[Newbie] How to change pulsing power output to constant? [HELP]

Discussion in 'The Projects Forum' started by ABaruwal, May 27, 2011.

  1. ABaruwal

    Thread Starter New Member

    Jan 28, 2011
    15
    0
    I bought a alarm clock kit for my project. I wanted to connect this kit with another circuit that I made which contained several LEDs which will light up gradually. I was thinking of powering the LED circuit from the kit's output; buzzer.
    However the issue is, When I did connect the LED circuit to the kit the LEDs started flashing due to the pulsing power output.

    Is there a way I can possibly change this pulsing output to constant and stop the LEDs from flashing?

    I know for sure that the LEDs i used aren't flashing LEDs as i have connected it separately to a PSU and the leds didnt flash.

    I don't really want to change the kit's function as it physically cannot be changed.
    I tried making a bridge rectifier circuit, but it didnt work as the power going in the kit was DC.

    Could you please suggest ways i could solve this problem?

    Click this link to see the details of the alarm clock kit that i used

    Thank you
     
  2. ABaruwal

    Thread Starter New Member

    Jan 28, 2011
    15
    0
    Any possible solutions?
     
  3. bertus

    Administrator

    Apr 5, 2008
    15,646
    2,344
    Hello,

    The flashing is programmed in the used chip.
    If you want a steady output, the program needs to be changed (wich is probably uknown).
    An other possibility is feeding the flashing signal into a retriggeble monoflop.

    Bertus
     
  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
    230
    You can use a simple missing pulse detector circuit. How fast do the LEDs flash? Slow on-off pulsing, or fast flicker like the buzzer?

    Ken
     
  5. ABaruwal

    Thread Starter New Member

    Jan 28, 2011
    15
    0
    They flash slow on off, on for 2 secs and then off for 2secs.
     
  6. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
    230
    Attached is a retriggerable monostable 555 timer circuit. Each time the buzzer output goes high, the 555 timer's output (pin 3) goes high and stays there for ~3 seconds after the buzzer goes low. Since you buzzer goes high for 2 seconds once every 4 seconds, the output will stay on. You may have to play with the values for R4 and C1. My values were just a quick estimate. The TTL version 555's output will handle 200mA max, while the CMOS version's output can handle only 100mA.

    Ken
     
    ABaruwal likes this.
  7. ABaruwal

    Thread Starter New Member

    Jan 28, 2011
    15
    0
    Thank you for the diagram and a quick response. My only question is will this circuit work for output with longer on/off delays, for e.g. on for about 5secs and off for another 5secs
     
  8. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
    230
    Yes. It's just an matter of increasing the on-time by increasing the values of R4, C1, or both. Doubling the value of R4 or C1 will approximately double the on-time. Doubling both will increase the time by ~X4.

    Ken
     
    ABaruwal likes this.
Loading...