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

[Luc]

You could try it with the cable between PCB and PC but not between PCB and receiver, there will probably be too much disturbances.

I would not recommend to use a cable that long between PC and UIRT, it can work but will it be reliable? The best solution would be to convert the UIRT signals to proper RS232 using a MAX232 or equivalent.

[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

[Luc]

The UIRT supplies the comm port with levels of 0 and +5V.
The standard RS232 uses -12V and +12V.
This doesn't create problems because for almost all RS232 ports a low is everything below +2V and everything above this is considered as high.

The MAX232 only converts the UIRT levels to RS232 levels using a single 5V supply and does nothing with the data.

There was somebody else mentioning this in the forum, maybe he can help you out as he might have succeeded. Otherwise I could try to make a drawing but it involves 2 IC's and other components, not THAT simple..

[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/viewtopic.php?t=2049&highlight=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.

[windtrader]

Vynce,

I am using a UIRT2B (internal) with a 25 ft shielded 24 gauge six conductor cable for the the emitter and receiver signals. One end uses the supplied plugs and jacks that connect to the PCB, the other end has the two emitters attached to one pair of the cable and the receiver, cap, and ferrite core soldered to three other wires.

The cable runs from the HTPC down the back of an equipment rack jammed with all kinds of low and high power cables, under the floor into another room, up the wall into a bookcase where I mounted the emitters and receiver.

So far, things are working fine. On the commands I have fully configured, the signal seems quite reliable. Also, after I "tuned up" the orientation of the emitters and receiver, the signal improved.

I am using the recommended ferrite and cap mod. It made a HUGE difference for me. Look at the external connections/connecting the IR receiver section of the web guide. Go to the following forum topic for the link.

http://www.girder.nl/phpBB2/viewtopic.php?t=2189

Don

[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.

[windtrader]

vynce,

Glad it worked! How long a Cat5 cable did you end up running between the PCB and receiver? What does the cable travel by along its length that could cause noise or interference?

Are you using the IR Debug function in the UIRT2 plugin? I thought there was a function that listed out the codes not just the bar?

FYI - My unit running shielded cable is operating perfectly. I did add another set of emitters using 20 ft. of cat5 and emitters with a different spec than the original. I was a bit concerned that it might not work but it seems to work at least at short range. The spec states 2.1V @ 50mA 940nm T1 - 3/4 (5mm). They are clear, not blue.

Don

[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 :).

[krbuck]

I just want to be sure I understand what I'm doing before I start desoldering/soldering my brand new UIRT2A's IR receiver.

I want to mount the receiving component about 25 feet (about 7.5 meters) from my HTPC. All my emitters will be mounted near the PCB, so they don't need to be remote to the PCB. The only thing I need moved is the receiver.

How does this sound?

1. Carefully desolder the IR receiver from the board, leaving the LC circuit intact on the PCB.
2. Solder three leads of a cat5 pigtail cable directly to the PCB and mount the PCB using some suitable strain relief.
3. Connect the 7.5 meter cat5 cable to the short length via a connector and run it out to where I want to mount the receiver.
4. Mount the reciever, solder the appropriate leads to the cable using a strain relief.
5. Test.

Will this work?

Many thanks! --Karl

[vynce]

I have a ~7m unshielded CAT5 cable between the UIRT2 PCB and the receiver/transmitters and it has worked perfectly for the last few months. I haven't had any problems due to interference. The only difference that I see between what you're planning to do and what I have done is that I have the LC filter at the receiver end of the cable.

UIRT2B-------Long Cable-------LC--Receiver
in PC \____Transmitters

There are two 3.5mm stereo audio plugs on each end of the cable. One end of the cable plugs into the UIRT2B the other end plugs into a box that houses the receiver and transmitter. I think I had each data line twisted with a ground - so data from the receiver was twisted with ground from the receiver, etc. Using a shielded cable would work even better (or even a fiber optic cable :lol: ).

[krbuck]

vynce,

Many thanks for the response. This is exactly the confirmation of my approach I needed.

Now I just have a serial, component and svideo cable to figure out, and I'll be all set. =)

Cheers. --Karl

[izone]

"1. Carefully desolder the IR receiver from the board, leaving the LC circuit intact on the PCB. "

The L-C filter should be as close to the IR Rx module as possible.