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quick question

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  • xavier1134
    honestly, I m not too familiar with the mechanism with which reverse-biased infrared emitters/phototransistors work, particularly in reference to photopoppers.
    Message 1 of 6 , Oct 1, 2007
      honestly, I'm not too familiar with the mechanism with which
      reverse-biased infrared emitters/phototransistors work, particularly
      in reference to photopoppers. I've got a bunch of LDR's (1M dark, 300k
      light) - can I use them instead, or do I have to go get some IR LED's?

      Thanks,
      David
    • Joseph Charles
      The reverse-biased components are generally photodiodes. You can usually replace them with LDR s, however, this can depend on the circuit you re modifying. Do
      Message 2 of 6 , Oct 2, 2007
        The reverse-biased components are generally photodiodes. You can
        usually replace them with LDR's, however, this can depend on the
        circuit you're modifying.

        Do you have a particular circuit in mind?

        Jo

        --- In beam@yahoogroups.com, "xavier1134" <david.lesser@...> wrote:
        >
        > honestly, I'm not too familiar with the mechanism with which
        > reverse-biased infrared emitters/phototransistors work, particularly
        > in reference to photopoppers. I've got a bunch of LDR's (1M dark, 300k
        > light) - can I use them instead, or do I have to go get some IR LED's?
        >
        > Thanks,
        > David
        >
      • xavier1134
        I was thinking of the basic 1381-based photopopper, such as the one on solarbotics.net. David
        Message 3 of 6 , Oct 2, 2007
          I was thinking of the basic 1381-based photopopper, such as the one on
          solarbotics.net.

          David

          --- In beam@yahoogroups.com, "Joseph Charles" <jodicalhon@...> wrote:
          >
          > The reverse-biased components are generally photodiodes. You can
          > usually replace them with LDR's, however, this can depend on the
          > circuit you're modifying.
          >
          > Do you have a particular circuit in mind?
          >
          > Jo
          >
          > --- In beam@yahoogroups.com, "xavier1134" <david.lesser@> wrote:
          > >
          > > honestly, I'm not too familiar with the mechanism with which
          > > reverse-biased infrared emitters/phototransistors work, particularly
          > > in reference to photopoppers. I've got a bunch of LDR's (1M dark, 300k
          > > light) - can I use them instead, or do I have to go get some IR LED's?
          > >
          > > Thanks,
          > > David
          > >
          >
        • Joseph Charles
          I m happy to be corrected on this, but I don t think a direct replacement can be made. The original circuit relies, I think, on the photovoltaic output of the
          Message 4 of 6 , Oct 3, 2007
            I'm happy to be corrected on this, but I don't think a direct
            replacement can be made.

            The original circuit relies, I think, on the photovoltaic output of
            the photodiodes/LED's. When photodiodes, or any LED's, are exposed to
            light they generate a little voltage of their own, like a small solar
            cell. This voltage is around 0.5V, and varies a bit with the light
            intensity.

            In the circuit on this page,
            http://www.solarbotics.net/library/circuits/bot_popper_1381.html
            the photodiode in the brighter light generates a slightly higher
            voltage than the one in shadow, and this is added to the voltage from
            the main supply capacitor, so that side pops first.

            LDR's don't generate a voltage, and I think they would just act as
            pullups on the sensing pins of the 1381's. I doubt there would be much
            difference between the voltage on the two sides, no matter what the
            light differential.

            However, I think you can probably use them, with a 10k pot, in a
            voltage divider configuration.

            With reference to the above circuit: take out the photodiodes. Change
            the 100k pot for a 10k pot. Connect the ends of the 10k pot to the
            sensing pins of the 1381's. Put an LDR between each 1381 sensing pin
            and gnd.

            The drawback I see with this is that the trigger voltage of the popper
            will vary with the light intensity. If your LDR's drop to a low
            resistance in bright light then the 1381 will be waiting in vain for a
            trigger voltage, as the bulk of the main capacitor's voltage will be
            dropped across the pot. Maybe a 2k trimmer pot would be better.

            Or replace the photodiodes with green LED's. These seem to generate a
            goodly voltage under light and are far more common than IR photodiodes.

            Just my tuppence worth.

            Cheers,

            Jo



            --- In beam@yahoogroups.com, "xavier1134" <david.lesser@...> wrote:
            >
            > I was thinking of the basic 1381-based photopopper, such as the one on
            > solarbotics.net.
            >
            > David
            >
            > --- In beam@yahoogroups.com, "Joseph Charles" <jodicalhon@> wrote:
            > >
            > > The reverse-biased components are generally photodiodes. You can
            > > usually replace them with LDR's, however, this can depend on the
            > > circuit you're modifying.
            > >
            > > Do you have a particular circuit in mind?
            > >
            > > Jo
            > >
            > > --- In beam@yahoogroups.com, "xavier1134" <david.lesser@> wrote:
            > > >
            > > > honestly, I'm not too familiar with the mechanism with which
            > > > reverse-biased infrared emitters/phototransistors work, particularly
            > > > in reference to photopoppers. I've got a bunch of LDR's (1M
            dark, 300k
            > > > light) - can I use them instead, or do I have to go get some IR
            LED's?
            > > >
            > > > Thanks,
            > > > David
            > > >
            > >
            >
          • jabmechtech
            HI, I am finishing up a photovore that runs off of 2, 3 Vdc rechargeable button cell.Lithium Batteries. I want to place a 9v solar cell on top to charge the
            Message 5 of 6 , Aug 2, 2011
              HI,
              I am finishing up a photovore that runs off of 2, 3 Vdc rechargeable button cell.Lithium Batteries. I want to place a 9v solar cell on top to charge the battery when the switch is in the off position. The robot is built except for the solar cell on top at this point.
              I know I need to place a Diode on the + line from the battery to the solar cell. My question is.
              Which way does it go? what gets the negative end battery or solar cell?
              Thanks.
              Jabmechtech
              Build your dreams.
            • arno_brosi
              Hi Jab,I believe the negative end is closest to the battery(you want to prevent the charge going back to the solar cell) best wishes,Arno
              Message 6 of 6 , Aug 3, 2011
                Hi Jab,I believe the negative end is closest to the battery(you want to prevent the charge going back to the solar cell)

                best wishes,Arno

                --- In beam@yahoogroups.com, "jabmechtech" <jabmechtech@...> wrote:
                >
                > HI,
                > I am finishing up a photovore that runs off of 2, 3 Vdc rechargeable button cell.Lithium Batteries. I want to place a 9v solar cell on top to charge the battery when the switch is in the off position. The robot is built except for the solar cell on top at this point.
                > I know I need to place a Diode on the + line from the battery to the solar cell. My question is.
                > Which way does it go? what gets the negative end battery or solar cell?
                > Thanks.
                > Jabmechtech
                > Build your dreams.
                >
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