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Trouble with IR repeater

 
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utmba95



Joined: 15 Nov 2003
Posts: 40
Location: Austin, TX

                    
PostPosted: Wed Jun 23, 2010 3:38 pm    Post subject: Trouble with IR repeater Reply with quote

I built an IR repeater by taking the super sensitive IR detector out of my old Tivo and modulating the signal with a 555 timer. It works great for the most part and now allows me to control my HK receiver from across the room rather than just 10 feet away.

I am seeing something weird though. My DirecTV HR2x DVR sometimes ignores key presses from my URC-6131 w/extender. It seems like short key presses are most likely to be missed, but it's hard to tell because the DVR is not very responsive. It also seems like the OEM remote doesn't have this problem.

I'm going to order a learning remote or an IR widget to see exactly what the difference is between the OEM remote and the URC-6131 with and without the repeater. In the mean time, is there anything simple you can recommend I try? I haven't updated anything in the remote for a couple of years, so perhaps there is something I should try updating.
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utmba95



Joined: 15 Nov 2003
Posts: 40
Location: Austin, TX

                    
PostPosted: Tue Jun 29, 2010 3:44 pm    Post subject: Reply with quote

I got my IR Widget and it turns out my carrier frequency isn't accurate enough. My DirecTV box won't respond well to anything much less than 38 KHz, and my Harmon Kardon receiver won't respond well to anything much more than 38 KHz. The 555 timer frequency drifts over temperature and is difficult if not impossible to keep in a range where both are happy. I may have to switch to a crystal oscillator.
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The Robman
Site Owner


Joined: 01 Aug 2003
Posts: 21210
Location: Chicago, IL

                    
PostPosted: Tue Jun 29, 2010 5:08 pm    Post subject: Reply with quote

Can't you tweak the upgrades so that the DirecTV signal is greater than 38kHz and the H/K is less than 38 kHz *, so that even if the repeater alters their frequency, it won't take them out of range.

* This would require using a protocol upgrade for each and tweaking the carrier frequency there. If you don't know how to do that, ask.
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Rob
www.hifi-remote.com
Please don't PM me with remote questions, post them in the forums so all the experts can help!
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cauer29



Joined: 03 Feb 2010
Posts: 236

                    
PostPosted: Tue Jun 29, 2010 9:40 pm    Post subject: Reply with quote

utmba95 wrote:
I got my IR Widget and it turns out my carrier frequency isn't accurate enough. My DirecTV box won't respond well to anything much less than 38 KHz, and my Harmon Kardon receiver won't respond well to anything much more than 38 KHz. The 555 timer frequency drifts over temperature and is difficult if not impossible to keep in a range where both are happy. I may have to switch to a crystal oscillator.


If I understand correctly what you've done, you salvaged a detector IC from an old Tivo and this detector outputs baseband demodulated envelope of the detected IR signal. Then you take this output and use it to gate the 555 running at ~38 KHz on/off driving an IR LED to recreate the original IR signal. Of course, the detector you're using only gives the on/off of the overall bursts and not for each pulse of IR detected and so you lose the original frequency info. You've now discovered why the commercial repeaters do not do it that way. They replicate each and every IR pulse exactly recreating the original signal frequency. That said, I did once make the same type IR repeater. It's much easier if you use a commercially available modulator such as this one:

http://www.rentron.com/remote_control/TX-IR.htm

This one will hit 38 KHz right on the money with negligible drift and is configurable for active high vs active low input level and can also be configured for 40 KHz output.

A.A.
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