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Date: Sat, 28 Dec 2002 13:08:46 +0100
From: Rene Tschaggelar
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Subject: Re: IR detection problem
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> Hi John,
> I am not sure that I can generate how high of the frequency of IR source at
> this moment, may be only 1k to 5kHz. As I never try analog/RF design before,
> I do not know how to use/design bankpass filter and detect amplitude with
> MCU. Any external components need? Can you suggest a website or schematics
> for me?
> If the frequency of my source is 1k-5kHz, is this method still OK?
>John Popelish wrote :
>>I do not understand what modulation method you have tried. One
>>effective method is to turn your IR source on and off at a frequency
>>that is much higher than your bit rate. Then pass the detector signal
>>through a band pass filter centered on the modulation frequency, and
>>detect the envelope of the signal from the filter, just the way an
>>amplitude modulation detector works in a radio.
when the frequency is 1kHz to 5kHz you can apply synchroneous
detection. At the photodiode have an AC amplifier that has a passband
around the frequency of interest. This is done with one or more
external OpAmps and a few R & C. Then also invert this signal.
Use an Analog switch to select either the straight signal or
the inverted signal and feed that onto an RC of say 100Hz.
The Analog switch is controlled by the transmitter.
This way, the noise is removed. The achievable bandwidth is below
the mentioned Lowpass of 100Hz.
This signal is somehow fed to the micro, perhaps after some
I'd recommend some external hardware that allows a higher frequency
than the 1-5kHz.
Ing.Buero R.Tschaggelar - http://www.ibrtses.com
& commercial newsgroups - http://www.talkto.net
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