temperature display problems

Discussion in 'Homework Help' started by oli5787, Jun 16, 2009.

  1. oli5787

    Thread Starter New Member

    Jun 16, 2009
    5
    0
    Hello,

    i am new to the forum, and i am in need for urgent help.

    For my final ECAD project in my foundation degree i have been set the challenge of designing a circuit to display temperature and sound an alarm if the temperature is greater than 40 degrees between 8am and 12 noon.

    the clock i have constructed fine and it works correctly. the problem i am having is designing a temperature circuit that can use an LM35 or simular component to display the temperature on a 7 segment display. the issue is that i am not allowed to use a PIC and all my previous projects have used them.

    i am using the Proteus V6.9 simulation package if this helps

    any advice or information would be grateful

    Oliver
     
  2. RiJoRI

    Well-Known Member

    Aug 15, 2007
    536
    26
    Remember that microcontrollers are made up of circuits that were discrete long before they were incorporated into micros!

    You'll probably need a buffer between the sensor and the rest of the circuit. Then some type of A/D converter, then something to convert the digits into 7-seg data.

    You'll also need to define the temperature range you'll need to cover, and how sensitive your equipment needs to be: do you take 1 degree, 2 degree, 5 degree steps?

    What kind of A/D converter are you going to use? THere are probably a gazillion circuits on the Net with different kinds of A/D converters, and just as many LM35 circuits.

    My first approximation for this was to buffer the sensor with an opamp, feed that into a set of window comparators, which feed into the address lines of two EPROMs. The EPROMs have the patterns needed for the seven-segment displays. THis is a crude solution, but I would then take and improve the different parts.

    --Rich
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Or you use a parallel output A to D and latch the conversion into some IC's that have outputs going to BCD to 7 segment drivers.
     
  4. oli5787

    Thread Starter New Member

    Jun 16, 2009
    5
    0
    Thank you all for your input it was greatly appreciated,

    does any have an example circuit i can work from because i am really strugglyinh to design this circuit as silly as it may sound it has completlt baffeled me. all the circuit designs i have tried are reiggled with faults and i am unsure as ot why. i have attached 2 screen shots of the half built circuit for the temperature display.

    the 7 segments must display form 0 to 50,
    any one who can help i would be more than greatful.

    Regards

    OLLIE
     
  5. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    You are feeding an analog signal into a digital circuit.
    This will not work.
    There has to be a conversion from analog to digital.

    Greetings,
    Bertus
     
  6. oli5787

    Thread Starter New Member

    Jun 16, 2009
    5
    0
    So what am i meant to be using?? because i thought if i fed the analogue temperature sensor into the comparator and then compared it to an R/2R circuit then the comparator could be able to give a digital out??????
     
  7. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Hello,

    When comparing, the counters must be synchronized.
    This can be done by resetting both counters (for the display and dac).

    Sorry for not seeing the dac.

    Greetings,
    Bertus
     
  8. oli5787

    Thread Starter New Member

    Jun 16, 2009
    5
    0
    Hi,

    thats fine, so when you say all the counters do you mean the 390s and the 163's must all have the same clock pulse? how doe i turn th output of the comparator inot a pulse for the clocks to run on? can you see any major reasons why it will not work as i am having pages of errors from proteus atm.
     
  9. oli5787

    Thread Starter New Member

    Jun 16, 2009
    5
    0
    Hello,

    i have completed the circuit however i have an issue with the counter resetting mid coutn can any one offer any insight inot this i have attached the circuit diagram
     
  10. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,347
    Helllo,

    You must create a loop.
    1) Reset the counters.
    2) start counting.
    3) Latch to display when count temperature reached (output comparator).
    Goto 1)

    Greetings,
    Bertus
     
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