TSOP 31230-FREQUENCY DETECTION QUESTION-PROBLEM

Thread Starter

optus

Joined Oct 25, 2019
92
Hello

From my understanding this TSOP(from datasheet) should detect only 30 kHZ frequency,but i noticed when i point a TV remote control on it and push a button it also detect freuqency of 38 kHZ(TV remote frequency)-my green led lights up.Is this normal?? Is there possibility to prevent detecting signals of 38 kHZ, and detect only 30 kHZ??
I connected TSOP's leg 1 to ground,leg 2 to 5V. Leg 3 is connected to green LED,green LED is connected to 390 ohm resistor,and resistor is connected to 5V(series connection between leg 3 and 5V with resistor and LED)
 

ericgibbs

Joined Jan 29, 2010
10,058
hi optus,
Most TV remotes will enable the IR detect LED on the TV to flash.
The way the IR beam is encoded selects the required action on the TV.
E

Update:
Check this PDF.
 

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AlbertHall

Joined Jun 4, 2014
9,889
They are not that narrow bandwidth. See the graph below from the datasheet. At 1.3 times the centre frequency (39kHz) the sensitivity is about one fifth what it would be at 30kHz. This will reduce the range but not prevent reception.
1575022458671.png
 

AlbertHall

Joined Jun 4, 2014
9,889
Thank you
Is there any chance to prevent this?
I believe they are all similar and the filter is entirely internal so there is no opportunity to change it.
If you really, really want to you could make your own receiver from discrete parts but it would be difficult to match the performance of the integrated parts.
 

Papabravo

Joined Feb 24, 2006
13,754
The answer to your original question: "Is there possibility to prevent detecting signals of 38 kHZ, and detect only 30 kHZ", is an emphatic no. It is not possible to limit the detected range to a single frequency. The very best you can do is center the detectable bandwidth on a given frequency, e.g. 30 kHz, and live with whatever attenuation is achieved for frequencies on either side. It does help to quantify your requirements. For example, let us say that your requirement is to have a passband that is 6 kHz. wide, that is 30 kHz ± 3kHz where the attenuation at the band edge is say 20 dB. Furthermore the attenuation in the stopband, which begins at 38 kHz. must be greater than 60 dB. Now you have a defineable metric you can shoot for. You might wan to investigate optical IR filters, but I should warn you that they are not inexpensive.
 

Thread Starter

optus

Joined Oct 25, 2019
92
I believe they are all similar and the filter is entirely internal so there is no opportunity to change it.
If you really, really want to you could make your own receiver from discrete parts but it would be difficult to match the performance of the integrated parts.
Thank you
 

Thread Starter

optus

Joined Oct 25, 2019
92
The answer to your original question: "Is there possibility to prevent detecting signals of 38 kHZ, and detect only 30 kHZ", is an emphatic no. It is not possible to limit the detected range to a single frequency. The very best you can do is center the detectable bandwidth on a given frequency, e.g. 30 kHz, and live with whatever attenuation is achieved for frequencies on either side. It does help to quantify your requirements. For example, let us say that your requirement is to have a passband that is 6 kHz. wide, that is 30 kHz ± 3kHz where the attenuation at the band edge is say 20 dB. Furthermore the attenuation in the stopband, which begins at 38 kHz. must be greater than 60 dB. Now you have a defineable metric you can shoot for. You might wan to investigate optical IR filters, but I should warn you that they are not inexpensive.
Thank you
 

Papabravo

Joined Feb 24, 2006
13,754
An optical filter won't change the response to the modulation frequency though.
That is true, but it will change the response to the frequency of the IR LED in the TV remote, which won't be much help if the TS uses the same IR LED as in the TV remote. If you want to concentrate on the modulated signal, digital filtering might be possible if you have some way of limiting the input bandwidth in the analog domain. In other words you need an analog anti-aliasing filter in order for digital filtering to work.
 
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BobTPH

Joined Jun 5, 2013
2,396
You could place a 38 KHz TSOP next to it and use its output to disable the output of your 30KHz one. You would want to use a monostable to extend the disable pulses since they would not exactly correspond to the pulses from your detector.

Bob
 

AlbertHall

Joined Jun 4, 2014
9,889
You could place a 38 KHz TSOP next to it and use its output to disable the output of your 30KHz one. You would want to use a monostable to extend the disable pulses since they would not exactly correspond to the pulses from your detector.

Bob
But the 38kHz sensor would also respond the 30kHz modulated signal so the output would be always disabled.
 
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