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Adjustable timer circuit

Discussion in 'General Electronics Discussion' started by Tommy8389, Mar 21, 2017.

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  1. Tommy8389


    Mar 18, 2017
    Can someone help me check whether this circuit will work? :) if yes,i will be build this project within this week adjustable-timer-using-4017.jpg
  2. duke37


    Jan 9, 2011
    You do not say what it is supposed to do.

    A quick glance finds that there is no protection diode across the relay coil. This could pop off the BC547.
    You should not have the circuit ground connected to the mains ground. In the UK, the mains comes in as line and neutral and there is a separate earth.
    Harald Kapp likes this.
  3. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    A few notes:

    The circuit will do something. Whether it 'works' depends on the intended operation. You should explain what you expect the circuit to do, then we can compare this with our understanding of the circuit's operation.
    1. Add a fuse in the mains power circuit. Make sure the relay is suitable for mains operation and that it can make, carry and break the expected mains currents. Note that the inrush current (relay make operation) of a tungsten lamp is a multiple of the steady state current.
      When building this circuit, observe proper safety (isolation from mains) and possibly applicable local regulations!
    2. Reset of the 4017 is high active. If your switch SW is intended to reset the circuit, swap SW <> R2.
    3. You'll need to add a flyback diode across the relay coil.
    4. Add a 100 nF capacitor from 6 V to 0 V across each IC (555, 4017) as near as possible to the power supply pins.
    5. Last not least your circuit diagram is very unconventional. This one is readable, but you'll run into trouble with larger diagrams of that kind. See here for a tutorial.
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Definitely not. the 6 V circuit should be completely isolated from the mains circuit.
  5. Herschel Peeler

    Herschel Peeler

    Feb 21, 2016
    Re: Reset
    When the switch is on the Reset line goes low and it all works as intended. The relay clicks on and off three times in a cycle. The pin out of the transistor is a question. EBC or CBE?
  6. Audioguru


    Sep 24, 2016
    You should add a 1k resistor in series with the pot to prevent burning out the transistor at pin 7 if the pot is turned down to zero.

    I think your hard to see sketch shows it backwards. It is clearly shown on its datasheet.

    Attached Files:

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