Senior Project Light Sensor Ideas.

Discussion in 'The Projects Forum' started by nickels293, Dec 20, 2009.

  1. nickels293

    Thread Starter New Member

    Nov 21, 2008
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    So I'm working on building my Senior Project for Undergraduate Electrical Engineering and we're having a problem with light sensors. The robot will display emergent behavior and we specified that when a loud noise is heard the robot would run to the darkest area it can find(without using mapping). We're looking for a sensor to find the dark areas of a room but can't find one that works very well. I have tried a photocell but we're looking for something that is more directional where as the photocell just detects what is on the sensor. does anyone have any ideas on how to detect light from a distance or detect directional light if its possible?
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    Sounds like you need to look into aperturing to make your light detector more directional.

    hgmjr
     
  3. hobbyist

    Distinguished Member

    Aug 10, 2008
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    There shouldn't be any problem with using any kind of light detecting sensor, photo resistor, or photo transistor, design the output as an inversion, that as long as light is detected the output signal is high to run the locomotive factor (wheels or legs,ect...) then when light is reduced to some threshold value, the output shuts down.

    This is probably what your planning on doing any how, but I don't see why the need for directional lighting, when any lighting falling on the sensor should indicate that the vehicle must continue to move about until that sensor no longer has light on it.

    I think the key is to design a threshold value that the sensor must rerach and then bilateral switch to opposite condition, avouiding any ambigouty, state.

    Maybe I'm misundeerstanding what your asking about,
    sorry if I am..
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    I love it - that is going to be a robot cockroach.
     
  5. hgmjr

    Moderator

    Jan 28, 2005
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    You can call it robo-roach.

    hgmjr
     
  6. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Use a rotating mirror with encoding disc, lens, cadmimum sulfide photo-cell. Look for highest output voltage and go.
     
  7. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Just field tested idea-works; tried three different cells, one a JEM cell-49 years old,ohm-meter was detector. 20 RPM about right. If a sweeping motion is used, rotating mirror eliminated, but robot would have to rotate to give 360 coverage.
     
  8. nickels293

    Thread Starter New Member

    Nov 21, 2008
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    0
    Thank you all for your replies. The directional feature is needed so that the robot isn't aimlessly wandering around. We want it to demonstrate intelligence and in order to do this we would like to be able to detect light from a distance in a certain direction.
     
  9. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Direction control:using CdS cell with rotating mirror or rotating cell with slip rings, feed cell with constant current, output into emitter follower, output split between + input to comparator & peak V follower [diode,cap, & slow discharge resistor] to - input of comparator.As cell rotates ,capacitor charges up to peak - diode drop as refferance V, peak V on each revoluyion then gives comparator a + output giving a relative bearing of robot to darkest direction. Rotate robot to decrease bearing to 0. If it is desired to store bearing inf., use a counter[/32?]updated by code wheel,reset on ea. rev. @ 0 deg relative. Load a register from counter @ each comparator output. A print would be simpler, but i'm on a borrowed lap-top in sunny CA, with no scan.
     
  10. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Here is a print backing up my last post. Still using a rotating mirror to direct light on to a light dependent resistor, LDR, to give 360 deg. coverage. High order bit from register is lo 0-180 deg, hi 181-360 deg. Three outputs give straight ahead, left,L, & right, R, up-dated every revolution. If desired, Q4 can be decoded to drive a ring of LEDs to show relative bearing of of dark corner. Code wheel has two tracks, outer track 8, 16 or 32 segments, inner one, one for reset to indecate front direction. Robot will rotate ,try to straighton out, over-shoot, reverse direction in a damped directioanl oscillation, kinda like bowling bumper ball. Questions ?, just ask.
     
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