Help needed with reservoir depletion warning system

Discussion in 'The Projects Forum' started by studentdesigner, Dec 7, 2014.

  1. studentdesigner

    Thread Starter New Member

    Dec 7, 2014
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    Hey,

    I'm afraid that this might be painfully simple, but I really am about as novice as they come with regards to electronics.

    I am currently working on a project and I need a little help, I'll try and make it as understandable as possible:
    • I'm making a product that features a reservoir that holds hand sanitiser fluid
    • The sanitiser is dispensed when a handle is pulled
    • I want a series of LEDs to light up when the fluid gets below a certain level in the reservoir (say the reservoir is 500ml and the LEDs are set to come on at 100ml)
    • However, I only want the LEDs to light up and stay lit for about 5 seconds after the handle is pulled
    • When the handle is pulled and the reservoir is above the level no LEDs will light up
    Is this possible? I imagine I would needs some sort of moisture sensor. I hope this makes sense. Any help would be greatly appreciated. Thanks!
     
  2. wayneh

    Expert

    Sep 9, 2010
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    Very possible. I think you can use a non-contact sensor to sense the liquid level. Maybe an optical method. Maybe even the weight of the reservoir.
     
  3. studentdesigner

    Thread Starter New Member

    Dec 7, 2014
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    By an optical method do you mean a laser type sensor or something? Do you think the circuit would look something like this, with two switches in series. I would also have to include some sort of timer like the 555 timer maybe?

    [​IMG]
     
  4. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    The sensor should be outside of the bottle. A gel is a mess to work with and does not flow well. A spring and switch in the frame of the mount with the bottle mounted on a pivot (only a small movement required for a membrane switch).

    That was just one example, there are many other ways but I would suggest trying to avoid putting any ultrasound or float or light sensors in the bottle.
     
  5. studentdesigner

    Thread Starter New Member

    Dec 7, 2014
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    Interesting. Thanks for your input. So it would be based on weight rather than moisture in the this case.
     
  6. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    As long as there is SOME liquid of a given concentration in a bottle, the humidity above that liquid is nearly constant. You won't be able to use humidity.
     
  7. Externet

    AAC Fanatic!

    Nov 29, 2005
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    A couple of ways that perhaps can work...
    - Being gel, it is probable that the container is a flexible reservoir. A microswitch can warn when the container is deformed/squeezed past a point.
    - A stroke counter. Can approximate the number of dispensing left in the reservoir.
    - A plain window cutout as some dispensers have. Allows visually evaluate the size of reservoir or amount left.
    If cannot cut out a window, get one with a window. ----> http://www.aspli.com/prdimgs/large/Spirigel-800ml-Soap,-or-San.jpg
    ----> http://thumbs4.picclick.com/d/w1600...SINGLE-CHAMBER-SOAP-SHAMPOO-GEL-DISPENSER.jpg

    Or ----> http://impactmedicalstrategies.com/kleengel-automatic-gel-dispenser/
     
  8. studentdesigner

    Thread Starter New Member

    Dec 7, 2014
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    Thanks for the feedback. The gel will be housed in a solid container, and filled from the top. I have considered the other options, but part of the appeal of having a lighting system was to add to the aesthetic of the product. I envisaged the LEDs running around the border of the product hidden behind frosted plastic to give a soft warning glow.
     
  9. wayneh

    Expert

    Sep 9, 2010
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    Yes, I was thinking of something like a break-beam detector you would use on a garage door. For this approach to work, you'd need a liquid that absorbs or scatters enough of the beam to make for easy and certain detection of whether the liquid is in the beam or not. This might take some research and experimentation. An advantage would be no moving parts and the electronics could be behind a washable surface.

    A pressure switch might be easier to get working quickly. Look up "roller switch". But you'd have to work out the mechanical details and think about how to keep it from getting gunked up.

    You're correct that a 555 circuit called the "one-shot" or "monostable multivibrator" will give you the 5 second on-time. This part is easy, although you'll need to think of a way to power it safely. If you don't care too much about the precision of the timing, there might be an even simpler circuit to consider.
     
  10. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Since the handle switch is in series with the sensor switch no timer is necessary: no pull, no light!
     
  11. crutschow

    Expert

    Mar 14, 2008
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    But he wanted it the stay lit for about 5 seconds after the handle is pulled.
     
  12. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    If the term "about" has a tighter tollerance then yes an accurate timer may be necessary.
     
  13. mcj74

    New Member

    Jan 10, 2007
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    Also consider a capacitive or inductive proximity sensor. When the liquid level falls below the sensor, the sensor's output will change. These are nice because it matters little what the liquid is. Then it's just a matter of designing the circuitry and calibrating it to "know" what the "full" and "empty" signal levels are. Could be done with trimpot-set operational amplifiers, or even a microcontroller (that's a whole other can of worms...)

    There are many "delay" circuits out there also. One (relatively imprecise) way would be with a transistor and capacitor. But any way this is approached, is going to take some experimentation.
     
  14. briselec

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    Sep 8, 2014
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