Constructive day :D

Discussion in 'General Electronics Chat' started by happs, Mar 11, 2005.

  1. happs

    Thread Starter Member

    Feb 27, 2005
    24
    0
    Hey guys.

    Well since you lot have helped me learn so much and given me some good ideas and useful information in regards to my new found learning experience I thought I'd just let you know that I have come pretty far now!!

    Yesterday I finally figured out what op amps and comparators are about and throughout the day have been working on a temperature sensing circuit that works REALLY REALLY well. I used an LM339 comparator IC along with the rest of the usual bits n bobs and successfully made a four level temperature sensor. Using the four comparators inside the 339 I made four LED's light up one after the other as the temperature rises and drops. I am amazed how well it works and really pleased wit myself, heheh.

    Anyway, I am MAYBE jumping ahead of my abilities here, but it doesn't hurt to ask ... I would like to wire it up to a 7 segment display (1 is fine for now) and have the display go up and down (I don't mean show the temperature, just go up and down) depending on the conditions -- Is this possible with just four comparators ? I have a sneaky feeling that it isn't but that poses the question -- how to other temperature sensors work ?? They surely can't have like 100 comparators, each one sensing 1 degrees in temperature.
    Moving away from the comparator route if that isn't possible, how would I make the 7 segment display change without comparators ? If you guys know how it is done then please let me know, I don't want anyone to go to the trouble of drawing it all out for me, but maybe just give me a few pointers on how exactly temperature sensors work.

    Thanks in advance and thanks for all the previous help, it has been invaluable.

    - Alex
     
  2. mozikluv

    AAC Fanatic!

    Jan 22, 2004
    1,437
    1
    hi

    what you have already done is a temperature to voltage conversion. what you now want is to have the actual temperature displayed using 1 seven segment but that would limit your reading in centigrade scale of only 1 to 9 degrees. it could not even display a farenheit scale.

    i had that same problem before but thanks to the members they suggested i use a dot/bar display driver (LM3915) or the ICL7107 w/c i employed, i will also be trying the LM3915. however the ICL7107 is an expensive device, but on my part it's alright since am going to sell it to a client. :)

    but if you would like to make a digital voltmeter then use the 7107 and at the same time use it as a temp. display. :)
     
  3. happs

    Thread Starter Member

    Feb 27, 2005
    24
    0
    Hi mozikluv,

    Thanks for the input there :) I understand that a single 7 segment display would not work as an accurate temperature display, I was just wanting to see if I could get my circuit working with one just to see if I could, hehe :) I will check out the capabilities of the 3915 display driver -- I have some in my component box :) Thanks for the suggestions :D

    - Happs
     
  4. Nettron

    Member

    Jan 22, 2005
    29
    0
    Happs, congrats on getting your comparator temp sensor working, do you have a schematic you can post ?

    Appears you have already duplicated some of the circuitry inside a LM3914 (3915) bar/dot display driver IC. The 3914 contains ten comparators and a stable Vref, as well as current control so resistors are not needed on the LEDs.

    Since you are using comparators, the output is already digital ( high/low) so to drive a 7-segment display you'd need a decoder or more appropriately an encoder ( priority).

    IC drivers for a 7-segment display (to count from 0 to 9) usually require 4 inputs, so if you go with a flash type ADC built intirely from comparators you'd need a grand total of 16 comparators followed by a 16-to-4 priority encoder circuit ( a project within itself).
     
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