RF filter required for 36KHz

[MikeBrady]

Thanks to everyone for their input on this. Lots of good ideas, some of which I'm just about capable of carrying out...

One of the things I was doing wrong, that I now realise from the forum responses, was that I was just measuring the o/p from the IR sensor using a simple voltmeter. Of course, it seems really obvious now, but I really should have been using my scope. I'll have a go with that over the weekend and see what that shows up.

Anyhow, I am still VERY interested in being able to build a circuit that can filter out the 36KHz frequency being emitted by the IR diode. So far no-one has posted any circuit ideas, or component values that might help me to build this. Yes, I know I can build my detector in other ways, but this stuff really fascinates me, so I am using this 'project' as a learning vehicle.

I'd really love to be able to build a receiver circuit that I could connect my scope to and see a reconstructed waveform, so that if I were sending a 36KHz IR signal, which was turned on and off regularly and which generated a waveform similar to the attached image https://www.electro-tech-online.com/attachments/crotracea-jpg.29674/ then I'd be able to 'see' a very similar waveform appear on my scope attached to the receiver circuit.

Unless I have completely misunderstood the requirements of the receiver, then I reckon all I need is a suitable circuit that can filter out all/most of the other spurious IR signals, and just concentrate on the 36KHz one.

Like I said earlier in the thread, I think it would consist of a simple amplifier followed by a filter (or vice versa).
However, I really don't know how to build the filter, i.e. what components and values to use so that it only passes 36KHz.

Any help in this area would be really appreciated.

 

[Nigel Goodwin]

Anyhow, I am still VERY interested in being able to build a circuit that can filter out the 36KHz frequency being emitted by the IR diode. So far no-one has posted any circuit ideas, or component values that might help me to build this. Yes, I know I can build my detector in other ways, but this stuff really fascinates me, so I am using this 'project' as a learning vehicle.

The reason no one has posted any such circuit, is that you don't need it if you use the simple three pin IC.

If you don't want to use one, but build your own - it's quite difficult and complicated, requiring multiple opamps and a VERY critical layout, with instability and oscillation a serious concern - and it's very unlikely to perform as well as the simple three pin ones.

 

[MikeBrady]

Change reference voltage of square wave

I managed to spend some time on this project over the weekend, and got very good results from the ZD1952. As I indicated in an earlier append, I was (incorrectly) trying to measure signals/output on the ZD1952 (https://www.jaycar.com.au/products_uploaded/ZD-1952.pdf) using a voltmeter. Once I used my CRO, it became obvious that the receiver was doing its job, and more importantly, it was receiving a very clear signal from my IR transmitter circuit. For me this was a real Eureka moment!

I now have another question that I think will be very easy to answer.

What I am getting on my output pin of the ZD192 is a very clear square wave signal which corresponds to the 800ms pulses I am sending from my transmitter. However, instead of being between 0 and 5V which is what I would like, they are from -3 to 2V.

Question: What sort of circuit do I need to change the bottom of the square wave from -3V to 0V (and the top of the square from 2 to 5V)? In other words, I need to somehow rebase the wave with 0 volts as reference.

 

[fvnktion]

I have started looking into a design to do the same thing, but at a range of frequencies from 9khz up to hundreds of khz.

If you don't want to use one, but build your own - it's quite difficult and complicated, requiring multiple opamps and a VERY critical layout, with instability and oscillation a serious concern - and it's very unlikely to perform as well as the simple three pin ones.

Rather than discourage from building why not give some tips on getting started??

I found a link to somewho has has quite a few circuits that are demodulating with discrete components. Circuit - SINGLE IC FORMS SENSITIVE MODULATED LIGHT RECEIVER - Circuits designed by David A. Johnson, P.E. . I am not familiar with such a high inductor feedback that he seem to be using here.

I have also thought about using a tone decoder IC to decode a digital pulse train. I am also looking into using a bandpass filter followed by an integrator to demodulate the pulses. You many want to see my post where I am asking about these things.

Best of luck!

 

[MikeBrady]

Thanks for the helpful links fvnktion. I agree with your comments 110% - I was a bit put off by the lack of positive advice - all I wanted was some basic hints and tips to get me started down the right track. For me, this is as much about learning as it is creating something functional. I may well end up using the pre-built IR filter, but I'd also like to know what principles and components go into making up an example circuit. I really do appreciate you taking the time to add your comments.

 

[Nigel Goodwin]

I have started looking into a design to do the same thing, but at a range of frequencies from 9khz up to hundreds of khz.

If you're using IR for something totally different, then you obviously can't use TSOP's, they are specifically designed for one purpose, and you need to bear in mind their limitations. But within those limitations, they can't be touched.

Rather than discourage from building why not give some tips on getting started??

I gave a tip - DON'T DO IT!

Three pin IR receivers are cheap and out perform anything you're reasonably going to build.

My experience pre-dates IR remotes, so I've followed their development throughout their live - and until reliable IC versions came about they were complicated and often fraught with problems. The previous best used specific IC's fed from photo-diodes, in fully screened metal cans, but the IC's are long since discontinued - and the TSOP's are far better anyway.

I found a link to somewho has has quite a few circuits that are demodulating with discrete components. Circuit - SINGLE IC FORMS SENSITIVE MODULATED LIGHT RECEIVER - Circuits designed by David A. Johnson, P.E. . I am not familiar with such a high inductor feedback that he seem to be using here.

And it looks a really poor low quality design, likely to have a short range, and be plagued by any local interference.

 

[fvnktion]

Here is another circuit built and tested by a student to do this function. It uses a band pass filter and demodulates with a 555 timer. You may want to use a micro rather using the 555 timer and all the discrete logic.

Like Nigel said, I'm sure none of these options will perform as well the IC versions, but you'll learn a wealth of information in the process and have fun doing it.

https://www.electro-tech-online.com/custompdfs/2009/07/Nabil_IR_Remote_Control_Demodulation.pdf