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Help amplifying a tiny current

Discussion in 'General Electronics Discussion' started by Avondale, Sep 4, 2016.

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  1. Avondale

    Avondale

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    Sep 4, 2016
    Hi ElectronicsPoint


    I have a temperature sensor module and i want to use it to activate a relay
    the 3v coin battery on the temp sensor works great, the output turns on when the selected temperature is reached
    when the 3v coin battery is used on the relay works great and feeds through 70mA roughly
    when i join both together there is only 10mA going through the relay from the temp sensor
    the relay wont fire at this amount and i need to figure out how to amplify it
    i am a beginner at components but i have tried a transistor and got it up to 50mA but it refuses to go higher

    I have attempted to draw out the circuit, please advise : D
    [​IMG]
     
    Last edited: Sep 4, 2016
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    This may be helpful.
     
  3. Avondale

    Avondale

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    Sep 4, 2016
    thanks @(*steve*)
    i have a question about what VCC would represent and what the unmarked input would represent
     
  4. Avondale

    Avondale

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    Sep 4, 2016
    i have drawn up a representation of it!
    check original post
     
  5. Alec_t

    Alec_t

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    The schematic editor in LTspice (free download from Linear Technology) is easy to use. You can also simulate the circuit operation (though learning how to do that well is a bit daunting).
     
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  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    It's best not to edit your posts to add stuff because we don't get notification and it becomes harder to read the thread.

    It would be useful to get some information about the "temperature switch". The circuit you've drawn *may* be ok, but since it doesn't work there's more we need to know.
     
  7. Avondale

    Avondale

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    Sep 4, 2016
    sure!
    [​IMG] [​IMG] (missing the actual temp sensor on the end)

    works great, outputs 3v when temp resistance is more than adjusted resistance (i believe that's how it works)
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    ok, the next step is to connect the battery to the relay and read the voltage across the battery when it is connected.
     
  9. Avondale

    Avondale

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    Sep 4, 2016
    2.12v
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    2.12V is really low.

    can you try the circuit you have using a stiffer 3V supply, say 2 x AA batteries?
     
  11. Avondale

    Avondale

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    Sep 4, 2016
    that helps! 3v
     
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Is it behaving better?
     
  13. Avondale

    Avondale

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    Sep 4, 2016
    i'm trying to get a reading on the mA coming out of the transistor now but there's too many wires to hold together lol
     
  14. Avondale

    Avondale

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    Sep 4, 2016
    now i'm getting 1.5v through the relay from the transistor
     
  15. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Do you want the relay energized when the led on that module is on or off?
     
  16. Avondale

    Avondale

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    Sep 4, 2016
    it seems to go off when the temperature goes above setting, which is when i would like the relay to activate
     
  17. Avondale

    Avondale

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    Sep 4, 2016
    i guess things are not as simple as i previously thought them to be : p
     
  18. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    The LM393 is open collector logic. This means it can't source current. Because of this your base drive current will be totally dependent upon the value of the pullup resistor connected to "DO". Since the output LED lights when 393's output pin goes low (not high) I would think that you should be using a PNP transistor with its Emitter connected to Vcc and the relay coil connected between the collector and GND. You will still need a series connected base resistor to limit base current.

    Chris
     
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  19. Alec_t

    Alec_t

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    Relays are current-hungry devices. Could you use a FET instead for switching a load?
     
    Last edited: Sep 4, 2016
    (*steve*) likes this.
  20. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Here's a schematic of what I described in my last post. I do have a question that i don't think anyone asked you. What's the operating Voltage and Current rating of your relay. Relays under 5V are not common.

    Chris
    upload_2016-9-4_11-19-53.png
     
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