Two-way touch switch (2)

Diodes VD1 ~ VD5 and capacitor C3 form a simple capacitor step-down bridge rectifier and voltage stabilizing circuit, which outputs about 12V DC
voltage for the entire switch. Normally, transistors VTI ~ VT3 are in cut-off state, relay K does not operate, its normally open
contact is open, and various electrical appliances controlled by it do not work. When you need to close the switch , you only need to touch the electrode piece Ml. The human body leakage
current is injected into the base of the transistor VT2 through the resistor Rl and is amplified by VT2 and VT3. The VT3 is saturated and conductive, and
the relay K obtains the electric suction platform, which is normally open. The contact kl is closed, so that the base of VT2 is connected to the positive power supply through the resistor R3, so that
the circuit is in a self-locking state. Even after the human hand leaves Ml, VT2 and VT3 can still maintain the conductive state. The other normally open contact
k-2 of K is closed, which can control the energization of lights or other electrical appliances.
    When you need to shut down, just touch the electrode sheet M2, and the human body leakage current is injected into the base of VT1 through the resistor
R2, causing VT1 to quickly flip from the off state to the on state, and its collector, the base of VT2, suddenly changes to a low level, Vr2 And VT3 immediately
flips from the on-state to the off-state + the relay K is released when it loses power, its normally open contacts kl and k-2 jump open, the self-locking is released, and the controlled electrical appliance
is also closed due to the loss of power.