Weight activated LED

Discussion in 'The Projects Forum' started by electronics14, Sep 14, 2013.

  1. electronics14

    Thread Starter New Member

    Sep 14, 2013
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    Hi everyone! I am looking to build a circuit that will light an LED but is triggered by weight. I would want the light to reset at night. So the light would be turned on when the weight is sensed then remain on even after the weight is removed. Do you have any tips or advice? I don't know where to start! Thanks! :)

    Have a good day :)
     
  2. wayneh

    Expert

    Sep 9, 2010
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    How much weight? So the light would trigger once when the weight limit is exceeded, and then stay on until "dark" (how dark?, dusk, like a solar light?). Once the light is off in the dark, should it be ready to come back on immediately, or wait until there is light?

    If you don't mind, what are you doing? Smart folks here might come up with a clever solution.
     
  3. Metalmann

    Active Member

    Dec 8, 2012
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    The weight of a roach, or the weight of a human?
     
  4. electronics14

    Thread Starter New Member

    Sep 14, 2013
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    My idea was to have a sensor in a dog bowl that detects when the dog was fed and lights an LED alerting that the dog was fed. Then at the end of the day it reset so it can do the same thing. So the LED would need to stay lit even after the dog has eaten the food.

    Thanks for responding!
     
  5. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    You can make a simple 'scale' by making a capacitor. Two sheets of aluminum foil (30 cm x 30 cm each) with a piece of felt in between (35 x 35 cm). Use alagator clips to attach the foil to the circuit.

    The capacitance will increase as the pieces of foil are moved closer together. You will have capacitance in the 10 nF range but will depend on the thickness of your felt (foam or other compressible thin materials will work too).

    Then you can assemble these building blocks...
    Use a 555 timer with frequency of 30k hz (or more)

    Build a high pass filter circuit (with the scale as the capacitor). It should block most of the 555 timer signal when the scale is light (low capacitance). Then allow a signal to pass when the weight of the dog food is on it (Higher capacitance).

    Peak detector to trigger an LED when a threshhold signal strength is passed (from the filter).

    A reset button to discharge the peak detector when you get home at night.

    Not a simple project but it can be done if you break it down into parts. Experiment on a breadboard with each stage until it does what you want.

    I am sure other weighing sensors are available but I didn't know your budget. I liked the foil idea because it keeps the bowl flat and no moving parts. If you want something more simplified, try a ketchup packet with a corner torn off - place that under the bowl. If there is ketchup squirted under the bowl, the dog was fed.
     
    Last edited: Sep 15, 2013
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  6. wayneh

    Expert

    Sep 9, 2010
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    You want to detect the removal of food, or that the dog had been standing there? (Big weight difference)

    Why not just use a motion detector set to an "infinite" delay, so that the light never goes out until you reset it?
     
  7. trader007

    Active Member

    Feb 27, 2010
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    I think the OP wants a light to come on when food is put in the bowl, and remain on for the day. that way, when the dog eats the food, there light is there to tell people not to feed the dog again.

    the light will go off at night, so the next day when the bowl is empty and the light is off it will tell people the dog hasn't been fed for that day.
     
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  8. wayneh

    Expert

    Sep 9, 2010
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    Oh! In that case I'd just use a switch. You'd have to horse around a little with the mechanics of it, so that a full bowl easily triggers it but a lick from the hungry, unfed dog does not. On that last issue, I think a good debounce is going to be needed for whatever solution is chosen. Paw strikes, passing vermin, all sorts of things might cause a brief false positive.
     
    Last edited: Sep 16, 2013
  9. Metalmann

    Active Member

    Dec 8, 2012
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    I've had several dogs over the years, and never once needed a light to remember when they were fed??:eek:
     
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  10. electronics14

    Thread Starter New Member

    Sep 14, 2013
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    This is EXACTLY what I'm looking to do! :)
     
  11. electronics14

    Thread Starter New Member

    Sep 14, 2013
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    I am doing this for a project and I got the idea because sometimes people would feed the dog when they left for work and not tell anyone else so if he ate all the food you wouldn't know if he was fed. My dog is always fed though :)
     
  12. wayneh

    Expert

    Sep 9, 2010
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    If the person feeding the dog turned on a timer, say 16hr, with a switch when it was done, I assume that would work? Just thinking that you don't really need to detect the light level, you just need the light to go off at midnight, or whatever. Or some hours after the feeding.

    I understand the need to automate, so as to not require the operator to remember to hit the switch.
     
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