If you
have a problem for mechanical(push on/push off
switch), electromagnetic(latching relay) and electronic(CMOS logic), this
circuit is one of the solution circuit but few(if any) good discrete electronic
solutions. Here’s the figure of the circuit;
When the pushbutton is initially closed, it
directly turns on the gate of Q1 via D2. Q1 turns on after a brief delay
determined by the charge time of C1. Q1 then biases Q2 on, and Q2 seals in the
pushbutton signal and C2 charges up to 12V via R8 and D2. When the pushbutton
is closed again, the top side of C2 is grounded via the pushbutton action
through D1. The lower side of C2 goes negative and dumps half of its charge
into C3. The negative voltage on C3 turns on Q3 that is connected in the common
collector configuration (emitter follower). The emitter of Q3 shorts the bias
voltage of Q2 to common thus turning off Q1 (as soon as the pushbutton is
released).
