Flashing LED for 20 seconds

Discussion in 'The Projects Forum' started by micro kev, Feb 15, 2011.

  1. micro kev

    Thread Starter New Member

    Feb 10, 2011
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    Hi, I'm having problems with this circuit i found on the internet. I've put it all together on a breadboard the LED just flashers all the time. The description of the diagram say flashing LED for 20 seconds when button pressed.
    I'm using the HCF40106BE which i thought was right for the job?

    Wondered if anybody could put and light of this?


    Thanks, Kev
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    The LED begins flashing when the pushbutton connects the 1uF capacitor and the 10k resistor to ground. Then the 100uF capacitor is quickly charged.
    The flashing is supposed to stop when the 100uf capacitor is discharged by the 100k resistor then the output of the 3rd inverter goes high and the second diode stops the oscillator.
     
  3. micro kev

    Thread Starter New Member

    Feb 10, 2011
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    I've got this working think it was a connection, I'm wanting to trigger this by the slightest audio level, wondered what is the best way to add this circuit?

    Also I'd like the led on low level constant and then to go off when triggered/ flashing.

    Any idea's

    Thanks, Kev
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    Research VOX (Voice Activated Switch) with Google. Once you have this circuit, flashing an LED is minor. I'd even try designing one for you, but my free time has basically evaporated, and I already have too many other irons in the fire.

    If you come up with something please post it, it isn't the first request for something like this we've seen.
     
  5. micro kev

    Thread Starter New Member

    Feb 10, 2011
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    I've got it to trigger now, but worried about power going back up the socket and frying something. Just need to work out this dim/low level LED that's on constant then go's off when circuit flashers. Do you think i could do this with the IC that's in the circuit all ready or is a transistor job..??

    i'm quite pleased with myself! I've not done no electronics since Tandy when under..

    That must be 20 years ago.
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    Tandy is alive and well last I heard. They are Radio Shack, which is what they changed their name too. What part of the world are you?

    Power going back up the socket? The circuit runs off of 6V, if you are using AC to power it it should be from a wall wart.

    Is the LED staying on continuously after it blinks?
     
  7. Audioguru

    New Member

    Dec 20, 2007
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    Radio Shack stores in my part of Canada disappeared about 15 years ago. A few stores had their name changed to: The Source by Circuit City. They still sell over-priced cell phones, kids toys, computer accessories and batteries.
     
  8. micro kev

    Thread Starter New Member

    Feb 10, 2011
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    LOl.. yes bill I'm from the uk.. Tandy shut down over here years ago, i loved going in their when i was young with its 500 in one kits.. that all i ever wanted for xmas!! & i got one.

    Not manage to get the LED on low level yet after blinking, yeah looking at the circuit it will have 6v going back up to my output socket. Not using AC running on a battery.

    What is a wall wart?
     
    Last edited: Feb 16, 2011
  9. Wendy

    Moderator

    Mar 24, 2008
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    Power supply that plugs directly into the wall, creating a bump off the outlet. How are you powering this gadget?
     
  10. micro kev

    Thread Starter New Member

    Feb 10, 2011
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    It's powered by a battery bill.
     
  11. Wendy

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  12. micro kev

    Thread Starter New Member

    Feb 10, 2011
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    It needs to be powered by a battery i need to take it mobile, the power is not the problem.
    I've got the circuit working what I'm trying to work out is lighting the LED constant on a low level/dim (standby). Until its triggered/blinking..20 seconds...back to standby low level LED.

    Thanks, kev
     
  13. micro kev

    Thread Starter New Member

    Feb 10, 2011
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    I've managed to fix what i needed i think..? pin 4- resistor 470 ohms (for now)-diode-to LED. On the original circuit after 470 ohms resistor-diode-to LED.
    LED stays on now a little bright until i get some more resistors, then go's off when flashing!!
    Back on when blinking stops!!

    Nothing smoking or getting hot!

    I'm just wondering how long the 9v battery will last ?

    Thanks again, Kev
     
    Last edited: Feb 18, 2011
  14. Audioguru

    New Member

    Dec 20, 2007
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    The original circuit has 470 ohms marked 470R feeding the LED, not 470,000 ohms which would be marked 470k ohms.

    Datasheets of 9V alkaline batteries from Energizer and from Duracell on their websites show how their voltage drops with different amounts of load current with duration.
    The battery will power one LED at 20mA for about 8 hours when the voltage has dropped to 7V.
     
  15. micro kev

    Thread Starter New Member

    Feb 10, 2011
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    Yes it is ohms sorry, I got excited with my new circuit..

    What would be the best way to make this circuit low power so the battery last longer?
     
  16. Audioguru

    New Member

    Dec 20, 2007
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    The battery will last longer if you make the LED use less current by increasing the value of the 470 ohm resistor but then it will appear dim.
     
  17. Wendy

    Moderator

    Mar 24, 2008
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    There are other ways. I've got a series of projects all using a CMOS timer that last at least a month or longer using 2X AAA batteries that flash an LED continuously.

    The 555 Projects

    Look for the long duration LED flashers in the title.

    If you want it to flash for only 20 seconds, that is easy enough to do.

    What is it for, if you don't mind me asking.
     
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