Variable Timer 3-15 minutes

Discussion in 'The Projects Forum' started by monkeyman3, Sep 25, 2009.

  1. monkeyman3

    Thread Starter New Member

    Sep 25, 2009

    I found your forum after searching on Google, but haven't found any threads on what I'm after.

    I basically need to trigger a relay to switch over between 3 and 15 minutes, possibly 3,4,5,8,12,15 minutes, but variable is fine if I can calibrate it with a watch. It doesn't have to be down to the second.

    I know which is the hot end of a soldering iron, but apart from assembly my electronics theory is pretty poor.

    It was suggested to try a 555 circuit but with a huge capacitor, although this would mean swapping components to change the interval.

    Would it be quite easy to get a battery powered circuit with relay to fit in a project box?

    thanks for any advice or places to search / buy
  2. mik3

    Senior Member

    Feb 4, 2008
    If you want these standard delays you mentioned you can put the appropriate resistors in the circuit and use a rotary switch to choose each resistor accordingly.
  3. KMoffett

    AAC Fanatic!

    Dec 19, 2007
  4. Wendy


    Mar 24, 2008
    There are several ways to do this. Is there any significance to the times you've selected? Also, how repeatable long term does it have to be, is a drift of 15 seconds for a 15 minute time unacceptable? I'm picking an extreme case to get a feel for what you want.

    There is a chip called a 4060, it includes a built in RC timer and 14 stage ripple counter (14 flip flops in sequence). Add some simple logic (probably extremely simple given your requirements) and you have what you're after.

    So what do you want it to do when it is finished timing, sound an audible alarm and light an LED?

    BTW, kitchen timers are a good buy nowdays, and give a much nicer feedback in the form of a count down.
  5. mkbutan

    AAC Fanatic!

    Sep 30, 2008
    yes mr. bill is right you should use the ic cd-4060 that's the best long time back i made this timer for our crome plating machine unite's on time f-00 to 20/off time f-00 to 05/on mint's.
    Last edited: Oct 5, 2009
  6. monkeyman3

    Thread Starter New Member

    Sep 25, 2009
    Thanks for all your replies, it will just be used for some low voltage lights, and the timing doesn't need to be 100% accurate, just to save me using a countdown timer.

    That Yahoo site is about my level of building :D

  7. bountyhunter

    Well-Known Member

    Sep 7, 2009
    Use a 555 timer with good quality caps like tantalum or poly types.
  8. Bernard


    Aug 7, 2008
    How do you start timing? Are mechanical switches for selecting times OK?; or how do you wish to select? I like the 4060, for some things; no outpots for stages 1,2,3,11, & needs a flip-flop if used as a oneshot to start & stop. ?just one " lamp" or group of lamps on one driver? Lamp load? 555 looking better.