Help with an idea

Discussion in 'The Projects Forum' started by AWHATT1, Jan 29, 2013.

  1. AWHATT1

    Thread Starter New Member

    Jan 29, 2013
    Hi this is my first post ! I have had an idea in my head for a while but not really sure how to create it . I am an electrician and do have some experience with electronics but not with designing circuits. What I need is some help to create a circuit that users can input a desired weight (in grams) . when the the set weight is reached an output is switched . I'm sure this is very simple but I don't know where to begin . Any help would be much appreciated . Thanks .
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    A microprocessor/LCD screen/momentary push button. (and whatever is required to "switch" your output "load")
  3. Macgiver007

    New Member

    Jan 17, 2011
    Correction: the IC is the 567 TONE DECODER.
  4. Ron H

    AAC Fanatic!

    Apr 14, 2005
    Come again?:confused:
  5. thatoneguy


    Feb 19, 2009
    Is the desired mass fixed, or adjustable?

    Does the user need a display, or just an LED indicating enough has been placed on the plate?

    You'll want to start by looking at strain gauges and mounting. Here is a link that uses a Microcontroller (Atmel), but the strain gauge info is what you need most. (Watch the Video)

    If no display is needed, and you have/can make a calibration weight, this could be done with a comparator and potentiometer. There would be no option for a readout.

    For a display, and adjustable readout, you could use one of the beginner microcontroller packages that are quick to get going if you have any background in programming. Arduino (Programmed in C) and PICAXE (Programmed in BASIC) are the two main platforms, though there is the Basic Stamp (Also programmed in BASIC, but very much over-priced, IMO).

    Do you have any special requirements, such as very small or very large physical size? What range should the scale be capable of, and with what accuracy? What is the switched output, such as voltage @ with ? current ability, relay contact, or other?
    Last edited: Jan 29, 2013
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  6. strantor

    AAC Fanatic!

    Oct 3, 2010
    how much is your time worth? there is a wide array of commercially available products which will do what you want for under $300 dollars. If you're an electrician, you can make that much in a day & a half, whereas designing such a thing might take months. google "strain gauge panel meter relay output."
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  7. DickCappels


    Aug 21, 2008
    The simplest solution to the problem as described seems to be:

    Put two buckets on a beam, the center of the beam rests on a fulcrum.

    Place a microswitch the ground or on the table under the end of the beam at which the first bucket is located.

    Place a counter weight in one bucket.

    Begin adding the material to be measured to the second bucket.

    As the mass of the material in the second bucket approaches that in the first bucket, the first bucket will lift, causing the microswitch will change state.

    To reprogram for different masses merely change the counterweight and/or move the fulcrum along the beam.
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  8. AWHATT1

    Thread Starter New Member

    Jan 29, 2013
    Thank you for your ideas so far. Originally I had thought of using a balance beam with a micro switch, but decided it would be better if it could be done digitally as it would be impractical to keep changing the counter balance. The 'strain gauge panel meter relay output' looks like it would do the job but I was hoping to build something from scratch so I could get a better understanding of how it works, and hopefully learn something about designing circuits.
    My idea is to feed the product onto the load cell/strain gauge, once the desired weight is reached an output will energise a relay that will stop the feed and start the dispensing. It would be good to have a display that shows the selected set point.
    I would like to keep it as simple as possible.
    Thanks again.
  9. GetDeviceInfo

    AAC Fanatic!

    Jun 7, 2009
    check into comparators. Dial in your reference setting with a pot.
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