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Looking for some assistance with a 555 one shot controller?

Discussion in 'General Electronics Discussion' started by caddyspark, Aug 21, 2018.

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  1. caddyspark


    Aug 21, 2018
    I have a oneshot controller that when i power it, there is a time delay then the LED i wired in comes on, I need it to work the opposite way, power on - LED on, then time delay and turns it off
    images below

    ive got a 12v feet to it and i need to illuminate a LED for 2 or so seconds IMG_20180821_172956.jpg IMG_20180821_173002.jpg IMG_20180821_173008.jpg IMG_20180821_173014.jpg IMG_20180821_173023.jpg

  2. kellys_eye


    Jun 25, 2010
    I presume you connect your LED via the relay contacts - if so then use the (c) common and the (nc) normally-closed contacts. Supply power to (c) from the feed to the timer and power the LED from the (nc) terminal to ground via a current limiting resistor.
  3. LESpark


    Jun 30, 2018
    Which of the 3 contacts by the relay is the normally closed one?

    I put 12v to the +ve and ground

    I then took power from the +ve and connected to one of the terminals thats shown as closed with the common (see photos)
    And the +ve to the LED from the (what I assume is) common
    And the ground from the LED back to the ground terminal

    And what happens is, when I connect power there is a short delay and the the led is perminantly lit
  4. Bluejets


    Oct 5, 2014
    Photo 3, common is centre and the right side shows a contact normally closed. That's why they call it n/c, normally ( without being activated) closed.

    Operation of the relay state is usually via jumpers although the above is a simple fix for you.

    Did you read the instructions as they are usually available either on the site where you bought it or if Ebay, other suppliers usually have details.
    To be fair they can be in Chinese English which can be difficult to follow sometimes.
    Last edited: Aug 21, 2018
  5. Alec_t


    Jul 7, 2015
    What effect does changing the jumper positions of S1 and/or S2 have?
    Bluejets likes this.
  6. Bluejets


    Oct 5, 2014
    I think Alec might have this as it is not a 555 timer but a cd4541.

    Where did you get it?
    ( link?????)
  7. ratstar


    Aug 20, 2018
    sorry for being a little off-topic, but all u need is to run your signal through a capacitor, and ull get a one shot, when it fills up itll stop conducting. If u connect the legs with a heavy resistor, youll stop, release very little current in the offmode, but when current is removed from it, itll reset ready to fire again.
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