Driving a monostable relay with a single button

Discussion in 'The Projects Forum' started by andreapg, Feb 18, 2010.

  1. andreapg

    Thread Starter Active Member

    Feb 2, 2010
    I created this project with educational intent (was my first schematic using active components).
    This simple circuit can be utilized to drive a monostable relay through a single button switch.
    At the start condition the relay does not work. When I press the button (P) T1 transistor is energized
    through R1 and R2, and the capacitor charges. The coil is jumped by the button. So, once i release
    the button, the coil is energized. T1 keeps the high level through the capacitor and the relay
    switch (10-6).
    When I press the button again T2 is energized (the relay switch is now closed between 9 and 5).
    The current which flows through T2 collector let T1 switch off.
    When I release the button T2 switches off. T1 would switch on 0.01 seconds after (once the
    capacitor would be partially charged).
    But the coil turns off within 0.003 seconds only. Than the circuit takes the start condition.