Help on infrared remote control, 38khz quarz

They're not extremely hard to get - take apart practically any TV/VCR/DVD/universal remote control and you'll find a crystal (actually a ceramic resonator) of approximately this frequency.

Most of remotes use a RC oscillator of some kind to set the frequency. You will note that the tutorial example circuit uses a quartz for the transmitter but a RC for the receiver.

Many homebrew microprocessor-based IR remote projects use a microprocessor clocked in the MHz range and divide down (often in software delay loops) to get to the actual data rate.

If you want to use a crystal in the transmitter, go ahead and use a

32.768 kHz crystal and modify the RC constant in the receiver appropriately.

Tim.

Most [infra-red] remotes use a ceramic resonator to set the frequency.

Yeah well I read what the website says, but the problem is that there is no German electronics company that sells ANYTHING near that range. The only crystals they have are xx MHz, not kHz. If I look for crystals in some old TV remotes, I'll probably find crystals, but I don't know what frequency they are...besides the fact that I don't even have an idea what a crystal looks like.

But thanks for all the responses so far anyway.

Greetings

Well thanks, that sounds like it could work. The only problem is, I hate to say this, but I have no clue on how to build something like this, so if you happen to know any knowledge source where I could find some guides on this, I'd be happy to know. I have this book, "The Art of Electronics" by Horowitz and Hill, but I haven't read it. Maybe you could tell me if there's something in it that could help me.

Max

Sorry, you're right - I'm on crack. I didn't realize you needed an xtal to provide the actual carrier frequency, I thought you were using a cookbook/appnote circuit around one of the usual suspects for IR Tx. Normally the carrier is generated by a [masked] microcontroller which is clocked by something rather faster - as you observed :)

A crystal may not at all be necessary. The receiver contains a band pass filter that is not crystal based, and con pass a band of frequencies that is nominally centered around the specified frequency. For a single unit (not production) you can make a clock with an LMC555 timer, and adjust it to approximately the correct frequency by experiment. Find the highest frequency that works, the lowest that works, and set it to about the middle of that range.

Usually in approximately the AM radio IF (~455kHz) frequency range, IIRC. That's used for the clock of a microcontroller etc.

Best regards, Spehro Pefhany

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The web page explicitly says "The good news is that they still carry other frequency models. For example, there is the 38.0 kHz model (Jameco Part #131908) and the 37.9 kHz model (Jameco Part #139889). You can use either IR module and buy a matching crystal (Digikey carries them). The schematic is identical."

so there's nothing magic about 38 KHz. If you can find parts for any other frequency, you can use them instead. I have a vague recollection that something in the neighborhood of 42-44 KHz is more commonly used in commercial TV stuff.

Norm

Not the ones I've taken apart. Maybe it's changed with more recent ones, but the ones I've seen use a higher frequency ceramic resonator, around 450KHz is one that comes to mind.

I'm not sure why something would be using a 38KHz crystal. One reason you see more crystals in consumer electronics than thirty years ago is because once things went digital, it was easy to toss an extra divider into an IC, so cheap crystals could be used, no matter what the frequency that was needed. ANd the lower the frequency, the bigger and more expensive the crystal.

Michael

Then get a crystal oscillator, or a crystal and build an oscillator, and then add a divider to get it down to where the circuit needs it. So you pick a cheap available crystal, making sure it divides down evenly to the frequency you need (or maybe not, depending on how precise the frequency in your application must be), and making sure you can do it with the amount of division available in a cheap and common divider.

Michael

First of all your link does not work (try

\\tutorials/lrir/mc145026.htm ) and second they use a xtal of 32.768 kHz which is not rare at all.

-- DF

Yeah...too bad you can't get any of those in Germany without paying huge shipping fees and probably waiting weeks for it to arrive...

It says 32.768kHz actually.

A standard 'watch crytal'.

£0.44 from Farnell.

Graham

"Pooh Bear" schreef in bericht news: snipped-for-privacy@hotmail.com...

The website also says:

****** Updated Note (02/27/99): The 32.7 kHz IR module was originally carried by Jameco (part #106382), but was sadly discontinued.

The good news is that they still carry other frequency models. For example, there is the 38.0 kHz model (Jameco Part #131908) and the 37.9 kHz model (Jameco Part #139889). You can use either IR module and buy a matching crystal (Digikey carries them). The schematic is identical.

******

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Thanks, Frank.
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use a 38kHz resonator instead :)

Jaycar lists 38kHz crystals in their catalogue (jaycar.com.au) and they don't have an exhaustive range by any means. There's bound to be a supplier closer to you that has them. start with "electronic components" (or equivalent) in the yellow pages.

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Bye.
   Jasen

Hi Flashbiter.

You really need to at least have a clue of how to find out how to solve the problem,

An excellent first move.

Aha, I think you can spot the problem here :-)

It is a good book that will guide you into the subject but it has no circuits for what you wish to do.

Carriers vary from 32 to 39 kHz.

36 kHz is a good frequency in the middle of this range. Dividing a cheap TV colour carrier crystal should give adequate carriers 14318181 Hz / 400 = 3579545 Hz / 100 = 35.79545 kHz

You said you were *building* one. So what's wrong with using a

32.768kHz crystal ?

Graham

If the OP is using one of those integrated infrared receivers, he should note that they have filters in them. I'm thinking of the TSOP11xx parts. For example, if he has a TSOP1138 it'll attenuate much of the signal at

32kHz. delta f(3dB) = f0/7, so it'll filter out half the power at 32.758kHz.

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