Infrared RC oscillator
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Posted by Michael on January 11, 2006, 3:05 pm
Please log in for more thread options 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). Thanks. | |||||||||||||||||||||||||
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Posted by Charles Schuler on January 11, 2006, 3:14 pm
Please log in for more thread options 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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Posted by John Fields on January 11, 2006, 5:59 pm
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wrote: >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). --- Yes. Completely neglecting the power supply, to get into the same ball park with a ceramic resonator would require your circuit's resonant parts to have tolerances on the order of +/- 0.05%. There's no way you can even get close, for the money. -- John Fields Professional Circuit Designer | |||||||||||||||||||||||||
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Posted by Frank Bemelman on January 11, 2006, 9:16 pm
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> So many of the xmtr circuits I've seen for infrared remote control use a
parts
> crystal or ceramic resonator in a cmos oscillator. > > Is there any reason why an R/C network oscillator using low tolerance > wouldn't be accurate enough at such a low frequency?
> (38 or 40 khz). 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. (remove 'q' and '.invalid' when replying by email) | |||||||||||||||||||||||||
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Posted by Pooh Bear on January 11, 2006, 9:17 pm
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Michael wrote: > 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). 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. Graham | |||||||||||||||||||||||||
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> 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).