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Need help resistor values

Discussion in 'General Electronics Discussion' started by JVH, Oct 14, 2019.

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  1. JVH

    JVH

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    Oct 14, 2019
    Hi I am new to electronics and have a schematic I have coddled together . I would like some help
    with identifying two resistor values and any other mistakes I may have made . Will this circuit work after right values are added ? Any assistance is greatly appreciated .
    Forum post - Copy.png
     
  2. duke37

    duke37

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    Jan 9, 2011
    I would think that the BD140 is not necessary. T2 has to switch 44mA which most small transistors can manage. Look up the data sheets. I do nor remember all the numbers so I go for a 2N2222 which I can remember.
    Put the relay in T2 collector circuit. If you switch T2 fully on and off you will not need a heat sink.
    R1 could be about 1k. This would limit T2 base current to about 10mA
     
  3. Audioguru

    Audioguru

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    Sep 24, 2016
    Hee, hee. You have bats in your bedroom? Then do you live in a cave or in a tree?

    With pin 2, pin 6 and the capacitor of the 555 connected together then you have made an oscillator, not a timer.
    Why do you use two transistors for the relay coil when the datasheet of a 555 says it can produce up to 200mA?

    The datasheet for a 555 timer shows that with your 100k resistor and 1uF timing capacitor then the timing duration will be only 0.1 second, not for a long duration.

    Make it like this:
     

    Attached Files:

  4. BobK

    BobK

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    1,685
    Jan 5, 2010
    I have had a bat in the bedroom on two occasions in my house. Quite frightening when you wake up in the middle of the night to discover a bat flying around the room! Actually the lovely wife Morticia was awakened first, and woke me up. I think she attracts them.

    Bob
     
  5. JVH

    JVH

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    Oct 14, 2019
    Thanks for the reply . I am worried that keeping the relay coil energized for a long period might over tax a small transistor .
    OK now I have the 1k value I will try cutting out the BD140 .
     
  6. JVH

    JVH

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    Oct 14, 2019
    Thanks for the reply . I was not aware this was any kind of timing circuit it stated toggle switch . I don't want anykind of timed switch just on and off when required . Have I got the wrong 555 circuit ? I don't want to switch the full 4 amp current from a 12 meter line . The 12 meter switch line should give clues to the fact it's outside and I want it switched " from " the bedroom . I will try it with just the 555 that may cut out some issues . I said I was new to electronics like I started last week . So cut me some slack please .
     
    Last edited: Oct 14, 2019
  7. Audioguru

    Audioguru

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    Sep 24, 2016
    You said that the relay contacts are NC which is Normally Closed. Then they conduct when the circuit and pushbutton are not used. You also said that you want the relay contacts to stay open for long periods. Then the pushbutton activates the 555 timer circuit which opens the relay contacts for a long timing period.

    But now you say that you want to simply switch the relay on and off so why not just use the relay with the pushbutton switch connected to it and to the 12V through 12 meters of wires?? 12 meters is a very short distance for only 45mA of current. Almost any wire size will be fine.
     
  8. JVH

    JVH

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    0
    Oct 14, 2019
    I though opening and closing the relay is switching it on and off . I can see that this forum is one where new members get put down for their lack of knowledge so my first thread is my last .
     
  9. duke37

    duke37

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    Jan 9, 2011
    I am sorry if you are upset, there is no intention to put you down. It is quite normal to examine a circuit and simplyfy it. In your case an active circuit is not needed at all, this was spotted when the operating conditions were known fully.
    I have some kmowledge of simple electronic circuits but I appreciate any help with computers as this is where my ignorance is maximum. We can't know everythig.
     
  10. Audioguru

    Audioguru

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    Sep 24, 2016
    JVH, your first thread did not explain clearly what you want to do. Your schematic shows a 555 timer, a pushbutton and a NC relay. You said you need the relay contacts to stay open for long periods. Then if the 555 timer was wired correctly as a timer like I showed, the Bat Repeller would be turned off for a timed duration whenever you pushed the button. I did not ask why you did not leave the repeller turned on all the time.

    You did not say and did not use an on-off toggle switch, instead you show a pushbutton that is usually momentary. It activates a 555 timer.
    The 555 timer output current of 200mA is more than 4 times than what the relay coil uses so the transistors are not needed.
    But you also do not need the 555 timer.

    Your circuit does not need to use electronics, instead it is a simple on-off electric circuit. We talk about complicated electronic circuits here, not simple on-off electric circuits.

    I am sorry that I joked about your bats.
     
  11. duke37

    duke37

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    Jan 9, 2011
    I have been told that I have bats in my belfry:).
     
  12. Audioguru

    Audioguru

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    Sep 24, 2016
    There is no church with a steeple where I live but I frequently see bats flying at dusk in a nearby park. Maybe they live in a hollow tree trunk.
     
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