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  1. #1
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    calculate time monostabile lm555

    let me say ive run into forums who dont want any DIY'ers in it. This is like the only site that doesnt mind helping out newbies.

    i dont know much about eletrical engineering but i am a mechanical engineer.

    ok i need help designing a circuit.

    heres what i need it to do. should be simple to you guys

    scenario:
    i need a switch that has to be closed for a set amout of time (say 1 minute) before it closes another.

    power source is ~ 30 acv

    please use simple terms, and a list of the parts i will need.
    thanks.

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    switch on delay

    Considering your level of knowledge I suggest buying a relay module with a timer.
    You apply power to it through a switch then after an adjustable delay it closes it's contacts. The contacts will stay closed until the switch is opened removing the power to the module.

    A cursory glance at at the web finds the M3DOM from Broyce Control.
    http://www.broycecontrol.com/ENGLISH/S01_ALL.HTM

    Runs on anything between 24V and 240V AC or DC.
    If I understand what you want correctly all you need is one of those and some wire to connect it up.

    http://www.broycecontrol.com/PDF/M3DOM-1-B.PDF

    Electrical distributors in your country will have somthing equivalent.


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    Re: very nice forum... need help designing circuit.

    You can use 555 timer in the monostabile configuration (see picture below).
    It can directly, or through additional transistor, control a relay, and this relay can work with 30Vac. This circuit can work with 6-15Vdc, which can be geerated of what you have available, 30Vac that is.
    This simple circuit together with a small relay can be mounted on a veroboard ..

    Calculations of R1 and C1 of the 555 timer to achieve 1min (or any other time) you can find here:
    http://home.cogeco.ca/~rpaisley4/LM555.html

    555 timers can be connected in a chain, so first triggs second, and so on ..

    Last thing: what is the current in the 30Vac installation that you want to switch?

    Regards,
    IanP


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    Re: switch on delay

    ok thanks guys... i dont yet understand what u guys are telling me but i will read those links you guys gave first, then i will get back to you guys.

    and for what the 30 acv is from... i cant tell.... its part of my invention. = )

    Added after 24 minutes:

    [quote="The contacts will stay closed until the switch is opened removing the power to the module.

    [/quote]

    i need it to only close momentarly then return to opened, like if i was to push a button...

    and is there a certain name you call this relay module with a timer?

    thanks.



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    Re: very nice forum... need help designing circuit.

    scenario:
    i need a switch that has to be closed for a set amout of time (say 1 minute) before it closes another.
    ...
    i need it to only close momentarly then return to opened, like if i was to push a button...
    So, ..., should this switch (relay) close contacts for a while, then open and wait ,then close contacts again, open, wait ...and so on?
    Or, can you describe in details what should happen over certain period of time .. should this sequence repeat?

    Regards,
    IanP



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    Re: very nice forum... need help designing circuit.

    no its not a sequence.....

    so the button has to be held closed for a set amount of time, let say 1 minute.

    after a minute has been reached it then tells the relay contacts to close momentarly and return back to open, like a spring push button.

    Then the whole circuit should be ready to do that all over again.



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  7. #7
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    Re: very nice forum... need help designing circuit.

    Attached is a circuit which is based on two 555 timers.
    The first timer, after trigger switch is pressed, generates 1 minute deley.
    Timer 2 is trigged on the falling edge of the output signal from the first timer and activates relay for ≈1s.
    If you need to change times use calculator from the previously given link ..

    Regards,
    IanP



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    very nice forum... need help designing circuit.

    > is there a certain name you call this relay module with a timer?

    They are just called "timers" or "timer relays".

    You can do what you want with two of them. One for the delay before turn on, another in "stay closed for a set time" mode.

    Switchs and relays have contact bounce. When the contacts are physically pushed together they oten bounce apart again. When first pressed or energised they go on-off-on-off for a millisecond. If it is controlling a motor,a light or a heater it's not a problem. Sometimes it is a problem when control other electronics.



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