1. We will be in Read Only mode (no new threads, replies, registration) starting at 9:00 EDT for a number of hours as we migrate the forums to upgraded software.

Slow Discharging....

Discussion in 'General Electronics Chat' started by TheDag, Jun 8, 2012.

  1. TheDag

    Thread Starter Member

    Jan 1, 2010
    This circuit is automatically switching "ON" Bluetooth Device when connecting 12v to this circuit.....
    But, The discharge of the 555 is pretty slow...
    When im quickly power off the 12v and connect it again, The capacitor of the 555 is still charged and its not working(the 555)...
    I Need it to really quick discharging......
    Please help...
  2. #12


    Nov 30, 2010
  3. chuckey

    Well-Known Member

    Jun 4, 2007
    If you connect a diode from the top end of C4 to the Vcc line (cathode to Vcc). When the Vcc goes to 0v, this new diode conducts and pulls the voltage down on C4. When Vcc is restored the diode is reversed biassed and can be ignored.
  4. TheDag

    Thread Starter Member

    Jan 1, 2010
    C4 is already have diode...
    And I Just checked the input capacitor, and he is the problematic capacitor, slow discharging (C1)...
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
    If you don't mind wasting some power, put a low-value power resistor from the battery connector to ground. 100 ohms, 5W would discharge the cap in about 50 milliseconds.
    If you don't want to waste power and generate heat, attached is a way that should work. The only comparator I could find that would work is a surface mount device.
    In either case, be sure to add the diodes across the voltage regulators to protect them from reverse voltage.
  6. electronis whiz

    Well-Known Member

    Jul 29, 2010
    i can think of a few ways not sure if any will help. use a smaller capacitor, shunt the cap with a resistor, or put a potintiometer in series with the cap when the desired frequincy is reached mesuere the potintiometer and add a resistor of that value. i made a multibrator from a modified kit desing put a VR in with a cap to control the frequincey of output taped the outputs at 4 places each hooked to an led and the 4 leds flash difeentley.