17th June 2012, 05:24 PM
Automated Home Guru
Strange things happening with ITR
The ITR module in our lounge appears to be being affected by our TV.
I know this sounds very strange but when the screen is showing a blue screen, imagine Sky's main theme colours, the LED on the ITR starts to flash very erratically so much that the ITR doesn't recognise anything being sent to it.
We found this to be a problem yesterday when SWMBO wanted to watch something she had saved on Sky. The screen asking for the PIN is all blue with a small amount of white text in the middle. As our ITR relays frames to another ITR at Node 0 where the SKY boxes are we lose all control over SKY. If we turn the TV off then the flashing stops and Sky can be controlled again.
I've now sat and watched the ITR and depending what is on the screen depends on how much the LED flashes. We turned off PIN rescritions yesterday to circumvent the problem but discovered today that if you want to watch a pre watershed program / movie then, by law, you have to enter a pin. So back to square one.
I doubt if anybody else is experiencing this problem, as it's very unique, but if there is anybody I'd like to know how you are dealing with it.
18th June 2012, 11:35 PM
Automated Home Jr Member
My Sony bravia when switched to any channel throws out random IR all the time. I have an ITR on the wall near it and the led happily flashes away whilst we're watching telly.
I've got an old Pace remote control from a long-since thrown away freeview box that I use as a remote for the room and side lights etc.. and unless you point that directly at the ITR when the telly is on, it doesn't always get through the 'chatter'.
19th June 2012, 01:32 AM
Automated Home Legend
Seems to be variable. A test also with a Sony Bravia LCD TV with ITR about 1 meter away facing screen shows chatter but only for certain displays - for example blank display when input is directed to (non existent) PC input doesn't cause any chatter whereas blank display when input set to AV1 or other such does. On TV channels which have pictures no chatter but if on a TV channel which is not transmitting get chatter. The chatter is definitely caused by optical noise. It is not unknown that LCD and plasma displays create IR noise but, as in this test, seems not the same for all states or TVs. Don't know exactly why. Backlighting LEDs and plasma will I guess extend sufficient power into near infra red regions which IR remotes typically use (940nm), however this in itself is not necessarily a cause for chatter since the IR receiver is bandpass filtered optically and also for carrier frequency and also for pulse widths. So what this would suggest is that under certain conditions TVs must be modulating the backlighting (it does seem to be the blank area in the test we conducted) at a frequency close to the pass band and in a similar pulse width to IR data. Short of changing the way the TV or IR receiver device work I think the only practical solution at present is to reduce the ability of the ITR to 'see' the TV screen or its reflections relative to its ability to see the remote handset. If relocation is not possible then could be that some extra optical shielding might cut down the emissions from the TV sufficiently relative to the power delivered by a handset which might be pointed directly and perhaps more closely at the ITR. In our own test another ITR about 3 meters away looking sideways at the TV had no problems receiving and executing IR commands from a handset during the chatter periods suffered by the closer ITR. Optical shileding might consist of a 'blinker' type arrangement if the TV is to one side and reflections are weak or it could be some further occlusion of the middle of the IR window behind which the receiver is located. You might even try a piece of black electrical tape - some black looking media still pass through some IR...
19th June 2012, 09:04 AM
Automated Home Legend
we found the IR on our old hi-fi is prone to chatter from older CFLs (older types & well-used), becoming unreliable as a consequence .... but we thought newer IR codes gave good immunity to such things ...
how about being (optionally) more restrictive about what Cortex passes-on ?
19th June 2012, 11:12 AM
Automated Home Legend
Its not done in Cortex but rather by the module itself.
In addition to the various stages of filtering provided by the optics and the receiver device itself there is also filtering in the module code too, such that for example very short pulse bursts are rejected and conversely that some tolerance is applied to slight variations in pulse widths, but it is difficult to try and cater for as wide a range of formats whilst rejecting what might be noise. The problem here is that if the noise gets past the initial filtering it will basically be additive to legitimate signals coming in at the same time so without prior knowledge it would be difficult to determine and strip away the noise part - since rejection of the entire signal would not achieve the desired result.