Author Topic: IR Demodulation with non-standard frequency 8Khz and 5Khz  (Read 910 times)

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Offline rx8pilotTopic starter

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IR Demodulation with non-standard frequency 8Khz and 5Khz
« on: September 03, 2019, 10:23:01 pm »
Hello all.....

I am trying to make a circuit to monitor data from an industrial sensor system that uses IR to communicate. It operates at an unusual 8khz and 5khz modulation scheme so I cannot use the ubiquitous Vishay TSOP units that have all the delicate analog elements sorted out in a 3pin package.

https://www.vishay.com/docs/80069/circuit.pdf

The idea of replicating what is inside the Vishay units (or similar) is not trivial and perhaps likely to end up being fairly large final circuit with quite a few discreet components. Perhaps I can go small on the analog side by simply using a PIN diode that feeds a transimpedance amplifier and sending that direct to an ADC where the rest can be processed in microcontroller firmware. The DSP/demodulation can be done on a microcontroller.

Does anyone have any suggestions on how this problem can be approached in the simplest way? The only IR I have every done uses typical carrier frequencies making the circuit design trivial. Dreaming there is a chip solution that I just have not yet found.

Additional notes:
Short distance, relatively high IR power. The environment is fairly protected from IR noise. It is preferred to make the end solution a battery-powered circuit, so low power is desirable.

Any advice is greatly appreciated.
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Offline David Hess

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Re: IR Demodulation with non-standard frequency 8Khz and 5Khz
« Reply #1 on: September 04, 2019, 03:06:29 am »
The Analog Devices LT1328 may be suitable for the signal conditioning part.  Linear Technology used to make quite a few IR receiver ASICs so you may want to go through their products.
 

Offline rx8pilotTopic starter

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Re: IR Demodulation with non-standard frequency 8Khz and 5Khz
« Reply #2 on: September 04, 2019, 03:31:44 am »
The Analog Devices LT1328 may be suitable for the signal conditioning part.  Linear Technology used to make quite a few IR receiver ASICs so you may want to go through their products.

That LT1328 looks like it will save some design time and board space for the front end - likely providing enough conditioning to do the rest in software. Good suggestion! I am looking deeper into the Linear parts, did not even think of them until now.
Availability looks good, I will layout one of these on my dev board.

Thanks!
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Re: IR Demodulation with non-standard frequency 8Khz and 5Khz
« Reply #3 on: September 04, 2019, 03:40:47 am »
QSE257 and similar work well for short range reception. Does not do demod - you get the carrier.

https://www.mouser.com/datasheet/2/308/QSE257-1307001.pdf
 

Offline rx8pilotTopic starter

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Re: IR Demodulation with non-standard frequency 8Khz and 5Khz
« Reply #4 on: September 04, 2019, 04:10:41 am »
QSE257 and similar work well for short range reception. Does not do demod - you get the carrier.

https://www.mouser.com/datasheet/2/308/QSE257-1307001.pdf

The big dream is a bandpass filter for good noise rejection that can be programmed with external components. Maybe a bit of an ask. The linear part has a highpass filter that is externally programmable - which is a start I guess.
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Offline rx8pilotTopic starter

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Re: IR Demodulation with non-standard frequency 8Khz and 5Khz
« Reply #5 on: September 05, 2019, 06:50:49 pm »
So, I have started a development design.

Essentially, I am looking to use the Vishay block diagram for the popular TSOP parts as a starting point.


Transimpedance amplifier - got it, no problem.
Bandpass filter - got it, no problem.
Schmitt Trigger - got, no problem.

The part that I do not have an immediate solution for is the AUTOMATIC THRESHOLD CONTROL  for the Schmitt trigger. It serves an important function for sure, but I am unsure how to best implement that (at least in a reasonably simple fashion).
« Last Edit: September 05, 2019, 06:55:07 pm by rx8pilot »
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