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Because that's the frequency the receiver IC's use.
It came about because it was derived from the earlier ultrasonic remotes, which worked around that frequency.
can i transmit those signals other than 38Khz?
can i transmit those signals other than 38Khz?
Read this data sheet. I think the frequency selectivity of these receivers is much narrower than Nigel thinks.
The datasheet shows models that differ by 2kHz in carrier center frequency or less, implying that the selectivity is probably better than that.That datasheet makes no such suggestion?, as far as I'm aware the BPF in the chips is fairly wide and flat - the datasheet doesn't even mention it at all.
The datasheet shows models that differ by 2kHz in carrier center frequency or less, implying that the selectivity is probably better than that.
If they have a wide bandwidth, then why make models that differ by only 2kHz in center frequency?Yet no where does it suggest that - you're just making it up
Try them and see!.
If they have a wide bandwidth, then why make models that differ by only 2kHz in center frequency?
So it would appear that the units have different BP center frequencies, but the filter rolloff is not very steep, thus they will still operate well at other frequencies. It may be as you say, it only affects the maximum operating range slightly.I've always wondered that myself - like I said, try them and see - in my experience it makes not the slightest bit of difference, even at well over normal remote control ranges. I presume you will lose ultimate range by not accurately following the specified frequency?, but should you be trying to use IR at those distances?.
So it would appear that the units have different BP center frequencies, but the filter rolloff is not very steep, thus they will still operate well at other frequencies. It may be as you say, it only affects the maximum operating range slightly.
I don't have one to try, but it would make an interesting experiment.
Vishay makes IR recievers with different carrier frequencies. Like these...
30 kHz -TSOP34830
33 kHz -TSOP34833
36 kHz -TSOP34836
38 kHz -TSOP34838
40 kHz -TSOP34840
56 kHz -TSOP34856
Then they make a few with a wide range which could be used as an IR repeater like this one...
30 kHz to 50 kHz -TSOP98238
These are sold at Mouser.com
A 38.0 kHz IR receiver I was working with would work if the carrier frequency was in the neighborhood of 37500 Hz to 38500 Hz as I recall.
And would work better from 37800 Hz to 38200 Hz.
But would not work at 37 kHz or 39 kHz.