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Re: [beam] Re: beginning BEAM questions

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  • Wilf Rigter
    Here are two circuits that provide the double modulated IR beam. I used 40kHz but this is a nominal value that can be adjusted to suit. The 40kHzHerbie1
    Message 1 of 7 , Sep 30, 2005
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      Here are two circuits that provide the double modulated IR beam. I used 40kHz but this is a nominal value that can be adjusted to suit. The 40kHzHerbie1 circuit uses two 555 (or a single 556) timers for excelent stability. The 40kHzHerbie2 circuit uses two 74HC14 Schmitt triggers, is simpler but may drift more. The component values of the 40kHz oscillator will require fine tuning for the right frequency.
      This is a general purpose solution that may be used in other designs.
       
      wilf
       
       
       
      ----- Original Message -----
      From: wilf_nv
      Sent: Friday, September 30, 2005 3:02 PM
      Subject: [beam] Re: beginning BEAM questions


      I just love questions which trigger an idea for an interesting
      solution as I write the reply.

      38kHz IR receivers have digital (on/off) outputs signals and cannot
      be interfaced directly with the LM386 inputs. The LM386 "expects" two
      small analog input signals the difference of which is amplified and
      raises or lowers the analog output voltage  connected to the midpoint
      of the two series connected motors. When the inputs signals are
      balanced the LM386 output voltage is +V/2.

      So how do we convert the 38KHz RX output from digital to analog?

      To convert the digital output of these IR receivers to an analog
      function that can interface with the LM386, the 38kHz carrier
      frequency must also be frequency or amplitude modulated at a lower
      frequency (ie 100Hz) with a triangle waveform.  Since the receivers
      trigger and reset at some minimum light level at the center of the
      carrier frequency, the 0-100ma ramping LED current which controls the
      IR LED light level will cross this threshold at some light level.
      Using a ramping amplitude modulation  causes the receiver with the
      higher light level to trigger earlier and reset later than the
      receiver exposed to the lower light level. When the light exposure is
      the same on both receivers, they should trigger and reset at the same
      time.

      Similarly, +/- 1kHz frequency modulation of the 38kHz carrier will
      have the same effect as the receiver sensitivity is a combination of
      both amplitude and LED frequency variation with respect to the center
      frequency.

      FM is more efficient in terms of controlling LED current but AM may
      provide better sensitivity and linearity of the receiver response. 
       
      The resulting IR receiver output waveforms will be 100Hz Pulse Width
      Modulated rectangular waveforms which can be filtered to convert to
      analog and then connected to the two LM386 inputs to generate the
      LM386 analog output signal based on the difference in analog signal
      at the inputs.     

      This design should be quite straight forward and I will be happy to
      post a complete circuit of this 38kHz Herbie a little later tonite.

      One more comment:  Unlike the differential 38kHz receiver for Herbie
      applications as described, an absolute distance measurement would be
      difficult as these highly integrated 38kHz IR receivers have
      automatic gain control (AGC) to compensate for changes in light level.

      wilf

      --- In beam@yahoogroups.com, "mountainieer2000"
      <mountainieer2000@y...> wrote:
      > hi,
      >
      > I am trying to build a little BEAM robot that will home on a special
      > light source by using a LM386 and two 38k Hz IR Reciever modules
      from
      > Radio Shack(part number 276-640). How would I wire them and would
      they
      > work to home in on a 38k Hz source from a 555 timer?
      >
      >
      > On a seperate tangent, I am trying to use a little surplus wireless
      > phone battery (3.6v) to power the above mentioned robot. It came
      with
      > wires but they apparently lead nowhere(they had no voltage across
      > them). The battery has two metal plates on it, one on each side, who
      > happen to have 3.6v accross them so I tried soldering new leads onto
      > them. The solder did not flow on like it is suppossed to. I even
      tried
      > "painting" on the solder to form a cold solder. That also didn't
      work.
      > The solder does not adhere/stay on. Any suggestions on how to attach
      > the leads, either with a different soldering technique or different
      > mechanism(zip ties/tape?)?
      >
      > Thanks in advance, mountainieer2000


    • Wilf Rigter
      oops! Oh well, Here are two circuits that provide the double modulated IR beam. I used 40kHz but this is a nominal value that can be adjusted to suit. The
      Message 2 of 7 , Sep 30, 2005
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        oops!
         
        Oh well,
         
        Here are two circuits that provide the double modulated IR beam. I used 40kHz but this is a nominal value that can be adjusted to suit. The 40kHzHerbie1 circuit uses two 555 (or a single 556) timers for excelent stability. The 40kHzHerbie2 circuit uses two 74HC14 Schmitt triggers, is simpler but may drift more. The component values of the 40kHz oscillator will require fine tuning for the right frequency.This is a general purpose solution that may be used in other designs
         
        wilf
      • Joseph Charles
        Hi Wilf, what an interesting idea. I can see how the circuits are amplitude modulating the IR beam (via the ramping triangle wave), but how are they frequency
        Message 3 of 7 , Oct 3, 2005
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          Hi Wilf, what an interesting idea. I can see how the
          circuits are amplitude modulating the IR beam (via the
          ramping triangle wave), but how are they frequency
          modulating it?

          I know I'm a pedant (sorry!), but should the cap value
          of the lower 555 be more like 0.001uF, not 1uF? What
          would you suggest for the value of the cap in the
          receiver circuit?

          I can see I'll be up one night this week measuring
          things again! :)

          Jo


          --- Wilf Rigter <wrigter@...> wrote:

          > Here are two circuits that provide the double
          > modulated IR beam. I used 40kHz but this is a
          > nominal value that can be adjusted to suit. The
          > 40kHzHerbie1 circuit uses two 555 (or a single 556)
          > timers for excelent stability. The 40kHzHerbie2
          > circuit uses two 74HC14 Schmitt triggers, is simpler
          > but may drift more. The component values of the
          > 40kHz oscillator will require fine tuning for the
          > right frequency.
          > This is a general purpose solution that may be used
          > in other designs.
          >
          > wilf




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        • Wilf Rigter
          Hi Jo, I should have pointed out that this idea uses either AM modulation OR FM modulation but not both. Cut, paste and MODIFY darn it! You are absolutely
          Message 4 of 7 , Oct 3, 2005
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            Hi Jo,
             
            I should have pointed out that this idea uses either AM modulation OR FM modulation but not both.
            Cut, paste and MODIFY darn it! You are absolutely right about the cap of the lower 555:  it should be 0.001uF.   The filter cap on the output should be about 0.33 -1uF. The 100K pull up resistors are probably not required. Good luck with testing it.
             
            wilf
             
                
            ----- Original Message -----
            Sent: Monday, October 03, 2005 5:51 AM
            Subject: [beam] Re: beginning BEAM questions

            Hi Wilf, what an interesting idea. I can see how the
            circuits are amplitude modulating the IR beam (via the
            ramping triangle wave), but how are they frequency
            modulating it?

            I know I'm a pedant (sorry!), but should the cap value
            of the lower 555 be more like 0.001uF, not 1uF? What
            would you suggest for the value of the cap in the
            receiver circuit?

            I can see I'll be up one night this week measuring
            things again! :)

            Jo


            --- Wilf Rigter <wrigter@...> wrote:

            > Here are two circuits that provide the double
            > modulated IR beam. I used 40kHz but this is a
            > nominal value that can be adjusted to suit. The
            > 40kHzHerbie1 circuit uses two 555 (or a single 556)
            > timers for excelent stability. The 40kHzHerbie2
            > circuit uses two 74HC14 Schmitt triggers, is simpler
            > but may drift more. The component values of the
            > 40kHz oscillator will require fine tuning for the
            > right frequency.
            > This is a general purpose solution that may be used
            > in other designs.
            >
            > wilf



                       
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