Water Detector-NE555?

Discussion in 'Homework Help' started by ISB123, May 21, 2014.

  1. ISB123

    Thread Starter Well-Known Member

    May 21, 2014
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    Hello,I've been assigned to build a Water Detector based around NE 555.
    The problem is I didn't get the schematics only parts required for building the sensor.So I guess I'll have to figure out how it works.

    On the page I got it says on the left side there is a transistor and 100K resistor,2x 1.5K and single 4.7K resistor,they together with NE 555 will form a Schmitt Trigger.The other side of IC represents the buzzer with: 10K,100k
    resistors and 10nF ceramic condenser. Elements that make the siren noise are Blink diode,390 Ohm resistor and 47uF condenser.

    I tried looking up on the internet for NE 555 IC buzzer,Schmitt trigger and similar but it kind of confused me even more.

    Cheers!

    Parts:
    1. Stripboard
    2. Transistor(BC556,BC557,BC558) PNP-1
    3. NE555-1
    4. Blink Diode-1
    5. Speaker-1
    6. Elec. Condenser 10uF 16V-1
    7. Elec. Condenser 47uF 16V-1
    8. Ceramic Condenser 10nF-1
    9. Resistor 300 Ω-1
    10. Resistor 390 Ω-1
    11. Resistor 1.5 KΩ-2
    12. Resistor 4.7 KΩ-1
    13. Resistor 10 KΩ-1
    14. Resistor 100 KΩ-2
    15. 9V Battery
    16. Sensor
     
  2. #12

    Expert

    Nov 30, 2010
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    In a homework problem, we require you to display some kind of effort.
    You might describe how you intend to make contact with the water, start a drawing of your best guess about the schematic, or describe how the buzzer works.
     
  3. ISB123

    Thread Starter Well-Known Member

    May 21, 2014
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    Hello,here is the water sensor.
    It should work by having 2 alu. foil strips next to each other so when water closes the circuit between those two foils it changes the resistance which "activates" pnp transistor which with ne555 forms Schmitt trigger.

    Now I have a question.On small manual it says that water will change the resistance on
    the water sensor so does that mean that my water sensor should be connected and not broken in two pieces like in my picture below.To change the resistance the current has to flow trough it all the time(not possible in my drawing below unless I connect the strips) so pnp transistor can pick up the change?

    Now i need to figure out how to make a schmitt trigger using ne555 and BC556.

    [​IMG]
     
  4. DickCappels

    Moderator

    Aug 21, 2008
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    So far so good. You have it right, keep the electrodes separated. The wording "...water will change the resistance on the water sensor..." , as you suspect, probably refers to the resistance between the electrodes decreasing when water bridges the gap.
     
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  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Do you have a V meter?
    How much of a resistance change is there between wet & dry? Try connecting a 100k Ω R in series with sensor, WS, & battery. Measure V drop across WS & R, dry & wet. Which is greater.? Across R? , try a smaller resistor & re measure. What is current? ; enough to turn on a PNP ?
     
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  6. ISB123

    Thread Starter Well-Known Member

    May 21, 2014
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    Unfortunately I don't have a V-meter.
    I'm going to post the whole manual here hopefully someone will be able to explain it to me.

    Cheers!
     
  7. ISB123

    Thread Starter Well-Known Member

    May 21, 2014
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    Here is the manual:

    What is Water detector and what its made of?It has a water sensor,its a piece of board with few lines that are connected in 2 pairs,one pair on one side and another on other side.These 2 form a field which reacts on every drop of water.
    Resistance of that sensor changes if it gets in contact with water.The change in resistance reflects onto a PNP transistor which with NE555 IC forms "Schmitt trigger" which activates the buzzer.The buzzer starts to make noise so we know that something is flooded.

    The buzzer is standard one which is generally used with NE555.Only thing that isn't standard is 390Ω resistor on pin 5 with electrolyte condenser 47μF and blink LE diode.That are new components that make a "police siren" sound.Usually to create that sound another NE555 was used,now we have simplified it more.

    Lets repeat.We have water sensor.Left side of the scheme with transistor,100KΩ,2x 1.5KΩ and single 4.7KΩ resistors,they together with NE555 form Schmitt Trigger.
    Other part of the board represents the buzzer with those elements:
    10KΩ,100KΩ and 10nF(0.01μF) condenser.
    Elements that make siren sound are: Blink LE diode,390Ω resistor and 47μF electrolyte condenser.

    Speaker should be 50-75Ω those are rare so we can put a resistor(33-56Ω) in series with speaker.Power supply is from 9V battery or 12V AC adapter.

    The problem is that it keeps saying look at the schematic but I don't have one.

    If someone has some ideas I would be glad to hear them!
     
  8. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    You can try something like this. It might work better with dirty water or high β transistor. Have fun.
     
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  9. #12

    Expert

    Nov 30, 2010
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    I'm thinking you would have better results with the reset pin. An NE555 needs 100 ua and a TLC555 needs less than 100 pa on the reset pin.

    Notice: This is only a concept drawing. It must be adapted to your needs if you use it.
     
    Last edited: May 23, 2014
    ISB123 and Bernard like this.
  10. ISB123

    Thread Starter Well-Known Member

    May 21, 2014
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    Thanks for you help guys!
    I have one question what is the difference between normal LED and Blink LED?I noticed that normal led costs like 0.15$ and blink costs like 2$.
     
  11. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    A blink diode blinks or turns on & off at a visable rate. It has a microscopic IC inside to controll flashing. It's a new word to me.
     
  12. ISB123

    Thread Starter Well-Known Member

    May 21, 2014
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    Here is the finished circuit.

    Bernard-Did you connect wire from pin 8 to pin 3 wire or did you just accidentally made them connect?

    Is everything properly connected?

    [​IMG]
     
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  13. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    You are right, no connection 3 to 8, but we need a connection from collector to pin 8. Nice drawing. If wet sensor is not low enough resistance to operate ckt. and you are allowed another PNP, can convert transistor to a darlington compound transistor. This ckt has the advantage of no current drain when idle. Using reset might give a draw of about 12 mA at idle.
     
  14. ISB123

    Thread Starter Well-Known Member

    May 21, 2014
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    Can I replace 300Ω Resistor with 330Ω one?Shop doesn't have any 300Ω.

    P.S.

    Just did the calculation.

    Vf= 2V
    If= 20mA
    Vcc= 9V

    R=9V-2V/20mA=0.35(390Ω)

    1/2W 390Ω should be fine?
     
    Last edited: May 26, 2014
  15. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    That will indeed be fine.
     
  16. ISB123

    Thread Starter Well-Known Member

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    Here is finished PCB.The professor gave me the scheme.I can post it here.

    [​IMG]
     
    Last edited by a moderator: May 30, 2014
  17. Bernard

    AAC Fanatic!

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    Does it work? I would like to see your schematic.
     
  18. ISB123

    Thread Starter Well-Known Member

    May 21, 2014
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    Here is the schematic.Its working but I'm not sure why its not making the siren noise it just makes a continuous siren sound it doesn't go up and down in volume?

    [​IMG]
     
    Last edited by a moderator: May 31, 2014
  19. Alec_t

    AAC Fanatic!

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    The siren sound won't rise and fall unless the LED is blinking. Is it?
     
  20. ISB123

    Thread Starter Well-Known Member

    May 21, 2014
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    LED is always blinking when its connected to DC. I'm going to check the connection maybe i miss connected something.
     
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