Help on electronics a-level project

Discussion in 'General Electronics Chat' started by Abraam, Mar 4, 2013.

  1. Abraam

    Thread Starter New Member

    Mar 4, 2013
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    for my project im building a circuit on a breadbaord which im trying to make "warn the driver when its cold outside" im doing this by building a 555 astable with an LED as the output, a 555 monostable to trigger the astable to stay "high" for a certain amount of time then go "low".
    my question is how do i link a thermistor to the monostable to the astable?
    o can build then seperatly but i dont know how to link them!!
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Don't understand why you want both an astable and a monostable. Do you want the circuit to stop blinking after a certain period of time?

    A comparator can detect the thermistor voltage and inhibit the 555 operation (keep Reset pin low) until the temperature drops below your desired warning temperature.
     
  3. Abraam

    Thread Starter New Member

    Mar 4, 2013
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    thanks for the reply and yes i do want the LED to stop blinking after a while or else it will just get ridiculously annoying..
    ive built the monostable and the astable but i dont know how to connect them together!
    (im still nooby with electonics)
     
  4. crutschow

    Expert

    Mar 14, 2008
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    Below is the basic hookup for the comparator and two 555 circuits. I didn't show the rest of the 555 circuit or the power connections since I figure you can take care of that. I can help you with some of the calculations if you like.

    Make sense?

    Cold Warning Ckt.gif
     
  5. Jaguarjoe

    Active Member

    Apr 7, 2010
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    What exactly is an "a-level" project?
    Is it a Freshman thing or a senior thing? I hope it's not Grad school.
     
  6. Abraam

    Thread Starter New Member

    Mar 4, 2013
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    is there any way of doing this without a comparator?
    an a-level is 2 years of college in the UK just before university..
    thanks for your replies!
     
  7. Jaguarjoe

    Active Member

    Apr 7, 2010
    770
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    A very small uP would do this. If you use something easy to program like a little Picaxe 08M2 and a DS18B20 sensor, you wouldn't need any other parts and could whip it together in no time..

    FWIW-You can use an op amp instead of the comparator. Either way, make sure the current through the T-mister is low enough to keep it from self heating.

    I can't think of any analog sensor that does not require some sort of signal conditioning.
     
  8. crutschow

    Expert

    Mar 14, 2008
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    Why don't you want a comparator?
     
  9. MrChips

    Moderator

    Oct 2, 2009
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    I wish they had Electronics as a subject when I did my A-Levels. I would have aced it.
    Instead I had to take two Maths, Physics and Chemistry.
     
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