Saving ability for digital scale

Discussion in 'Homework Help' started by eric_s88, Apr 20, 2011.

  1. eric_s88

    Thread Starter Member

    Apr 20, 2011
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    Hi everyone, I'm Eric, and I'm new here!
    I'm planning to build a digital scale for my college project, I have the schematic for it, but I also want my scale have a memory to save weights!
    I have no idea, can anybody help me in finding memory circuit schematic? should I use a shift register or..?
    please HELP! :)
    Thanks.
    Eric.
     
    Last edited: Apr 20, 2011
  2. eric_s88

    Thread Starter Member

    Apr 20, 2011
    157
    1
    My digital scale information: 0~600g , using ICL7107 as an ADC, and 4 seven segments to display weight
     
  3. Georacer

    Moderator

    Nov 25, 2009
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    For how long do you want the data to be saved. How much data do you plan to save? How do you want to recall the saved data.

    All these question must be answered before you have start implementing your system. But I have a feeling you will end up with a microprocessor with a flash memory in the end...
     
  4. eric_s88

    Thread Starter Member

    Apr 20, 2011
    157
    1
    Hi Georacer thank you for your reply , I want to save data until the power is plugged, and I want just save 4 digit ( outputs of 7107 ). and I want to use a system like shift register: push a save button and Write the data, push a recall button and read data...
    the bad news is that I have no microprocessor experience, is it possible?? :(
     
  5. Georacer

    Moderator

    Nov 25, 2009
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    I don't know how you will wire your scale, that is your business, but I will assume that you have the binary output of tha scale available at certain pins. Is that what you are using?:
    http://www.intersil.com/data/fn/fn3082.pdf

    I 'll propose an IC solution, without using a μC. If I'm reading the datasheet correctly, the output towards the 7-segment arrays is comprised of 24 bits. You could use some registers with parallel load to store the 24bit information, and some MUXes to select either the output of the 7101 or the register lines to display. However, these are a lot of bits to handle. Without actually doint the calculations, I estimate you will need at about 12 ICs to handle it.

    What I am thinking about is to wire directly the output of the 7101 to the input of the registers. Wire the Load function of them to a push-button. Everytime you push it, the output will be stored into the registers. No need to debounce the push-button.
    As for the display, you will need to form somehow a 48-to-24 MUX. Its output will go directly to the 7-segs. It will take input from the 7107 and the registers. A button can toggle its select input to make it select one of the two inputs. No debouncing there needed either.

    I don't recommend the 74XX series for your project, as they are incompatible with your voltage supply. Maybe the 4XXX series would be more suitable. 4519 for the MUX and 4035 for the registers maybe?

    It would be nice if someone else could comment on this too.
     
  6. eric_s88

    Thread Starter Member

    Apr 20, 2011
    157
    1
    Yes thast the ADC I use for this project. I think I will need a 7segment to bcd code converter, because I have outputs for drive 7 segments on 7107 pins. So I have to connect outputs of 7107 to register and then a MUX will choose wich one(7107 or register) will be conected to 7segments, did I get right?

    Can I do the "reading scale" and "saving weight" jobs at the same time? I mean when I put a gauge on the scale and read for example 100g, at the same time push a button and have this saved..? am I right or...?

    Thank you a lot for your help :)
     
  7. Georacer

    Moderator

    Nov 25, 2009
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    You got the idea right, that's what I have in my mind too.
    The two actions, saving the value and selecting input are independent.

    I didn't mean to use the BCD-to-7seg converter, but rather give the raw 7-seg data to the registers and the MUX. Your idea, however, can save you some room.
    If you first encode the 7-seg output of the 7107, you can shrink the data line to 15bits. That way you can reduce drastically the amount of ICs you will use for selection and storage. You should, however decode it again before giving it to the 7-segments for display.
    In that way, you must use 3 BCD encoders, 3 decoders, 2 8bit registers and 4 quad 2-to-1 MUXes. 12 IC's in total. For your case, it turns out to be the same amount of ICs either way, but for larger data, it can save you some space.
     
  8. eric_s88

    Thread Starter Member

    Apr 20, 2011
    157
    1
    Oh yes, with converting those codes to bcd I will have to use many ICs, so your suggeted way is much more better and its easy to undertand, but forming a MUX to select wich one outputs (7107 or register) will go to display, is a bit confusing... thank you for your supporting I will be back If I had any problems ;) merC :)
     
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