? If I place the long cable between the circuit board and the IR receiver would it be best to have the L-C filter closer to the IR receiver or closer to the circuit board?

I may just need to do some experimenting to see what works best, but I thought I would ask first in case anyone knows about this stuff.

Thanks

[vynce]

How would converting the UIRT signals to RS232 help? Does RS232 contain CRC information or something? I guess the UIRT plugin wouldn't work then, so I'd have to use the serial plugin (?).

I haven't designed any circuits before, so I'm not sure I could implement the MAX232 properly.

Thanks

[vynce]

I see. So it basically increases the signal strength so that there is less signal degredation over a longer cable. Sounds good to me . unimatrix is the one who used a MAX232 in his UIRT (http://www.girder.nl/phpBB2/viewtopi...ghlight=max232). I'll try contacting him to see if he can help.

[levyshay]

Hi, If you read his thread you'll notice that the MAX232 inverts the RS232 levels. While this is usually not a problem when you write your own firmware (because you can invert them by software), you'll have a problem here.
I suggest 1st trying as it is to see if it works, If it doesn't you can try programming your UIRT with UIR firmware, since UIR uses 9600bps instead of 115200 it might work (as I understand you don't need transmitting IR commands only receiving)

And another idea came to my mind (I'm not sure if it can be done, haven't test it / looked at MAX232 datasheet lately ) is putting one MAX232 near the UIRT and one near the PC so You'll get MAX232 converting to RS232 levels then another one converting back to logic levels ( 0 / 5v ) and since the UIRT already worked with logic levels it should work now, also by this the signals shouldn't get inverted.

Shay Levy.

[jediperry]

You can just put not gates on the rx & tx lines between the max232 and the pic. Obviously the 2 gates would be going in the oposite direction to each other.

Mike.

[vynce]

Yes, I think I will try it without any modifications first. If it doesn't work I'll start playing with things . I don't need to transmit right now, but I would like to be able to use that feature eventually. Thanks for all the info/ideas.

[vynce]

Thanks for the info. Looks like I'm going to have to do a lot of experimenting . I really would like to have the long cable between the PCB and the receiver/transmitters if possible. I might have to switch from an unshielded ethernet cable to some kind of shielded cable to get it to work though.

[vynce]

Here is an update on this. I have the long CAT5 cable between the pcb and the receiver/transmitter and it works fine. The L-C filter is connected directly to the receiver and makes a huge difference. Using the IR debug function in the UIRT driver I can see that it does receive some false data, but very little - it would probably take an hour or more for the blue bar to go all the way across.

[vynce]

I just measured the cable and it is around 6.5 meters (22 feet) long (a bit shorter than I had guessed in my first post). The cable runs past all the cables from the back of my PC (several of them are power cables), then through the floor with several ethernet cables to downstairs. I might try wrapping some grounded alumin(i)um foil around the part of the cable that runs next to the power cables.

Yes, I'm using the IR Debug function of the UIRT2 plugin. It does show the codes after the bar has reached the right-hand side of the box. But, the bar moves so slowly that I didn't want to wait for it to reach the other side.

I haven't tested the transmitters yet.

[vynce]

Well, I left it sitting at the IR Debug screen and it took 15 minutes for the blue bar to get right across. Here is the data that was output after that:

BB AF 04 FF 
C3 82 04 FF 
D9 F2 04 FF 
AA 52 04 FF 
6D E2 04 FF 
DF 62 04 FF 
38 72 04 FF 
4D E2 04 FF 
A4 A2 04 FF 
BE B2 04 FF 
25 22 04 FF 
32 C2 04 FF 
22 02 04 FF 
28 62 04 FF 
80 22 04 FF 
A3 42 04 FF 
DA 32 04 FF 
94 A2 04 FF 
FA 72 04 FF 
DE A2 04 FF

These interference codes are much shorter than real IR codes like this:

02 72 42 41 11 0F 11 30 11 0F 11 0F 11 30 11 30 11 30 11 0F 11 30 11 30 11 0F 11 30 11 30 11 0F 11 30 11 30 11 0F 11 0F 11 0F 11 30 11 0F 11 0F 11 30 11 0F 11 FF

So overall I don't think it will cause any problems. Of course it would be nice if it didn't ever pick up any interference .