any change in light intensity for art project

Discussion in 'The Projects Forum' started by Cykar, Sep 24, 2012.

  1. Cykar

    Thread Starter New Member

    Sep 24, 2012
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    hi,

    i have a project i have been fiddling with for some time and trawling the web for something that'l help but i haven't had any success yet.

    The idea is simple: imagine a 10cm sheet of mdf, or wood, or plastic or whatever, with a hole in the middle containing an inset phototransistor. around the central hole, which is suitably screened, some leds. The idea is that any change in ambient light levels, whether darker or lighter, trigger the leds to go on, probably through a monostable 555 timer circuit. I have to filter out changes that are too slow, say over 2s, and ones that are too fast eg from lights.

    Then imagine i have 100 of these 'cells' all together, 10x10, on a wall like a painting, so as you go past, stand in front of it etc, you get a kind negative shadow, that dies away when any change is over. So you stand in front of it, see yourself, then see yourself fade away, since you then become the ambient light level for the phototransistors that can see you.

    so the sensitivity is important, and should work from up to 3m away ideally. The cost is important too, as obviously, the more cells I can afford, the greater the overall effect. I thought it would be a relatively easy thing to work out, but try as I might i cannot manage it, so i am here to ask for some help.

    oh, yes, I have tried ready made PIR sensors, but they do not really give me the required result, and are too expensive for the number I want anyway.

    i have attached the rudimentary circuit i was trying, but i'm afraid my knowledge is too scant to work out what I should be doing.

    [​IMG]

    Thanks for you patience.
     
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    It is an interesting idea, and might make an attractive artwork. I see two problems. First, I think that in order to achieve the shadow effect, you would need direct lighting from behind the person viewing the piece. I don't think that it would work well in ambient lighting. Second, the resolution would be rather poor with only 100 "pixels" to work with. It would be much more interesting if each LED had its own LDR control.
     
  3. wayneh

    Expert

    Sep 9, 2010
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    Ditto. I think you'll need to control the background - or should I say backlighting - so that the profile of the observer can be resolved. The light detectors need to be focused or placed in a tube so that they are directional. Otherwise, they won't be able to detect an edge.

    One thing that might work is IR illumination of the observer. They wouldn't see it, but a person standing in front of the work would then be very much brighter than his surroundings.

    But again, to detect an edge, you'll need a detector that "sees" only in a narrow beam.

    You could get really sharp edges by backlighting with focused IR beams shining on individual sensors, like on a garage door. Break the beam, a light comes on.
     
  4. Dodgydave

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    Jun 22, 2012
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  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Here's a start: Not bread boarded or tested, values just guesswork. Diodes , shottky, Si, Ge, or 20k resistors. +V, 5V to 12V. R7 depends on +V & LED. R3 & C1 determine time delay.
     
    Last edited: Sep 24, 2012
  6. tracecom

    AAC Fanatic!

    Apr 16, 2010
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    I am always amazed at how quickly you can draw those schematics.
     
  7. Cykar

    Thread Starter New Member

    Sep 24, 2012
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    wow, just got home and found all your responses.

    thanks to all.

    first, to help clarify, i am not really after a shadow, perhaps it was the wrong word to use. I know the definition would be poor if you regard it as something akin to a bitmap with pixels, but that doesn't really matter to me, it's about the fact that you are there, and as long as you move, it will light, reflecting your movement i suppose rather than your presence. In reality 10x10 would probably be larger than i would go, i was simply hedging my bets as regards making the actual things, fitting in the electronics etc. etc.

    I had made a circuit once before using an LDR that turned an led on, and it seemed to be very sensitive to small changes. it was housed in a black tube, which is pretty much what i was planning for the phototransistor, but it only worked in one direction as it were (less light), and whenever the ambient light changed significantly, i had to adjust the preset to account for it.

    using ir lights would i'm sure work, but i'm looking for something that might be a little simpler, and maybe require less installation.

    controling the background may, at a pinch be possible, but again, ideally this is something that i could pick up and put anywhere, and it would work. maybe asking too much?

    thanks for the circuit diagrams, i will get on to them as soon as I get a chance.

    i hope i can get back to you with some results soon.

    thanks again.
     
  8. Cykar

    Thread Starter New Member

    Sep 24, 2012
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    just wondered what is significant, or particular about the CA3140E op amp, (or CA3140AEZ improved version according to digikey). i have a number of opamp chips and am wondering if one of them may do the job
     
  9. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
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    I have used these for years for high impeadnce circuits like preamps, pico meter, volmeters, heartbeat monitors etc they are brilliant, the CA3240e is a dual version.

    Other op amps will do the job just as well.

    http://www.intersil.com/content/dam/Intersil/documents/fn95/fn957.pdf
     
    Last edited: Sep 24, 2012
  10. wayneh

    Expert

    Sep 9, 2010
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    Imagine a tiny being with its hand on the switch of each light you want to control. Let's call it Cykar's demon.

    How exactly do you expect Cykar's demon to decide when to turn the light on?

    With some computing power (the brain of Cykar's demon), you could probably have it watch ambient conditions for a while and self-adjust itself to ignore ambient. Similar to what you had to do manually with the potentiometer to adjust sensitivity. But I don't see how you can accomplish this simply and cheaply.
     
  11. tracecom

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    Apr 16, 2010
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    A simple IR sensor could detect a person's proximity, and start a microcontroller "polling" the individual sensors and turning on/off the associated LED's....Yeah, I know that's not "simply and cheaply," but it would be cool and would add all sorts of new possiblities.
     
  12. Cykar

    Thread Starter New Member

    Sep 24, 2012
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    i have managed to get a small change in voltage +- 10mV or so. I was imagining harnessing that change and amplifying it to the trigger the timer. is that not possible?
     
  13. wayneh

    Expert

    Sep 9, 2010
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    Against changing backgrounds and room conditions? Maybe a motion detector could, but I don't think just a LDR or phototransistor (my idea of simple) will be up to the job.
     
  14. Sensacell

    Well-Known Member

    Jun 19, 2012
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    I saw a similar project using an array of IR remote control receiver modules driving LED's, very simple, only 4 parts required: IR module, LED, current limiting resistor and a small bypass cap.

    The array was illuminated by a single IR LED (modulated at 32 khz) mounted about 6 meters away. The setup produced great crisp shadows of anything that crosses in between the LED and the array of sensors. Since it's using modulated IR, it has high immunity to ambient light.

    This whole delightful contraption was mounted in a small pedestrian underpass, to great effect.
     
  15. wayneh

    Expert

    Sep 9, 2010
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    Excellent solution.
     
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