Extendng the reach of the USB-UIRT using IR blocks

[loo_hoo_ser]

Hi y'all -

I was able to extend the reach of the USB-UIRT device by using a Cat-5E cable and an IR terminating block. I'm including a writeup with pictures on how I did this so that it helps others that are interested in doing this.

Right now, this only works one-way (IR blaster) because the USB-UIRT does not have a jack to connect into for receiving IR signals.

As I mentioned in the writeup, it may be possible to modify the USB-UIRT to include a jack for an IR receiver and extend that over the same cat-5e cable.

The main advantage of doing this is that it allows the Housebot PC remain n a separate location where the gear being controlled IR is located. Also, with multiple USB-UIRT's, it is possible to create multiple IR zones with one HB server and multiple cable runs (and multiple IR terminating blocks as well).

Just one caveat - proceed at your own risk. I take no responsibility for errors or omissions leading to damaged hardware.

Enjoy.

[Richard Naninck]

Not sure I am following this correctly, but your solution seems overly expensive.

In the pictures I see your USB UIRT connected directly to the PC. So no cat5 extension there. You extend the IR outputs using cat5 and some hardware. My question is; why would you do that while a two wire cable with no blaster features at all, a 50 cent IR led and a small resistor in line will do the same thing. I have both IR outputs connected to the UIRT and they extend to over 25 meters of length with just a two wire cable, a LED and a resistor. One of the two LEDs is positioned about 4 meters in front of all the media equipment and it is powerfull enough to reach it all and shine through matted glass.

Unless of course your house is prewired with cat5, but still you could do without the blaster.

Still you need somekind of IR repeater for the input (like you said).

[loo_hoo_ser]

Richard -

I agree, I thought it was somewhat expensive too - the AT termination block was pricey and so was the IRE-5.0 blaster. However, it can be done more cheaply by using a passive terminator (that still has some active circuitry). One can be found here at Smarthome:

http://www.smarthome.com/97252524.html

and along with an IRE-3.0 IR emitter (also at Smarthome).

Regarding your approach, I did some back-of-the-napkin calculations. Assuming that one uses a wiring of 26 AWG for the two wire runs for the IR LED, the solid conductor 26 AWG which is found in Cat-5E cabling has a resistive loss of 43.6 ohms per thousand feet. (link here: http://www.thelenchannel.com/1wire.php). Your estimated wiring run legnth has 25 meters which comes to 82 feet per leg (one leg to the signal source, one leg for the return path), for a total of 164 feet. That corresponds to a DC resistive loss of 7.15 ohms (164 ft/1000 ft * 43.6 ohms/ft).

Assuming you are using a 150 mA current drive to drive your IR LED to get the blast effect(assuming it can handle the current). The USB-UIRT cannot produce a voltage higher than 5V at its IR jack output because it's a self powered USB device which has 5V power only. An LED requires approximately 1.7 volts to operate, which requires an in-line resistor to drop roughly 3.3 volts (to get the 5 volts down to 1.7 volts). For 150 mA and no resistive wiring loss, the the value of the in-line resistor comes to 22 ohms. However, due to resistive loss of the 160 feet of the wiring, this adds about 7 ohms of resistance to the LED circuit. Thus, the resistance is effectively 29 ohms and the LED drive current drives drops down to 113 mA instead of the desired 150 mA. This means the IR LED would not be as bright as desired. However, this can be overcome by decreasing the value of the 22 ohm resistor to 15 ohms to compensate.

Consider instead, if the wiring run were 500 feet. This comes to a total of 1000 feet of wiring totaling 43.6 ohms of resistance in the circuit. There is no way to compensate for this. Assuming the in-line resistor were zero ohms for this cable run, the current drive would only be 76 mA, which is less than half of the desired 150 mA and thus making the IR LED half as bright. So, the IR signal output from the USB-UIRT must be captured and the IR blaster LED must be driven with a separate drive circuit because there is no current drive capability remaining in the long wiring run after accounting for resistance loss.

Your solution works fine for relatively short cable runs. I just didn't know how much current drive the USB-UIRT was capable of, so I decided it was better to buffer (repeat) the signal. I do know that it cannot be more than 500 mA since that is the limit for a self powered USB device. Some of that current has to drive the USB interface and the microcontroller. Some of it has to drive the built in IR emitter and the red indicator LED. So, that doesn't leave a whole lot of current drive for the IR output on the phono jack.

The other problem was, I didn't know how strong of an IR output the IRE-3.0 was capable of, so I wanted to use the IRE-5.0 blaster which has more IR output, but requires a much stronger drive strength, which requires using the AT-1.0 active terminator which is specifically designed to handle high current drive for IR blaster.

So, yes, it can be done differently and more cheaply. There is more than one way to do this.

I think the solution I described above is a good choice for driving the IR signal over really long wiring runs and provide multiple blaster outputs at the destination. The AT-1.0 terminating block can be used to drive two IR blasters and two IR emitters as needed.

This will help those who have a need to drive the signal reliably over long runs.

YMMV.

[Richard Naninck]

Well, I just went ahead and built it and came to the conclusion it worked. Although I know all of these calculations, I didn't do them. I had my own IR blaster hardware before I bought the UIRT and just used the sending LEDS from that system. As for the inputs, I used the 5 volt based IR receivers from Siemens. +5V, Gnd and Data.

Question; what range are you extending to?