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"active band pass fileter design help"

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by KaJuan, Aug 10, 2004.

  1. KaJuan

    KaJuan New Member

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    I am making a active sensor which utilizes an IR LED and a phototransistor. The IR LED would trasmit IR Light and the phototransistor recives the IR Light only if there is a n object near by. Every thing works well except that the phototransistor also detects evironement light. So I decide to modulate the IR signal to 100KH while the phototransistor is to be connectect to a bandpass filter that would allow the 100KH signal to pass. THe problem is that I dont know how to design an active band pass filter that could allow 100KH signal to pass. Could any body pls help me?

    Thank you in advance and more power
     
  2. evandude

    evandude New Member

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    it would be easier to just use a tone detector IC. this is the typical method for most of the modulated IR receivers I have seen, as well as ultrasonics. you will then get a nice clean digital output from it.
    you may also wish to use 40kHz as your modulation frequency, as that is by far the most common frequency to use (38kHz is also common)
    and it is what is used in many TV remote controls (which allows you to test your circuit easily using a known-working TV remote)
     
  3. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    It's far easier (and probably more reliable) to just use an IR receiver IC, you can use a simple 555 timer (or anything else you wanted) to modulate the IR LED at 38-40KHz. The receiver would be just one three pin IC, and the transmitter very few parts as well.

    My website http://www.lpilsley.co.uk/cybot/radar.htm includes a design using a PIC 12C508 with two IR LED's to detect obstacles to left or right.
     
  4. dave

    Dave New Member

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  5. KaJuan

    KaJuan New Member

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    For Sir Evandude... Sir could you sudgest a couple of tone reciever IC's? The problem here in our place is the availability of those IC's I hope I could find one of those IC's that you will mention...

    Thank you once again and more power
     
  6. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    I think the NE567 is a common one!.
     
  7. evandude

    evandude New Member

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    yes, the NE567 is the one that I have used in the past.
     
  8. KaJuan

    KaJuan New Member

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    other tone decoder ICs

    are there other tone decoder IC other than the LM567?

    thank you for replying to my message.

    Thank you once again and more power
     
  9. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Re: other tone decoder ICs

    I believe you can configure the CMOS 4046 PLL chip as a tone decoder, a tone decoder is just a particular use of a PLL - but the 567 is specifically designed for the purpose, and is very simple to use.
     
  10. KaJuan

    KaJuan New Member

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    PLL

    How do you configure a PLL to become a tone decoder?
     
  11. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Re: PLL

    By checking to see if the PLL is locked, while the 4046 doesn't specifically provide a 'lock indicator' output you can easily provide one - it's a standard technique. But far easier to use the 567!.
     

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