Timing circuit and a relay controlled by a transistor switch

Discussion in 'General Electronics Chat' started by Geir, Jul 28, 2008.

  1. Geir

    Thread Starter New Member

    Jul 28, 2008
    Hi all.
    I just joined to hopefully get some help and ideas. I'm pretty new to electronics, and have no formel training or education. Just like to have some fun building simple robot bugs, etc.. :p

    My question:
    Using a normal transistor switch (like the one from a bit down this page:
    [​IMG] http://www.kpsec.freeuk.com/trancirc.htm), can I get the relay to stay on for say 10sec, then "halt". It was easy when I used a PICmicro controlling the base, but I'd like to use as "simple" a design as usual. Hopefully using only transistors/caps/res's, but I guess a 555 timer is a viable solution..

    PS! The relay is this one:

    Sorry for what is probably an insanely stupid/easy question, but I've been searching and trying, but still nowhere closer to an answer.

  2. thingmaker3

    Retired Moderator

    May 16, 2005
    Something roughly akin to this should work:
    You'll need to experiment with the capacitor and resistor values to get the combination which drops your relay when you want it. If you know the relay drop-out current, you can calculate the values and save some time.
  3. Geir

    Thread Starter New Member

    Jul 28, 2008
    Thank you thingmaker3.
    I'll have a go at experimenting when I get home from work tonight.
    No clue as to what the drop-out current is, so I'll have some fun tinkering with it :).