help: relay cutoff delay

Discussion in 'The Projects Forum' started by Alex Morfe, Nov 5, 2014.

  1. Alex Morfe

    Thread Starter New Member

    Oct 5, 2014
    19
    0
    hi guys!
    with this circuit (from http://www.casperelectronics.com/images/simpleCircuits/4017.jpg):
    [​IMG]
    (without consideration to the 555 circuit) how can I make the relay stay ON for 1 second after it is turned OFF (counter increments)? is it as simple as paralleling a capacitor to the diode? if yes, what value? input voltage is 9 volts.
    thanks!
     
  2. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,503
    380
    hi,
    If the 555 timer is set to give 1Hz, you could add a diode from pin3 to the Base and a diode from pin2 to the Base, effectively making an OR gate.
    Initially pin3 would be High and the relay energised, the first clock pulse would select pin3 High for 1 second until the next 1 HZ from the 555.

    Is this what you are asking.?
    E
    BTW: I would a 100R in series with the Base
     
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    If the 555 period is 1sec (1Hz), then you can get a 1 to 9 sec delay before the relay is energized, and then a 1 sec duration while the relay is energized before the counter moves onto the next stage and either stops (if the reset is connected), or keeps running(if the reset is grounded as shown). If the timer keeps running, you will get the initial delay of 1 to 9 sec off followed by 1 sec on, followed by 9 sec off, 1 sec on forever.
     
    Last edited: Nov 5, 2014
  4. Alex Morfe

    Thread Starter New Member

    Oct 5, 2014
    19
    0
    hi eric. hi mike.
    thanks for the replies.

    as mentioned earlier, please don't focus on the 555 section -- as i'll be using different feeds to the decade counter...
    anyways... using the above circuit, when the decade counter increments, the pin#3 goes OFF and pin#2 goes ON simultaneously. what I need is that when the pin#3 goes OFF, the relay attached to it stays ON for another 1 second -- for that 1 second, both relays on pins #3 and #2 is ON. after that 1 second the relay on #3 goes OFF while #2 stays ON (until 1 second after the next increment).

    I am hoping that it can be achieved by simply attaching a capacitor to the relay, that it will be charged while the pin is ON, then supplying the relay with enough power to stay ON for another second when the pin goes OFF. But I don't know where to attach it, what value to use, or if it's even possible. :p

    I hope I stated that clearly. :)
    BTW, I'm just an enthusiast/hobbyist/kit builder. :)

    Please help.
    Thanks.
     
  5. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
    2,503
    380
    hi,
    If you change the transistor/s to a 2N7000 FET, its possible to get delayed OFF's by using a diode/res/cap combination.

    The diode would be from pin3 to the FET Gate, the Gate would also be connected to ground via 1meg ohm and a 1uF in parallel.
    The 'charge' of the 1uF would keep the FET ON for ~1 sec.

    Repeat the above diode/res/cap FET combo for any pins you wish to delay.
    E
     
  6. Alex Morfe

    Thread Starter New Member

    Oct 5, 2014
    19
    0
    will try that as soon as I get some 2N7000s.
    thanks! :)
     
Loading...