10 Minute Night Light

Discussion in 'The Projects Forum' started by Tonydotholm, Jan 11, 2009.

  1. Tonydotholm

    Thread Starter New Member

    Jan 9, 2009
    1
    0
    I want a battery powered night light. Have found circuit diagrams for a couple circuits.

    What I don't have is a way to switch Vcc off from entire circuit when 10 minute time is up (output goes low).

    The circuit I like so far is one in which a switch applies Vcc to the circuit and a capacitor on pin 2 keeps trigger low so 555 fires. I just need a way to use a momentary push button switch to start Vcc flowing but have Vcc cut off when timer is done.

    I don't want circuit using battery power for the 23 hours and 50 minutes the device is not in use.

    I was thinking of using a switching transistor (2N2222 NPN) tied to output of 555. When push button is pressed, +Vcc is applied to base of NPN and output of 555. 555 fires and output is high keeping transistor conducting. Once output goes low, transistor cuts off and Vcc no longer flows through transistor.

    Any ideas?
     
  2. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,536
    First of all, go with a CMOS 555.

    There might be other good ways to do this, such as power down the entire circuit (including the 555) when the 555 goes low.
     
  3. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    I know a better wayto switch it. But you need an extra component in your circuit. A relay. i had the same problem when I made a water pump timer using 555. I didnt want that thing to run 24hrs after switching the pump off after 5 mts. It might even start the pump automatically after a power failure.

    Wire the output from 555 to drive the relay using BC547 (or any driver) and take the output from the relay contacts at N/O to be in series with the 555 Vcc supply. You will need a micro switch across the relay N/O to activate the circuit. I didn't understand your particular application so Im telling from what I understood. Give it a try.
     
  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007
    2,574
    230
    Combining yours, Bill's and jj_alukkas's ideas:

    Ken
     
  5. Wendy

    Moderator

    Mar 24, 2008
    20,765
    2,536
    Yep, Ken, that was what I was thinking about.

    [​IMG]
     
  6. jj_alukkas

    Well-Known Member

    Jan 8, 2009
    751
    5
    Absolutely.. If you need to drive something other than from that 12v, you can also utilize the other pole of the relay..
     
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