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RE: [beam] Transistor Switch design problem

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  • Ian Crowther
    Hi everyone, I have a request for the secret masters. I m trying to build what basically amounts to an IR based proximity detector. IR LEDs shining outwards, a
    Message 1 of 12 , May 1, 2007
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      Hi everyone,
      I have a request for the secret masters.

      I'm trying to build what basically amounts to an
      IR based proximity detector. IR LEDs shining outwards,
      a photodiode to detect the reflection and at a certain
      brightness threshold trigger a motor.

      Input stage is a voltage divider using a reverse biased
      photodiode and a preset to adjust the sensitivity. This
      drives a 2 stage amplifier using 2n2222s

      So far I'm having very little luck getting the thing to
      work as desired. The main problem is the Photodiode's
      response is a nice smooth line which does not
      drive the transistors to saturation meaning that they get
      hot and don't provide enough oomph to start the motor.
      (If I start it by hand it turns just fine)

      Could someone who knows show me a diagram of a transistor
      switch with some kind of positive feedback or cleverness
      to give it a nice hard turn on ?

      I thankyou.
      ;;==============================================
      Ian
      If you can't make someone happy
      Make them Chocolate Fudge Cake.

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    • jdstufu
      can you post the schematics on the files or photo section and post a message after you ve done it :)
      Message 2 of 12 , May 1, 2007
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        can you post the schematics on the files or photo section and post a
        message after you've done it :)
      • Joseph Charles
        Can you post a schematic of what you have so far, Ian. I imagine you want to trigger the motor and have it latch on for a certain amount of time. Is this
        Message 3 of 12 , May 2, 2007
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          Can you post a schematic of what you have so far, Ian.

          I imagine you want to trigger the motor and have it latch on for a
          certain amount of time. Is this right?

          (I am not a secret master, but I'm willing to have a crack at it!)

          Jo
        • Joseph Charles
          Ian, you may be interested in this circuit from Wilf: http://tech.groups.yahoo.com/group/beam/files/wilf_nv/IRSYNCv3a.gif There is a discussion of the circuit
          Message 4 of 12 , May 2, 2007
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            Ian, you may be interested in this circuit from Wilf:

            http://tech.groups.yahoo.com/group/beam/files/wilf_nv/IRSYNCv3a.gif

            There is a discussion of the circuit in and around this post:

            http://tech.groups.yahoo.com/group/beam/message/50970

            Jo

            --- In beam@yahoogroups.com, "Ian Crowther" <ian.crowther@...> wrote:

            > I'm trying to build what basically amounts to an
            > IR based proximity detector. IR LEDs shining outwards,
            > a photodiode to detect the reflection and at a certain
            > brightness threshold trigger a motor.
          • Joseph Charles
            I have no idea just what Ian wants cos he seems to have gone walkabout. But I ve had a brief play with some transistors and have cobbled together this:
            Message 5 of 12 , May 5, 2007
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              I have no idea just what Ian wants 'cos he seems to have gone walkabout.

              But I've had a brief play with some transistors and have cobbled
              together this:

              http://tech.groups.yahoo.com/group/beam/files/Jo%20C/DiffAmpIRlatch.GIF

              It's only useful where the ambient light conditions are known and
              stable, so no use on a travelling 'bot which would need some immunity
              from ambient light conditions.

              Not the bet circuit in the world, but may give some ideas for further
              play.

              Cheers,

              Jo


              --- In beam@yahoogroups.com, "Joseph Charles" <jodicalhon@...> wrote:
              >
              > Can you post a schematic of what you have so far, Ian.
              >
              > I imagine you want to trigger the motor and have it latch on for a
              > certain amount of time. Is this right?


              --- In beam@yahoogroups.com, "Ian Crowther" <ian.crowther@...> wrote:

              > I'm trying to build what basically amounts to an
              > IR based proximity detector. IR LEDs shining outwards,
              > a photodiode to detect the reflection and at a certain
              > brightness threshold trigger a motor.
              >
              > Input stage is a voltage divider using a reverse biased
              > photodiode and a preset to adjust the sensitivity. This
              > drives a 2 stage amplifier using 2n2222s
              >
              > So far I'm having very little luck getting the thing to
              > work as desired. The main problem is the Photodiode's
              > response is a nice smooth line which does not
              > drive the transistors to saturation meaning that they get
              > hot and don't provide enough oomph to start the motor.
              > (If I start it by hand it turns just fine)
              >
              > Could someone who knows show me a diagram of a transistor
              > switch with some kind of positive feedback or cleverness
              > to give it a nice hard turn on ?
            • dukeeuphoria
              ... My apologies, the machine at this end melted down. walkabout would have been more fun, specially if it had Jenny Agutter in... The application is a fixed
              Message 6 of 12 , May 8, 2007
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                > I have no idea just what Ian wants 'cos he seems to have gone walkabout.
                My apologies, the machine at this end melted down.
                walkabout would have been more fun, 'specially if it had Jenny Agutter
                in...

                The application is a fixed installation which essentially has to run a
                motor when anyone waves a hand "too close" to it. Relatively stable
                lighting conditions, indoor, artificial light. But a fair endurance
                required, ie the circuit has to survive for at least a week without
                melting down, catching fire or becoming unreliable.
                Alas I must have been abusing the poor transistors somehow as I smoked
                a few of them whilst fiddling.

                > But I've had a brief play with some transistors and have cobbled
                > together this:
                > http://tech.groups.yahoo.com/group/beam/files/Jo%20C/DiffAmpIRlatch.GIF
                Many thanks, that's very helpful!

                > Not the bet circuit in the world, but may give some ideas for
                further play.

                Indeed it does, the feedback capacitor gives me a clue that I was lacking

                > > Can you post a schematic of what you have so far, Ian.

                http://tech.groups.yahoo.com/group/beam/files/PhotoDiode.gif
                mostly works but turns on very slowly.

                > > I imagine you want to trigger the motor and have it latch on for a
                > > certain amount of time. Is this right?

                Latching the motor is desirable but not essential,

                ;;=================
                Ian
              • Joseph Charles
                Ahh, g day Ian, nice to see you back. As regards your circuit, you don t need the 10k in parallel with the motor. Have a bit of a play, but I think you should
                Message 7 of 12 , May 8, 2007
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                  Ahh, g'day Ian, nice to see you back.

                  As regards your circuit, you don't need the 10k in parallel with the
                  motor.

                  Have a bit of a play, but I think you should have base resistors on
                  all transistors. The motor PNP's could be around 1k (but experiment).

                  Capacitor from the NPN's collector back to the midpoint of the PD/1M
                  pot voltage divider: If you don't have a small base resistor on the
                  first PNP then the voltage at this point can't go any lower than Vcc -
                  0.7V, which is the voltage across the base/emitter junction of the
                  PNP. You want the capacitively coupled low from the NPN's collector to
                  pull the voltage divider midpoint low(er). This will then time-out as
                  the capacitor is charged from Vcc via the 1M pot.

                  Let us know how you go. If I get some time I'll have a fiddle myself.

                  Cheers,

                  Jo


                  Ian wrote:
                  > http://tech.groups.yahoo.com/group/beam/files/PhotoDiode.gif
                  > mostly works but turns on very slowly.
                • Joseph Charles
                  Hi Ian, While waiting for some glue to dry on the K9 robot I m making, I had bit of a fiddle with your circuit and tried two variations which may, or may not,
                  Message 8 of 12 , May 9, 2007
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                    Hi Ian,

                    While waiting for some glue to dry on the K9 robot I'm making, I had
                    bit of a fiddle with your circuit and tried two variations which may,
                    or may not, be OK for your app.

                    http://tech.groups.yahoo.com/group/beam/files/Jo%20C/IRlatches.GIF

                    See what you think.

                    Cheers,

                    Jo


                    --- In beam@yahoogroups.com, "Joseph Charles" <jodicalhon@...> wrote:


                    > As regards your circuit, you don't need the 10k in parallel with the
                    > motor.
                    >
                    > Have a bit of a play, but I think you should have base resistors on
                    > all transistors. The motor PNP's could be around 1k (but experiment).
                  • Joseph Charles
                    Of course, you could always go for a 38kHz IR detector and a modulated IR source. Might be easier and more reliable. Jo
                    Message 9 of 12 , May 9, 2007
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                      Of course, you could always go for a 38kHz IR detector and a modulated
                      IR source. Might be easier and more reliable.

                      Jo



                      --- In beam@yahoogroups.com, "Joseph Charles" <jodicalhon@...> wrote:
                      >
                      > Hi Ian,
                      >
                      > While waiting for some glue to dry on the K9 robot I'm making, I had
                      > bit of a fiddle with your circuit and tried two variations which may,
                      > or may not, be OK for your app.
                      >
                      > http://tech.groups.yahoo.com/group/beam/files/Jo%20C/IRlatches.GIF
                      >
                      > See what you think.
                      >
                      > Cheers,
                      >
                      > Jo
                      >
                      >
                      > --- In beam@yahoogroups.com, "Joseph Charles" <jodicalhon@> wrote:
                      >
                      >
                      > > As regards your circuit, you don't need the 10k in parallel with the
                      > > motor.
                      > >
                      > > Have a bit of a play, but I think you should have base resistors on
                      > > all transistors. The motor PNP's could be around 1k (but experiment).
                      >
                    • Ian Crowther
                      Hiya, Many thanks for devoting some time to this, The second circuit you posted is similar to one I had a while back. I must dig out the schematic and find out
                      Message 10 of 12 , May 9, 2007
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                        Hiya, Many thanks for devoting some time to this,
                        The second circuit you posted is similar to one I had
                        a while back. I must dig out the schematic and find out
                        why mine wasn't working.
                        It would trigger on, but then remain latched and never
                        turn off, that was the point I decided I'd missed out
                        some entirely fundamental idea about how these things
                        work and squeaked for help.

                        With a little luck I'll get a chance to get to the bench
                        sometime tomorrow and have another fiddle.

                        Alas finding someone that will sell me a modulated receiver
                        is proving slightly problematic. Many places claim to have
                        them available, but when I call they seem to be unaccountably
                        out of stock.

                        Hey ho...

                        Thanks once again, this is really very helpful.
                        ;;==========================
                        Ian
                        Back to the wall,
                        Nose to the grindstone
                        Shoulder to the wheel,
                        Head in the clouds...



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                      • Joseph Charles
                        No worries, Ian, this is how I enjoy myself. (Of course, it would help if I knew what I was doing...) With the second circuit, I have reduced R1 to zero ohms
                        Message 11 of 12 , May 10, 2007
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                          No worries, Ian, this is how I enjoy myself. (Of course, it would help
                          if I knew what I was doing...)

                          With the second circuit, I have reduced R1 to zero ohms and it snaps
                          in to action no problem.

                          I originally had R1 as 10k (or less) to add some hysteresis to the
                          input, because I thought it might oscillate on and off if the IR level
                          was just at the trigger point. It added the danger that the hysteresis
                          might be too large, and you'd never turn the thing off, hence my
                          advice to keep the value of R1 low (<10k).

                          It seems I didn't have to worry. R1=zero works fine, and no hysteresis
                          induced problems. No latching for a time period, though. Next time, eh.

                          Best of luck,

                          Jo

                          --- In beam@yahoogroups.com, "Ian Crowther" <euphoria@...> wrote:
                          >
                          >
                          > Hiya, Many thanks for devoting some time to this,
                          > The second circuit you posted is similar to one I had
                          > a while back. I must dig out the schematic and find out
                          > why mine wasn't working.
                          > <snip>
                          > Ian
                          > Back to the wall,
                          > Nose to the grindstone
                          > Shoulder to the wheel,
                          > Head in the clouds...
                          >
                          >
                          >
                          >
                          __________________________________________________________________________________________________________________________________________
                          > Information contained in this e-mail is intended for the use of the
                          addressee only, and is confidential and may be the subject of Legal
                          Professional Privilege. Any dissemination, distribution, copying or
                          use of this communication without prior permission of the addressee is
                          strictly prohibited.The views of the author may not necessarily
                          constitute the views of Kuju Entertainment Ltd. Nothing in this email
                          shall bind Kuju Entertainment Ltd in any contract or obligation.
                          >
                          > The contents of an attachment to this e-mail may contain software
                          viruses which could damage your own computer system. While Kuju
                          Entertainment has taken every reasonable precaution to minimise this
                          risk, we cannot accept liability for any damage which you sustain as a
                          result of software viruses. You should carry out your own virus checks
                          before opening the attachment.
                          >
                          > Registered Office : 10 Woodside Park, Catteshall Lane, Godalming,
                          Surrey, UK, GU7 1LG. Company Number : 3481384.Company Registered in
                          England.
                          >
                          __________________________________________________________________________________________________________________________________________
                          > This email has been scanned by the MessageLabs Email Security System.
                          > For more information please visit http://www.messagelabs.com/email
                          >
                          _________________________________________________________________________________________________________________________________________
                          >
                        • Joseph Charles
                          If the circuit does latch on, never to turn off, try backing off the sensitivity. Have a good look at Wilf s IRSynchv3a circuit I linked to earlier. I did some
                          Message 12 of 12 , May 10, 2007
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                            If the circuit does latch on, never to turn off, try backing off the
                            sensitivity.

                            Have a good look at Wilf's IRSynchv3a circuit I linked to earlier. I
                            did some testing of this circuit and it proved itself very sensitive,
                            and pretty much immune to ambient light conditions.

                            The parts count is up, but so is the effectiveness.

                            If you follow the discussion links at the bottom of the post that I
                            linked to, you might find them of some interest.

                            I can't find the original post, but the general idea is that the
                            receiver only turns on for the brief instant that the transmitter fires.

                            See ya,

                            Jo (returning to K9...)


                            --- In beam@yahoogroups.com, "Joseph Charles" <jodicalhon@...> wrote:

                            > With the second circuit, I have reduced R1 to zero ohms and it snaps
                            > in to action no problem.
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