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Re: [beam] phototaxis

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  • wilf rigter
    Hi Ryan, I just couldn t resist cooking up an example of a phototaxis following bot. The attached circuit has photobridge LDR1 mounted in front and LDR2 in the
    Message 1 of 22 , Apr 1 12:02 AM
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      Hi Ryan,
       
       I just couldn't resist cooking up an example of a phototaxis following bot.
       
      The attached circuit has photobridge LDR1 mounted in front and LDR2
       in the rear.  The delay cicruit is the special bicore I posted earlier
      which lends itself to this application. The bicore generates a long run
      delay and a short spin delay. Both delays are influenced by the
      resistance ratio of the LDRs which depends on the ratio of light
      front to back.  If LDR1 is brighter than LDR2, the delay is longer
      and vice versa. When the short delay is active Beamus spins for a
      short random time  (<1sec) before it times out and Beamus starts
      rolling straight forward in a random direction for the duration of the
      longer (1-10sec) run delay. The run delay times out quickly if the
      light gradient is stronger back to front and times out slowly if the
      light gradient is stronger front to back as determined by the ratio
      of the LDR rsistances . The two caps and the 1M /10M resistors
      can be changed to suit for different delays and sensitivity.
      With the photo gradient dependent delay time and random
      motion this bot will eventually converge on the brightest light even in
      a complex or random environment.
       
      wilf
       
       
      ----- Original Message -----
      From: Ryan W
      Sent: Monday, March 31, 2003 9:08 PM
      Subject: Re: [beam] phototaxis

      I was thinking of two photo sensors, one on the front,
      one on the back. compare the difference, if there is
      more light on the 'head' then longer run, more light
      on the 'tail' then shorter run.

      Ryan  

      --- wilf rigter <wrigter@...> wrote:
      > Hi Ryan,
      >
      > Perhaps random sampling is not the most efficient
      > way for phototaxis but the motion sure would look
      > organic. For chemotaxis, random sampling it is very
      > necesary as motion through the local gradient is
      > part of sampling. Also there  is no long range
      > gradient detection as there is with light. The
      > closest human experience would be like following
      > your nose, nudge, wink. After all, a given gradient
      > may be strong but you won't know if it is the
      > strongest unless you compare.
      >
      > Anyway the task is very simple,
      >
      > Random turn, reset delay, move forward,  delay time
      > out proportional to the light level. In other words
      > the delay to the next random turn is short in the
      > dark and long in the light. Anyone care to design a
      > Beamus Photo Taxis?
      >
      > wilf 
      >
      >    
      >   ----- Original Message -----
      >   From: wilsonryanj
      >   To: beam@yahoogroups.com
      >   Sent: Monday, March 31, 2003 7:31 PM
      >   Subject: [beam] phototaxis
      >
      >
      > I'm new to BEAMing, and to this group, but I have
      > always had an interest in electronics (There's the E)
      > and I have  B.S. in biology (there's the B)  I have
      > an idea for a photovore/photopopper, and I don't have
      > enough knowledge of electonics to implement it. 
       
      > Basicly it's similar to how bacteria move toward an
      > attractant, or chemotaxis.
      > They run for a period of time then abruptly change
      > to a new direction.  If they are moving up the gradient
      > to higher attractant concentrations, the length of the
      > run will increase, with less frequent direction changes.
      > If they are moving down the gradient, the length of the
      > run will be much shorter, and more frequent direction
      > changes.  This may not be the fastest or most direct
      > path to a light source, but I think it'd be interesting
      > to watch.   I have a few ideas I've been tossing around,
      > but I'm interested to  see what this group can come up with.
      >
      >   Thanks,
      >   Ryan
      >
       
      =====
      ICQ = 114482910

    • Ryan
      Thanks a lot! I don t have time to look too closely at it right now, but the behavior sounds like what I m looking for. Thanks again, Ryan
      Message 2 of 22 , Apr 1 10:33 AM
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        Thanks a lot! I don't have time to look too closely at it right now, but the
        behavior sounds like what I'm looking for.

        Thanks again,
        Ryan


        On Tuesday 01 April 2003 03:02 am, wilf rigter wrote:
        > Hi Ryan,
        >
        > I just couldn't resist cooking up an example of a phototaxis following
        > bot.
        >
        > The attached circuit has photobridge LDR1 mounted in front and LDR2
        > in the rear. The delay cicruit is the special bicore I posted earlier
        > which lends itself to this application. The bicore generates a long run
        > delay and a short spin delay. Both delays are influenced by the
        > resistance ratio of the LDRs which depends on the ratio of light
        > front to back. If LDR1 is brighter than LDR2, the delay is longer
        > and vice versa. When the short delay is active Beamus spins for a
        > short random time (<1sec) before it times out and Beamus starts
        > rolling straight forward in a random direction for the duration of the
        > longer (1-10sec) run delay. The run delay times out quickly if the
        > light gradient is stronger back to front and times out slowly if the
        > light gradient is stronger front to back as determined by the ratio
        > of the LDR rsistances . The two caps and the 1M /10M resistors
        > can be changed to suit for different delays and sensitivity.
        > With the photo gradient dependent delay time and random
        > motion this bot will eventually converge on the brightest light even in
        > a complex or random environment.
        >
      • GrantM
        Morning! Just did a quick test of Wilf s circuit, works exactly as described but the delay can be upwards of 15 seconds. Depending on the speed of your motors
        Message 3 of 22 , Apr 1 10:34 AM
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          Morning!

          Just did a quick test of Wilf's circuit, works exactly as described but the
          delay can be upwards of 15 seconds. Depending on the speed of your motors
          you may want to decrease the resistor size, I tried 2M and 200K they seem
          fairly reasonable.

          The series diode driving M2 is that used to compensate for the other motor
          being driven by the AC240? adding the diode should bring the motors closer
          to the same speed.

          It would also be a simple matter to add a tactile sensor to force the turn,
          help to keep it from getting stuck.

          GrantM.

          "Brought to you by Batterybotics Ltd."


          At 12:02 AM 4/1/2003, you wrote:
          >Hi Ryan,
          >
          > I just couldn't resist cooking up an example of a phototaxis following bot.
          >
          >The attached circuit has photobridge LDR1 mounted in front and LDR2
          > in the rear. The delay cicruit is the special bicore I posted earlier
          >which lends itself to this application. The bicore generates a long run
          >delay and a short spin delay. Both delays are influenced by the
          >resistance ratio of the LDRs which depends on the ratio of light
          >front to back. If LDR1 is brighter than LDR2, the delay is longer
          >and vice versa. When the short delay is active Beamus spins for a
          >short random time (<1sec) before it times out and Beamus starts
          >rolling straight forward in a random direction for the duration of the
          >longer (1-10sec) run delay. The run delay times out quickly if the
          >light gradient is stronger back to front and times out slowly if the
          >light gradient is stronger front to back as determined by the ratio
          >of the LDR rsistances . The two caps and the 1M /10M resistors
          >can be changed to suit for different delays and sensitivity.
          >With the photo gradient dependent delay time and random
          >motion this bot will eventually converge on the brightest light even in
          >a complex or random environment.
          >
          >wilf
          >
          >
          >----- Original Message -----
          >From: <mailto:wilsonryanj@...>Ryan W
          >To: <mailto:beam@yahoogroups.com>beam@yahoogroups.com
          >Sent: Monday, March 31, 2003 9:08 PM
          >Subject: Re: [beam] phototaxis
          >
          >I was thinking of two photo sensors, one on the front,
          >one on the back. compare the difference, if there is
          >more light on the 'head' then longer run, more light
          >on the 'tail' then shorter run.
          >
          >Ryan
        • wilf rigter
          Hi Grant, Thanks for trying this circuit out. Can you describe how effective the random spinning part is? How long does it rotate before a new direction is
          Message 4 of 22 , Apr 1 11:32 AM
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            Hi Grant,
             
            Thanks for trying this circuit out. Can you describe how effective the random spinning part is? How long does it rotate before a new direction is selected? 
             
            Yes, the diode in series was added to equalize the speed of the two motors. If the motors are not running at the same RPM the run motion will be in an arc. Whether or not this is required is a matter of trial and error. In any case this was just the basic circuit. If a h-bridge is used or if two 240 inverters are sufficient,  the remaining  inverters can be used for all kinds of add-on circuits for obstacle detection, etc . 
             
            wilf
            ----- Original Message -----
            From: GrantM
            Sent: Tuesday, April 01, 2003 10:34 AM
            Subject: Re: [beam] phototaxis

            Morning!

            Just did a quick test of Wilf's circuit, works exactly as described but the
            delay can be upwards of 15 seconds. Depending on the speed of your motors
            you may want to decrease the resistor size, I tried 2M and 200K they seem
            fairly reasonable.

            The series diode driving M2 is that used to compensate for the other motor
            being driven by the AC240? adding the diode should bring the motors closer
            to the same speed.

            It would also be a simple matter to add a tactile sensor to force the turn,
            help to keep it from getting stuck.

            GrantM.

            "Brought to you by Batterybotics Ltd."


            At 12:02 AM 4/1/2003, you wrote:
            >Hi Ryan,
            >
            >  I just couldn't resist cooking up an example of a phototaxis following bot.
            >
            >The attached circuit has photobridge LDR1 mounted in front and LDR2
            >  in the rear.  The delay cicruit is the special bicore I posted earlier
            >which lends itself to this application. The bicore generates a long run
            >delay and a short spin delay. Both delays are influenced by the
            >resistance ratio of the LDRs which depends on the ratio of light
            >front to back.  If LDR1 is brighter than LDR2, the delay is longer
            >and vice versa. When the short delay is active Beamus spins for a
            >short random time  (<1sec) before it times out and Beamus starts
            >rolling straight forward in a random direction for the duration of the
            >longer (1-10sec) run delay. The run delay times out quickly if the
            >light gradient is stronger back to front and times out slowly if the
            >light gradient is stronger front to back as determined by the ratio
            >of the LDR rsistances . The two caps and the 1M /10M resistors
            >can be changed to suit for different delays and sensitivity.
            >With the photo gradient dependent delay time and random
            >motion this bot will eventually converge on the brightest light even in
            >a complex or random environment.
            >
            >wilf
            >
            >
            >----- Original Message -----
            >From: <mailto:wilsonryanj@...>Ryan W
            >To: <mailto:beam@yahoogroups.com>beam@yahoogroups.com
            >Sent: Monday, March 31, 2003 9:08 PM
            >Subject: Re: [beam] phototaxis
            >
            >I was thinking of two photo sensors, one on the front,
            >one on the back. compare the difference, if there is
            >more light on the 'head' then longer run, more light
            >on the 'tail' then shorter run.
            >
            >Ryan




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          • wilf rigter
            Meaning to mention this before and this goes for any of our beam critters: Beam Art Machines. If you mount one or more felt pens on the bot to trace out its
            Message 5 of 22 , Apr 1 11:44 AM
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              Meaning to mention this before and this goes for any of our beam critters:
               
              Beam Art Machines.
               
              If you mount one or more felt pens on the bot to trace out its random path on a large piece of paper,  the resulting picture may please the eye.  
               
              wilf
               
              ----- Original Message -----
              Sent: Tuesday, April 01, 2003 11:32 AM
              Subject: Re: [beam] phototaxis

              Hi Grant,
               
              Thanks for trying this circuit out. Can you describe how effective the random spinning part is? How long does it rotate before a new direction is selected? 
               
              Yes, the diode in series was added to equalize the speed of the two motors. If the motors are not running at the same RPM the run motion will be in an arc. Whether or not this is required is a matter of trial and error. In any case this was just the basic circuit. If a h-bridge is used or if two 240 inverters are sufficient,  the remaining  inverters can be used for all kinds of add-on circuits for obstacle detection, etc . 
               
              wilf
              ----- Original Message -----
              From: GrantM
              Sent: Tuesday, April 01, 2003 10:34 AM
              Subject: Re: [beam] phototaxis

              Morning!

              Just did a quick test of Wilf's circuit, works exactly as described but the
              delay can be upwards of 15 seconds. Depending on the speed of your motors
              you may want to decrease the resistor size, I tried 2M and 200K they seem
              fairly reasonable.

              The series diode driving M2 is that used to compensate for the other motor
              being driven by the AC240? adding the diode should bring the motors closer
              to the same speed.

              It would also be a simple matter to add a tactile sensor to force the turn,
              help to keep it from getting stuck.

              GrantM.

              "Brought to you by Batterybotics Ltd."


              At 12:02 AM 4/1/2003, you wrote:
              >Hi Ryan,
              >
              >  I just couldn't resist cooking up an example of a phototaxis following bot.
              >
              >The attached circuit has photobridge LDR1 mounted in front and LDR2
              >  in the rear.  The delay cicruit is the special bicore I posted earlier
              >which lends itself to this application. The bicore generates a long run
              >delay and a short spin delay. Both delays are influenced by the
              >resistance ratio of the LDRs which depends on the ratio of light
              >front to back.  If LDR1 is brighter than LDR2, the delay is longer
              >and vice versa. When the short delay is active Beamus spins for a
              >short random time  (<1sec) before it times out and Beamus starts
              >rolling straight forward in a random direction for the duration of the
              >longer (1-10sec) run delay. The run delay times out quickly if the
              >light gradient is stronger back to front and times out slowly if the
              >light gradient is stronger front to back as determined by the ratio
              >of the LDR rsistances . The two caps and the 1M /10M resistors
              >can be changed to suit for different delays and sensitivity.
              >With the photo gradient dependent delay time and random
              >motion this bot will eventually converge on the brightest light even in
              >a complex or random environment.
              >
              >wilf
              >
              >
              >----- Original Message -----
              >From: <mailto:wilsonryanj@...>Ryan W
              >To: <mailto:beam@yahoogroups.com>beam@yahoogroups.com
              >Sent: Monday, March 31, 2003 9:08 PM
              >Subject: Re: [beam] phototaxis
              >
              >I was thinking of two photo sensors, one on the front,
              >one on the back. compare the difference, if there is
              >more light on the 'head' then longer run, more light
              >on the 'tail' then shorter run.
              >
              >Ryan




              To unsubscribe from this group, send an email to:
              beam-unsubscribe@egroups.com



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            • GrantM
              Hi Wilf, With the verbatim values it would be between 4 and 15 seconds between direction changes. I breadboarded the circuit but did not put it on a mobile
              Message 6 of 22 , Apr 1 2:28 PM
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                Hi Wilf,

                With the verbatim values it would be between 4 and 15 seconds between
                direction changes. I breadboarded the circuit but did not put it on a
                mobile platform, so as for the effective randomness of the circuit I can
                not say.

                In an abstract way this is similar to the phototropism of the miniball, In
                that the distance towards light should end up being greater than away from
                light.

                GrantM.

                "Batterybotics?"


                At 11:32 AM 4/1/2003, you wrote:
                >Hi Grant,
                >
                >Thanks for trying this circuit out. Can you describe how effective the
                >random spinning part is? How long does it rotate before a new direction is
                >selected?
                >
                >Yes, the diode in series was added to equalize the speed of the two
                >motors. If the motors are not running at the same RPM the run motion will
                >be in an arc. Whether or not this is required is a matter of trial and
                >error. In any case this was just the basic circuit. If a h-bridge is used
                >or if two 240 inverters are sufficient, the remaining inverters can be
                >used for all kinds of add-on circuits for obstacle detection, etc .
                >
                >wilf
                >----- Original Message -----
                >From: <mailto:listmail@...>GrantM
                >To: <mailto:beam@yahoogroups.com>beam@yahoogroups.com
                >Sent: Tuesday, April 01, 2003 10:34 AM
                >Subject: Re: [beam] phototaxis
                >
                >Morning!
                >
                >Just did a quick test of Wilf's circuit, works exactly as described but the
                >delay can be upwards of 15 seconds. Depending on the speed of your motors
                >you may want to decrease the resistor size, I tried 2M and 200K they seem
                >fairly reasonable.
                >
                >The series diode driving M2 is that used to compensate for the other motor
                >being driven by the AC240? adding the diode should bring the motors closer
                >to the same speed.
                >
                >It would also be a simple matter to add a tactile sensor to force the turn,
                >help to keep it from getting stuck.
                >
                >GrantM.
                >
                >"Brought to you by Batterybotics Ltd."
              • Wilf Rigter
                Hi Grant, I expect it to spin
                Message 7 of 22 , Apr 1 3:09 PM
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                  Hi Grant,

                  I expect it to spin <1sec before veering off on a tangent.
                  Since the both spin and run delays are set by the LDR ratio and since that
                  is continuously changing as it spins, I expect the delay to be quite random
                  if it spins more than a few rotations before chosing a new direction.

                  Is that more or less how it behaves?

                  wilf

                  ----- Original Message -----
                  From: "GrantM" <listmail@...>
                  To: <beam@yahoogroups.com>
                  Sent: Tuesday, April 01, 2003 2:28 PM
                  Subject: Re: [beam] phototaxis


                  > Hi Wilf,
                  >
                  > With the verbatim values it would be between 4 and 15 seconds between
                  > direction changes. I breadboarded the circuit but did not put it on a
                  > mobile platform, so as for the effective randomness of the circuit I can
                  > not say.
                  >
                  > In an abstract way this is similar to the phototropism of the miniball, In
                  > that the distance towards light should end up being greater than away from
                  > light.
                  >
                  > GrantM.
                  >
                  > "Batterybotics?"
                  >
                  >
                  > At 11:32 AM 4/1/2003, you wrote:
                  > >Hi Grant,
                  > >
                  > >Thanks for trying this circuit out. Can you describe how effective the
                  > >random spinning part is? How long does it rotate before a new direction
                  is
                  > >selected?
                  > >
                  > >Yes, the diode in series was added to equalize the speed of the two
                  > >motors. If the motors are not running at the same RPM the run motion will
                  > >be in an arc. Whether or not this is required is a matter of trial and
                  > >error. In any case this was just the basic circuit. If a h-bridge is used
                  > >or if two 240 inverters are sufficient, the remaining inverters can be
                  > >used for all kinds of add-on circuits for obstacle detection, etc .
                  > >
                  > >wilf
                  > >----- Original Message -----
                  > >From: <mailto:listmail@...>GrantM
                  > >To: <mailto:beam@yahoogroups.com>beam@yahoogroups.com
                  > >Sent: Tuesday, April 01, 2003 10:34 AM
                  > >Subject: Re: [beam] phototaxis
                  > >
                  > >Morning!
                  > >
                  > >Just did a quick test of Wilf's circuit, works exactly as described but
                  the
                  > >delay can be upwards of 15 seconds. Depending on the speed of your motors
                  > >you may want to decrease the resistor size, I tried 2M and 200K they seem
                  > >fairly reasonable.
                  > >
                  > >The series diode driving M2 is that used to compensate for the other
                  motor
                  > >being driven by the AC240? adding the diode should bring the motors
                  closer
                  > >to the same speed.
                  > >
                  > >It would also be a simple matter to add a tactile sensor to force the
                  turn,
                  > >help to keep it from getting stuck.
                  > >
                  > >GrantM.
                  > >
                  > >"Brought to you by Batterybotics Ltd."
                  >
                  >
                  >
                  > Yahoo! Groups Sponsor
                  > ADVERTISEMENT
                  >
                  >
                  >
                  >
                  > To unsubscribe from this group, send an email to:
                  > beam-unsubscribe@egroups.com
                  >
                  >
                  >
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                  >


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                • GrantM
                  Hello Wilf, One thing I did notice was that when pointed towards the light it would be longer between turns but the turn time was longer. When pointed away
                  Message 8 of 22 , Apr 1 5:50 PM
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                    Hello Wilf,

                    One thing I did notice was that when pointed towards the light it would be
                    longer between turns but the turn time was longer. When pointed away from
                    light the turns were more frequent but less severe.

                    So if the net amount of turning was the same would this actually be
                    phototropic?

                    GrantM.



                    At 03:09 PM 4/1/2003, you wrote:
                    >Hi Grant,
                    >
                    >I expect it to spin <1sec before veering off on a tangent.
                    >Since the both spin and run delays are set by the LDR ratio and since that
                    >is continuously changing as it spins, I expect the delay to be quite random
                    >if it spins more than a few rotations before chosing a new direction.
                    >
                    >Is that more or less how it behaves?
                    >
                    >wilf
                    >
                    >----- Original Message -----
                    >From: "GrantM" <listmail@...>
                    >To: <beam@yahoogroups.com>
                    >Sent: Tuesday, April 01, 2003 2:28 PM
                    >Subject: Re: [beam] phototaxis
                    >
                    >
                    > > Hi Wilf,
                    > >
                    > > With the verbatim values it would be between 4 and 15 seconds between
                    > > direction changes. I breadboarded the circuit but did not put it on a
                    > > mobile platform, so as for the effective randomness of the circuit I can
                    > > not say.
                    > >
                    > > In an abstract way this is similar to the phototropism of the miniball, In
                    > > that the distance towards light should end up being greater than away from
                    > > light.
                    > >
                    > > GrantM.
                    > >
                    > > "Batterybotics?"
                    > >
                  • Bruce Robinson
                    ... Hi, Wilf. Neither could I. :) I came up with this variation a couple of weeks ago, but a short vacation followed by a seminar got in the way of posting it
                    Message 9 of 22 , Apr 21 8:40 PM
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                      > wilf rigter wrote:
                      >
                      > I just couldn't resist cooking up an
                      > example of a phototaxis following bot.

                      Hi, Wilf.

                      Neither could I. :)

                      I came up with this variation a couple of weeks ago, but a short
                      vacation followed by a seminar got in the way of posting it sooner. I've
                      got this circuit working on the breadboard right now and I hope to try
                      it out with a couple of SB motors in the next week or two.

                      The robot will move in a straight line (more or less) as long as the
                      light level is rising or remains constant. When the light level starts
                      to fall, the robot will continue for a short distance (in case it's just
                      a small shadow) and will then switch to "brighter-seeking" mode. To seek
                      brighter light one motor stops long enough to make a 135 degree turn and
                      then starts up again. If the light level doesn't increase the
                      turn-then-pivot action continues until finally the light level starts to
                      rise.

                      If the robot bumps into something it will reverse bot motors for a short
                      period. Simply reversing away from an obstacle isn't usually a
                      successful strategy, but remember, when the robot reverses it will
                      experience a decreasing light level and one motor will stop. And if the
                      robot reverses into an object, sensors at the back will deactivate the
                      reverse delay and allow the robot to go forward again.

                      The motors are driven by a 74AC240, using two gates in parallel to drive
                      each motor lead. Additional chips can be stacked on top of the first one
                      if more current is needed. One motor driver is permanently enabled and
                      the other can be enabled for straight travel or disabled for turning.
                      Resistor R7 is a pulldown resistor that keeps one pair of inverter
                      inputs from "floating" when the motor is disabled.

                      The circuit uses a simple level detector consisting of and LDR in series
                      with a 10k resistor (R1), all connected between Vcc and Gnd. The voltage
                      tap between the LDR and R1 is fed directly to the (+) input of an
                      op-amp, and indirectly through a delay circuit (R2 & C1) to the (-)
                      input of the op-amp. The up-amp is therefore comparing the current light
                      intensity to the very recent intensity. As long as the light intensity
                      is increasing the output will be high; when it decreases the op-amp
                      output goes low. The responsiveness to changes in light level is
                      determined by R2 and C1. Lower values will cause the circuit to detect a
                      change in light level more quickly. The LDR is mounted pointing straight
                      up.

                      The output of the level detector is used to control a bicore. The bicore
                      might look a little unfamiliar at first -- to keep the chip count down I
                      used a pair of op-amps configured as ordinary inverters in place of
                      conventional inverters. It helps to visualize the circuit if you think
                      of each op-amp and 47k/22k resistor pair as an ordinary inverter. When
                      the level detector produces a high output (increasing light), the bicore
                      is locked up. In this state the bicore output enables the driver chip,
                      causing the robot to travel straight.

                      When the level detector produces a low output (decreasing light), the
                      bicore starts to run. R4 & C4 determine the time the robot turns (one
                      motor is disabled). R3 & C3 determine how long the robot runs in a
                      straight line after turning.

                      Reversing is controlled by a simple Nu neuron. Once again, an op-amp is
                      used in place of an inverter, this time configured as a Schmitt
                      inverter. The op-amp together with the 22k/47k/100k resistor network
                      behaves as a conventional Schmitt device. When either front sensor is
                      closed, after a brief delay (determined by R5) the driver signal to both
                      motors is inverted and any running motor is reversed. The reverse time
                      is determined by R6 and C6. If the robot backs into something the back
                      sensors are closed, shorting out the Nu neuron and restoring forward
                      motion.

                      The labelled components (R1, etc. ... C1, etc.) can be varied to suit
                      the motors. The unlabelled resistors used to turn the op-amps into
                      inverters can be varied, but the proportions should be kept
                      approximately the same.

                      While the circuit works well on the breadboard, I cannot vouch for it on
                      an actual robot. As always, be prepared for some unpredictable behaviour
                      when the circuit becomes mobile. It is a relatively simple 2-chip
                      circuit but it doesn't quite fit my definition of an interesting robot.
                      This one can't be left running for long periods of time because it will
                      very soon drain its batteries.

                      In reality I would probably add a 74HC14 chip to provide the control
                      logic (bicore & Nu) and use the freed-up op-amps as additional light
                      level detectors. In broad terms I'd make a robot that shuts down in the
                      dark, moves around intermittently in dim or very bright light, and
                      becomes very active in moderately bright light.

                      Enjoy,
                      Bruce
                    • Ori
                      Hey Bruce, I like the circuit! The entire idea of getting the sensory dada from a moment ago is a pain.... but what if you simplify the situation a bit? Say
                      Message 10 of 22 , Apr 21 9:14 PM
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                        Hey Bruce, I like the circuit!

                        The entire idea of getting the sensory dada from a moment ago is a pain....
                        but what if you simplify the situation a bit? Say that 'a moment ago' the
                        bot was 1 cm back... why not, then, put two LDRs on your bot, being 1 cm
                        apart, in front of each other?

                        Sure, it isn't always true that the rear sensor will have the same value as
                        the front sensor did 'a moment' earlier (Say the light source is someone
                        holding a flashlight, and that is being moved around...), but it might be
                        'good enough'...

                        And why isn't there a chip that finds the derivative of the input for us
                        anyways? :)

                        Or is there?

                        Ori

                        ----- Original Message -----
                        From: "Bruce Robinson" <Bruce_Robinson@...>
                        To: <beam@yahoogroups.com>
                        Sent: Monday, April 21, 2003 11:40 PM
                        Subject: Re: [beam] phototaxis


                        > > wilf rigter wrote:
                        > >
                        > > I just couldn't resist cooking up an
                        > > example of a phototaxis following bot.
                        >
                        > Hi, Wilf.
                        >
                        > Neither could I. :)
                        >
                        > I came up with this variation a couple of weeks ago, but a short
                        > vacation followed by a seminar got in the way of posting it sooner. I've
                        > got this circuit working on the breadboard right now and I hope to try
                        > it out with a couple of SB motors in the next week or two.
                        >
                        > The robot will move in a straight line (more or less) as long as the
                        > light level is rising or remains constant. When the light level starts
                        > to fall, the robot will continue for a short distance (in case it's just
                        > a small shadow) and will then switch to "brighter-seeking" mode. To seek
                        > brighter light one motor stops long enough to make a 135 degree turn and
                        > then starts up again. If the light level doesn't increase the
                        > turn-then-pivot action continues until finally the light level starts to
                        > rise.
                        >
                        > If the robot bumps into something it will reverse bot motors for a short
                        > period. Simply reversing away from an obstacle isn't usually a
                        > successful strategy, but remember, when the robot reverses it will
                        > experience a decreasing light level and one motor will stop. And if the
                        > robot reverses into an object, sensors at the back will deactivate the
                        > reverse delay and allow the robot to go forward again.
                        >
                        > The motors are driven by a 74AC240, using two gates in parallel to drive
                        > each motor lead. Additional chips can be stacked on top of the first one
                        > if more current is needed. One motor driver is permanently enabled and
                        > the other can be enabled for straight travel or disabled for turning.
                        > Resistor R7 is a pulldown resistor that keeps one pair of inverter
                        > inputs from "floating" when the motor is disabled.
                        >
                        > The circuit uses a simple level detector consisting of and LDR in series
                        > with a 10k resistor (R1), all connected between Vcc and Gnd. The voltage
                        > tap between the LDR and R1 is fed directly to the (+) input of an
                        > op-amp, and indirectly through a delay circuit (R2 & C1) to the (-)
                        > input of the op-amp. The up-amp is therefore comparing the current light
                        > intensity to the very recent intensity. As long as the light intensity
                        > is increasing the output will be high; when it decreases the op-amp
                        > output goes low. The responsiveness to changes in light level is
                        > determined by R2 and C1. Lower values will cause the circuit to detect a
                        > change in light level more quickly. The LDR is mounted pointing straight
                        > up.
                        >
                        > The output of the level detector is used to control a bicore. The bicore
                        > might look a little unfamiliar at first -- to keep the chip count down I
                        > used a pair of op-amps configured as ordinary inverters in place of
                        > conventional inverters. It helps to visualize the circuit if you think
                        > of each op-amp and 47k/22k resistor pair as an ordinary inverter. When
                        > the level detector produces a high output (increasing light), the bicore
                        > is locked up. In this state the bicore output enables the driver chip,
                        > causing the robot to travel straight.
                        >
                        > When the level detector produces a low output (decreasing light), the
                        > bicore starts to run. R4 & C4 determine the time the robot turns (one
                        > motor is disabled). R3 & C3 determine how long the robot runs in a
                        > straight line after turning.
                        >
                        > Reversing is controlled by a simple Nu neuron. Once again, an op-amp is
                        > used in place of an inverter, this time configured as a Schmitt
                        > inverter. The op-amp together with the 22k/47k/100k resistor network
                        > behaves as a conventional Schmitt device. When either front sensor is
                        > closed, after a brief delay (determined by R5) the driver signal to both
                        > motors is inverted and any running motor is reversed. The reverse time
                        > is determined by R6 and C6. If the robot backs into something the back
                        > sensors are closed, shorting out the Nu neuron and restoring forward
                        > motion.
                        >
                        > The labelled components (R1, etc. ... C1, etc.) can be varied to suit
                        > the motors. The unlabelled resistors used to turn the op-amps into
                        > inverters can be varied, but the proportions should be kept
                        > approximately the same.
                        >
                        > While the circuit works well on the breadboard, I cannot vouch for it on
                        > an actual robot. As always, be prepared for some unpredictable behaviour
                        > when the circuit becomes mobile. It is a relatively simple 2-chip
                        > circuit but it doesn't quite fit my definition of an interesting robot.
                        > This one can't be left running for long periods of time because it will
                        > very soon drain its batteries.
                        >
                        > In reality I would probably add a 74HC14 chip to provide the control
                        > logic (bicore & Nu) and use the freed-up op-amps as additional light
                        > level detectors. In broad terms I'd make a robot that shuts down in the
                        > dark, moves around intermittently in dim or very bright light, and
                        > becomes very active in moderately bright light.
                        >
                        > Enjoy,
                        > Bruce
                        >
                        > To unsubscribe from this group, send an email to:
                        > beam-unsubscribe@egroups.com
                        >
                        >
                        >
                        > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
                        >
                        >


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                        ----
                      • Wilf Rigter
                        Hi Bruce, A different algorithm in the two solutions and different results. Both bots initially spin for a time to chose a random direction. In the Beamus
                        Message 11 of 22 , Apr 21 11:49 PM
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                          Hi Bruce,

                          A different algorithm in the two solutions and different results.

                          Both bots initially spin for a time to chose a random direction.

                          In the Beamus Phototaxis design, the run time in that random direction is
                          proportional to the absolute light level falling on the LDR. After a period
                          of time, a new random vector is chosen and the process repeats. The result
                          is that Beamus P. will always converge on the brightest light source. No
                          tactile sensor reversing was included in my design but that is not central
                          to trhe phototaxis problem.

                          In your P. Roller design there can be (in theory) unlimited run-time in a
                          given direction, even towards a weak light source, as long as the light
                          level does not decrease. That means if the sun is shining brightly in the
                          opposite direction, your bot may chose instead to home in on a candle. Of
                          course unlimited run-time assumes that the bot travels in a perfectly
                          straight line which it won't, so that it will veer away the light target.

                          Never the less the result is that your bot will converge on a most uniformly
                          lighted area and will avoid an area of mixed brightness even though the
                          average brightness in that area may be higher that the uniformly lit area.

                          As a side note, a single Vcc/3 reference voltage can be used by several
                          opamps saving a few resistors.

                          regards

                          wilf


                          ----- Original Message -----
                          From: "Bruce Robinson" <Bruce_Robinson@...>
                          To: <beam@yahoogroups.com>
                          Sent: Monday, April 21, 2003 8:40 PM
                          Subject: Re: [beam] phototaxis


                          > > wilf rigter wrote:
                          > >
                          > > I just couldn't resist cooking up an
                          > > example of a phototaxis following bot.
                          >
                          > Hi, Wilf.
                          >
                          > Neither could I. :)
                          >
                          > I came up with this variation a couple of weeks ago, but a short
                          > vacation followed by a seminar got in the way of posting it sooner. I've
                          > got this circuit working on the breadboard right now and I hope to try
                          > it out with a couple of SB motors in the next week or two.
                          >
                          > The robot will move in a straight line (more or less) as long as the
                          > light level is rising or remains constant. When the light level starts
                          > to fall, the robot will continue for a short distance (in case it's just
                          > a small shadow) and will then switch to "brighter-seeking" mode. To seek
                          > brighter light one motor stops long enough to make a 135 degree turn and
                          > then starts up again. If the light level doesn't increase the
                          > turn-then-pivot action continues until finally the light level starts to
                          rise.

                          ------------------ snipped ---------------------




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                        • Bruce Robinson
                          ... Yes -- not an improved circuit, but a different one. ... Unless, of course, the light source is changing faster than the robot can converge :) I keep
                          Message 12 of 22 , Apr 22 8:04 AM
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                            Wilf Rigter wrote:
                            >
                            > A different algorithm in the two solutions
                            > and different results.

                            Yes -- not an improved circuit, but a different one.

                            >
                            > ... The result is that Beamus P. will always
                            > converge on the brightest light source. ...

                            Unless, of course, the light source is changing faster than the robot
                            can converge :) I keep finding that the real world trashes theoretical
                            motion every time.

                            > No tactile sensor reversing was included in my
                            > design but that is not central to trhe phototaxis
                            > problem.

                            I just through that in 'cause I had a spare op-amp.

                            > ... That means if the sun is shining brightly in the
                            > opposite direction, your bot may chose instead to home
                            > in on a candle. ...

                            One thing I learned with Hider is that what a robot "sees" is quite
                            different from what we see. In my version of a phototaxis circuit the
                            behaviour will depend very much on where the LDR "points". The current
                            plan is to point it straight up. Indoors that means the robot will try
                            to stay underneath any overhead lights and would pretty much ignore
                            candles. Sunlight will attract the robot in daytime but the location of
                            the illuminated area will change.

                            It would quite interesting to turn loose some similar robot bodies using
                            your circuit and mine.

                            > As a side note, a single Vcc/3 reference voltage can be used by several
                            > opamps saving a few resistors.

                            Good point. Thanks.

                            Bruce
                          • Bruce Robinson
                            ... Hmm. I thought it was simpler. One sensor y know. ... It will work, but the behaviour is different. The single sensor circuit responds to variation over
                            Message 13 of 22 , Apr 22 8:15 AM
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                              Ori wrote:
                              >
                              > The entire idea of getting the sensory dada
                              > from a moment ago is a pain....

                              Hmm. I thought it was simpler. One sensor y'know.

                              > ... but what if you simplify the situation
                              > a bit? Say that 'a moment ago' the bot was
                              > 1 cm back... why not, then, put two LDRs on
                              > your bot, being 1 cm apart, in front of each
                              > other?

                              It will work, but the behaviour is different. The single sensor circuit
                              responds to variation over time, whether caused by motion or changing
                              light conditions. Your modification responds to variations over
                              distance.

                              So you build one with your design and I'll build one with my design and
                              someday we might be in the same place at the same time and we can see
                              how they behave in the same environment.

                              > And why isn't there a chip that finds the
                              > derivative of the input for us anyways? :)

                              I suspect the LM324 could be configured to do it.

                              Bruce
                            • Ori
                              ... Well, I took *that* as a challenge :) I was thinking about it in school, and I came up with the simplest one-sensor lightseeking bot yet (One chip instead
                              Message 14 of 22 , Apr 23 1:52 PM
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                                > Hmm. I thought it was simpler. One sensor y'know.

                                Well, I took *that* as a challenge :)

                                I was thinking about it in school, and I came up with the simplest
                                one-sensor lightseeking bot yet (One chip instead of Grant's two/three chip
                                circuit, and Bruce's two chip circuit), assuming that it works (HUGE
                                assumption ;)

                                The idea is, in an area with no gradient to the lighting (equally lit), the
                                bot would waggle (That's the scientific term) side to side, gradually moving
                                forward.

                                Pulses towards the light are on for longer, however, than pulses away from
                                the light, so this bot would be phototropic.

                                Attached is the schem... I am sure that you all like the alliteration in the
                                circuit name? :)

                                Ori
                              • GrantM
                                Afternoon, Nov 7, 2002. That s when I tried exactly what you have shown. Sorry this is a no go. The frequency of oscillation will depend on the ambient light
                                Message 15 of 22 , Apr 23 3:51 PM
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                                  Afternoon,

                                  Nov 7, 2002.

                                  That's when I tried exactly what you have shown.

                                  Sorry this is a no go.

                                  The frequency of oscillation will depend on the ambient light level not the
                                  duty cycle, the net effect on the duty cycle is zero. Even if it is moving
                                  towards the light and the gradient is changing, the average light level
                                  will be the same regardless of moving towards or away.

                                  GrantM.


                                  At 01:52 PM 4/23/2003, you wrote:
                                  > > Hmm. I thought it was simpler. One sensor y'know.
                                  >
                                  >Well, I took *that* as a challenge :)
                                  >
                                  >I was thinking about it in school, and I came up with the simplest
                                  >one-sensor lightseeking bot yet (One chip instead of Grant's two/three chip
                                  >circuit, and Bruce's two chip circuit), assuming that it works (HUGE
                                  >assumption ;)
                                  >
                                  >The idea is, in an area with no gradient to the lighting (equally lit), the
                                  >bot would waggle (That's the scientific term) side to side, gradually moving
                                  >forward.
                                  >
                                  >Pulses towards the light are on for longer, however, than pulses away from
                                  >the light, so this bot would be phototropic.
                                  >
                                  >Attached is the schem... I am sure that you all like the alliteration in the
                                  >circuit name? :)
                                  >
                                  >Ori
                                • Ori
                                  ... WOW! Exactly the same? Not a single difference?? Weird. And cool! :) ... the ... What do you mean? It doesn t drive the motors in reverse.... so why would
                                  Message 16 of 22 , Apr 23 7:51 PM
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                                    > Afternoon,
                                    >
                                    > Nov 7, 2002.
                                    >
                                    > That's when I tried exactly what you have shown.

                                    WOW! Exactly the same? Not a single difference?? Weird. And cool! :)

                                    >
                                    > Sorry this is a no go.
                                    >
                                    > The frequency of oscillation will depend on the ambient light level not
                                    the
                                    > duty cycle, the net effect on the duty cycle is zero.

                                    What do you mean? It doesn't drive the motors in reverse.... so why would
                                    the net effect be zero?

                                    Even if it is moving
                                    > towards the light and the gradient is changing, the average light level
                                    > will be the same regardless of moving towards or away.

                                    What happens then?? I mean, when the light is increasing, the voltage at the
                                    resistor connection approaches about 0.55V. When the light is decreasing,
                                    the voltage approaches 0V. The closer to 1/2Vcc, the longer the pulses,
                                    so... when the bot makes the swing towards bright light, it should keep on
                                    swinging a bit longer, and when swinging away, it should stop earlier.

                                    Why does it not do that? Did you try different cap and resistor values?

                                    Ori

                                    >
                                    > GrantM.
                                    >
                                    >
                                    > At 01:52 PM 4/23/2003, you wrote:
                                    > > > Hmm. I thought it was simpler. One sensor y'know.
                                    > >
                                    > >Well, I took *that* as a challenge :)
                                    > >
                                    > >I was thinking about it in school, and I came up with the simplest
                                    > >one-sensor lightseeking bot yet (One chip instead of Grant's two/three
                                    chip
                                    > >circuit, and Bruce's two chip circuit), assuming that it works (HUGE
                                    > >assumption ;)
                                    > >
                                    > >The idea is, in an area with no gradient to the lighting (equally lit),
                                    the
                                    > >bot would waggle (That's the scientific term) side to side, gradually
                                    moving
                                    > >forward.
                                    > >
                                    > >Pulses towards the light are on for longer, however, than pulses away
                                    from
                                    > >the light, so this bot would be phototropic.
                                    > >
                                    > >Attached is the schem... I am sure that you all like the alliteration in
                                    the
                                    > >circuit name? :)
                                    > >
                                    > >Ori
                                    >
                                    >
                                    >
                                    >
                                    > To unsubscribe from this group, send an email to:
                                    > beam-unsubscribe@egroups.com
                                    >
                                    >
                                    >
                                    > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
                                    >
                                    >
                                    >
                                  • Jonathan Challinger
                                    its quite simple, really photoresistor drives transistor on one side of bot, transistor drives motor, other motor goes half speed would that work i am kinda
                                    Message 17 of 22 , Apr 23 8:09 PM
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                                      its quite simple, really
                                      photoresistor drives transistor on one side of bot, transistor drives motor, other motor goes half speed
                                      would that work

                                      i am kinda against large numbers of inverters to do simple functions

                                      -jonathan

                                      Ori wrote:
                                      Afternoon,
                                      
                                      Nov 7, 2002.
                                      
                                      That's when I tried exactly what you have shown.
                                          
                                      WOW! Exactly the same? Not a single difference?? Weird. And cool! :)
                                      
                                        
                                      Sorry this is a no go.
                                      
                                      The frequency of oscillation will depend on the ambient light level not
                                          
                                      the
                                        
                                      duty cycle, the net effect on the duty cycle is zero.
                                          
                                      What do you mean? It doesn't drive the motors in reverse.... so why would
                                      the net effect be zero?
                                      
                                       Even if it is moving
                                        
                                      towards the light and the gradient is changing, the average light level
                                      will be the same regardless of moving towards or away.
                                          
                                      What happens then?? I mean, when the light is increasing, the voltage at the
                                      resistor connection approaches about 0.55V. When the light is decreasing,
                                      the voltage approaches 0V. The closer to 1/2Vcc, the longer the pulses,
                                      so... when the bot makes the swing towards bright light, it should keep on
                                      swinging a bit longer, and when swinging away, it should stop earlier.
                                      
                                      Why does it not do that? Did you try different cap and resistor values?
                                      
                                      Ori
                                      
                                        
                                      GrantM.
                                      
                                      
                                      At 01:52 PM 4/23/2003, you wrote:
                                          
                                      Hmm. I thought it was simpler. One sensor y'know.
                                              
                                      Well, I took *that* as a challenge :)
                                      
                                      I was thinking about it in school, and I came up with the simplest
                                      one-sensor lightseeking bot yet (One chip instead of Grant's two/three
                                            
                                      chip
                                        
                                      circuit, and Bruce's two chip circuit), assuming that it works (HUGE
                                      assumption ;)
                                      
                                      The idea is, in an area with no gradient to the lighting (equally lit),
                                            
                                      the
                                        
                                      bot would waggle (That's the scientific term) side to side, gradually
                                            
                                      moving
                                        
                                      forward.
                                      
                                      Pulses towards the light are on for longer, however, than pulses away
                                            
                                      from
                                        
                                      the light, so this bot would be phototropic.
                                      
                                      Attached is the schem... I am sure that you all like the alliteration in
                                            
                                      the
                                        
                                      circuit name? :)
                                      
                                      Ori
                                            
                                      
                                      
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                                    • GrantM
                                      ... Well, That circuit was one of the variations, another used an LED as the sensor and another attempt was to change the duty cycle of one side. So often work
                                      Message 18 of 22 , Apr 24 11:17 AM
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                                        At 07:51 PM 4/23/2003, you wrote:
                                        > > That's when I tried exactly what you have shown.
                                        >
                                        >WOW! Exactly the same? Not a single difference?? Weird. And cool! :)


                                        Well, That circuit was one of the variations, another used an LED as the
                                        sensor and another attempt was to change the duty cycle of one side. So
                                        often work is shadowed by others, there are many inventions that have been
                                        simultaneously created, reminiscent of that "global consciousness" no?



                                        > >
                                        > > Sorry this is a no go.
                                        > >
                                        > > The frequency of oscillation will depend on the ambient light level not
                                        >the
                                        > > duty cycle, the net effect on the duty cycle is zero.
                                        >
                                        >What do you mean? It doesn't drive the motors in reverse.... so why would
                                        >the net effect be zero?

                                        By that I mean that it will move in a straight vector, wagging a bit from
                                        side to side.



                                        > Even if it is moving
                                        > > towards the light and the gradient is changing, the average light level
                                        > > will be the same regardless of moving towards or away.
                                        >
                                        >What happens then?? I mean, when the light is increasing, the voltage at the
                                        >resistor connection approaches about 0.55V. When the light is decreasing,
                                        >the voltage approaches 0V. The closer to 1/2Vcc, the longer the pulses,
                                        >so... when the bot makes the swing towards bright light, it should keep on
                                        >swinging a bit longer, and when swinging away, it should stop earlier.
                                        >
                                        >Why does it not do that? Did you try different cap and resistor values?


                                        Ah yes. The pulse duration is determined by the light level falling on the
                                        photodiode, more so its the average light falling on the photodiode. It
                                        doesn't matter if the light level is increasing or decreasing the average
                                        will be the same.

                                        So what this will do is travel in a straight line and the amount of wag
                                        will depend on the ambient light level, cap and resistor values.

                                        GrantM.
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