TV remote IR receiver module
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From: pawihte on 26 Nov 2009 02:30 Are TV IR remote control receiver modules frequency selective? I know that remote control systems use PWM and the pulses are decoded by a microprocessor. What I would like to know is whether the module that functions as the IR photosensor, amplifier and pulse shaper is usually tuned to a particular carrier frequency so that they are not all interchangeable (aside from things like pin-out, pulse polarity, etc.). If this is so, how sharply are they tuned? Is it likely that a receiver tuned to, say 38 kHz, will respond well to 36 or 40 kHz emissions?
From: Rich Webb on 26 Nov 2009 07:08 On Thu, 26 Nov 2009 13:00:33 +0530, "pawihte" <pawihte(a)invalid.com> wrote: >Are TV IR remote control receiver modules frequency selective? I >know that remote control systems use PWM and the pulses are >decoded by a microprocessor. What I would like to know is whether >the module that functions as the IR photosensor, amplifier and >pulse shaper is usually tuned to a particular carrier frequency >so that they are not all interchangeable (aside from things like >pin-out, pulse polarity, etc.). > >If this is so, how sharply are they tuned? Is it likely that a >receiver tuned to, say 38 kHz, will respond well to 36 or 40 kHz >emissions? Generally, the 3 dB down points of these are at about +/- 2 KHz so yes, you'll get a response with a 36 KHz signal using a 38 KHz module. -- Rich Webb Norfolk, VA
From: Hammy on 26 Nov 2009 07:39 On Thu, 26 Nov 2009 13:00:33 +0530, "pawihte" <pawihte(a)invalid.com> wrote: >Are TV IR remote control receiver modules frequency selective? I >know that remote control systems use PWM and the pulses are >decoded by a microprocessor. What I would like to know is whether >the module that functions as the IR photosensor, amplifier and >pulse shaper is usually tuned to a particular carrier frequency >so that they are not all interchangeable (aside from things like >pin-out, pulse polarity, etc.). > >If this is so, how sharply are they tuned? Is it likely that a >receiver tuned to, say 38 kHz, will respond well to 36 or 40 kHz >emissions? > They have an integrated band pass filter with a narrow passband. Here is a picture of a Panasonic detectors sensitivity versus fc. http://i50.tinypic.com/zn4u4h.png It may work but at a minimum you will have a reduced range. Sensitivity for the 38kHz Panasonic is reduced to about 54% typical at 36kHz. Other things to consider is they are also matched to specific wavelengths which is what the other graph shows. They also have specific data formats here's some from the TSOP348XX series. The data signal should fulfill the following conditions: o Carrier frequency should be close to center frequency of the bandpass (e.g. 38 kHz). o Burst length should be 10 cycles/burst or longer. o After each burst which is between 10 cycles and 70 cycles a gap time of at least 14 cycles is necessary. o For each burst which is longer than 1.8 ms a corresponding gap time is necessary at some time in the data stream. This gap time should be at least 4 times longer than the burst. o Up to 800 short bursts per second can be received continuously. It doesnt hurt to try if your just scavenging detectors and emitters.
From: pawihte on 26 Nov 2009 12:31 Hammy wrote: > On Thu, 26 Nov 2009 13:00:33 +0530, "pawihte" > <pawihte(a)invalid.com> > wrote: > >> Are TV IR remote control receiver modules frequency selective? >> I >> know that remote control systems use PWM and the pulses are >> decoded by a microprocessor. What I would like to know is >> whether >> the module that functions as the IR photosensor, amplifier and >> pulse shaper is usually tuned to a particular carrier >> frequency >> so that they are not all interchangeable (aside from things >> like >> pin-out, pulse polarity, etc.). >> >> If this is so, how sharply are they tuned? Is it likely that a >> receiver tuned to, say 38 kHz, will respond well to 36 or 40 >> kHz >> emissions? >> > They have an integrated band pass filter with a narrow > passband. Here > is a picture of a Panasonic detectors sensitivity versus fc. > > http://i50.tinypic.com/zn4u4h.png > > It may work but at a minimum you will have a reduced range. > Sensitivity for the 38kHz Panasonic is reduced to about 54% > typical at > 36kHz. > > Other things to consider is they are also matched to specific > wavelengths which is what the other graph shows. Thanks. This one appears to be intended for 940nm LEDs, with practically zero response to 850nm radiation. Are remote controls more or less standardised for 940nm? > They also have > specific data formats here's some from the TSOP348XX series. > > > The data signal should fulfill the following conditions: > o Carrier frequency should be close to center frequency > of the bandpass (e.g. 38 kHz). > o Burst length should be 10 cycles/burst or longer. > o After each burst which is between 10 cycles and 70 > cycles a gap time of at least 14 cycles is necessary. > o For each burst which is longer than 1.8 ms a corresponding > gap time is necessary at some time in the > data stream. This gap time should be at least 4 times > longer than the burst. > o Up to 800 short bursts per second can be received > continuously. > This seems to imply that it's not suitable for detection of a continuous emission with infrequent interruptions for applications like an intrusion detector or an event counter. Is that correct? > It doesnt hurt to try if your just scavenging detectors and > emitters.
From: pawihte on 26 Nov 2009 12:32
Rich Webb wrote: > On Thu, 26 Nov 2009 13:00:33 +0530, "pawihte" > <pawihte(a)invalid.com> > wrote: > >> Are TV IR remote control receiver modules frequency selective? >> I >> know that remote control systems use PWM and the pulses are >> decoded by a microprocessor. What I would like to know is >> whether >> the module that functions as the IR photosensor, amplifier and >> pulse shaper is usually tuned to a particular carrier >> frequency >> so that they are not all interchangeable (aside from things >> like >> pin-out, pulse polarity, etc.). >> >> If this is so, how sharply are they tuned? Is it likely that a >> receiver tuned to, say 38 kHz, will respond well to 36 or 40 >> kHz >> emissions? > > Generally, the 3 dB down points of these are at about +/- 2 KHz > so > yes, you'll get a response with a 36 KHz signal using a 38 KHz > module. Thanks. |