IR Demodulation with non-standard frequency 8Khz and 5Khz - Page 1
Forum section: electronics / projects

author: rx8pilot
author_rank: Super Contributor
timestamp: September 03, 2019, 10:23:01 pm
content: 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.pdfThe 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.

author: David Hess
author_rank: Super Contributor
timestamp: September 04, 2019, 03:06:29 am
content: 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.

author: rx8pilot
author_rank: Super Contributor
timestamp: September 04, 2019, 03:31:44 am
content: Quote from: David Hess on September 04, 2019, 03:06:29 amThat 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!

author: oPossum
author_rank: Super Contributor
timestamp: September 04, 2019, 03:40:47 am
content: 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

author: rx8pilot
author_rank: Super Contributor
timestamp: September 04, 2019, 04:10:41 am
content: Quote from: oPossum on September 04, 2019, 03:40:47 amThe 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.

author: rx8pilot
author_rank: Super Contributor
timestamp: September 05, 2019, 06:50:49 pm
content: 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).