Infrared RC oscillator

So many of the xmtr circuits I've seen for infrared remote control use a crystal or ceramic resonator in a cmos oscillator.

Is there any reason why an R/C network oscillator using low tolerance parts wouldn't be accurate enough at such a low frequency? (38 or 40 khz).


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Economics. It is easier to use a resonator and a frequency divider to get the required stability ... the only significant source of error is the resonator itself and they are quite stable and inexpensive. With RC control, one has several drift sources and inexpensive capacitors have temperature problems. Also, don't forget about trimming ... the resonator approach works every time with no adjustments.

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Charles Schuler

Yeah, I've used a ceramic resonator before with great results.

I took a 400khz and divided by 10 and the xmtr worked great.

I had these 38khz receiver modules in my parts drawer and been having some difficulty as I couldn't find anything in a ceramic resonator that was either 38khz or divide down to it. (?)

Looked everywhere....digi key, mouser, newark...nothing.

Plenty of 40 and 400 CR though.

So I wasted alot of time breadboarding a 4011 with a 38khz works but the start up time is ridiculous and a little change in Vcc changes the frequency so much.

I thought an R/C might be alright at only 38khz but I'll go back to the ceramic resonator and 40khz.

Why no 38 khz CR parts? There is a 420 and 455 khz that divided can get close.

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Yes.  Completely neglecting the power supply, to get into the same
ball park with a ceramic resonator would require your circuit\'s
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Reply to
John Fields

"Michael" schreef in bericht news:YdWdnQPDM5KZ-FjenZ2dnUVZ


With all the things that can and will go wrong, a ceramic resonator turns out to be the cheapest solution. That is reason enough.

Thanks, Frank.
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Reply to
Frank Bemelman

Your RC oscillator should be as accurate as the tolerance of the parts used. In other words probably fine for this application.

I'd use a wein bridge configuration with a fixed gain of say ~ 4-5 since a sine output isn't needed.


Reply to
Pooh Bear

Linear Technology has some cute RC oscillators. Use a resistor to set frequency. They are pretty accurate and stable for an RC oscillator. The LTC6906 draws under 20uA. $2.50 for the LTC6906 might be a bit steep if your dealing with large quantities. Digi-Key carries this line.

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Just because the frequency is low doesn't mean the accuracy required is any less. In practice it gets tricky getting RC repeatability better then about 5%, especially where supply voltage is likely to be variable, partly due to the high pulse currents driving the IR LED. A 5% frequency error will put the carrier far enough out of band for some IR sensors to reduce range noticeably. Resonators are cheap and stable and provide the best solution for this application - the proof of this is simply that it's what's almost universally used in an extremely price-sensitive market.

Reply to
Mike Harrison

less. In practice it

supply voltage is likely

Actually a circuit using a 555 timer will have pretty good immunity to voltage variations, OTOH the 555 may cost as much as a ceramic resonator, and the frequency is still dependent on high-tolerance and temperature-varying resistors and capacitors.


application - the proof of

price-sensitive market.

Reply to
Ben Bradley

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