Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: chris on 02/10/2015 08:44:47
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Why would an infrared TV remote work at night but not in the day? A listener to the radio show said he had this problem: he needed to be in direct line of sight between the remote and receiver in the daytime but not at night. What do you think? I suggested extraneous sources of infrared in one situation but not in the other.
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I think you are right. The receiver might be using automatic gain control (agc) to reduce interference. As you say there will be a lot of natural IR around in the day raising the noise level and causing the receiver to reduce it's sensitivity and putting reflected signals from the controller into the noise zone. At night, less noise, sensitivity increases and able to detect reflected signals.
There are other possible explanations but without seeing the circuitry and spec for the sensor/transmitter it is hard to be certain
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If direct Sunlight is hitting the infra-red receiver, that would make it much less sensitive.
It could also be caused by a reflection of infra-red light from the Sun, such as bouncing off a sheet of glass.
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Cheap batteries , carrier signal being washed out by ambient noise?
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I think our suggestion of a masking effect owing to high relative intensity of infrared in the incoming sunlight is the reason.
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The IR receiver has to recognise a coded signal. If there is a high background intensity of "noise" from sunlight, the signal/noise ratio will be insufficient to provide a reliable decode and the system will default to "off". But sometimes they don't, and people complain about a haunted television.