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In lugnet.robotics.handyboard, FRED MARTIN <fm2852@chi.devry.edu> writes:
> Maybe somebody could help.
> I am try to use the IR output. the problem is that the HB is modulating the
> signal at 41kHz and I need to get it down to 38kHz.
> I have checked the resistor and capacitor used in generating the frequency.
>
> R =3D 3.81 K
> C =3D 0.0068uF
> f =3D 1/(3.81k)(.0068uF) =3D 38.5981kHz
>
> at least in theory.=20
>
> When I run the command poke(0x1000, 0x40); as Fred suggests in the test
> procedures I get about 43kHz at the output of U9-Pin 2(hex inverter)
> Which is high compared to the suggested output. (39k - 40k)Hz
> I am really trying to avoid replacing the res. and cap.
> I was wondering if anybody else had a problem with their IR output.
> If so could you let me know your experience. I am baffled as to why there
> is such a difference from theory to actual.
> I have been through the HB archives and cannot find a thing. So any help at
> all is welcomed and appreciated.
The obvious question is how you are measuring your capacitor and resistor
values?. Resistors (presumably metal film), are typically +/-1%, but
capacitors are unlikely to be 'better' than +/-5%, and may be significantly
worse than this (many 'normal' capacitor lines are +/-20%, whiole +/-10% is
typical. So any oscillator based on this type of component, could easily cover
your 'real' frequency. A frequqncy in the order of 43k, from an oscillator
designed to give 38.6k, sounds typical for such a component. This is why
filter designs end up using expensive 1% capacitors. If this is for infra red
comm's, then I wouldn't worry. The '38k' used is very nominal, with the IR
receiver on (say) the Mindstorms typically accepting frequencies from about
26k to over 50k. At the end of the day you are just going to have to change
your resistor, or 'accept' that you now understand teh effect of component
tolerances...
Best Wishes
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| Maybe somebody could help. I am try to use the IR output. the problem is that the HB is modulating the signal at 41kHz and I need to get it down to 38kHz. I have checked the resistor and capacitor used in generating the frequency. R = 3.81 K C = (...) (25 years ago, 12-Feb-00, to lugnet.robotics.handyboard)
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