Touch switch circuit

Shown is a touch switch circuit . When the metal plate M is touched by hand, the charge on CI will be added to the input terminal of
NAND gate 2 through the human body resistance, causing it to become a high level. Eventually, NAND gates 3 and 4 will output a high level, causing VT1, VT2 is turned on, relay Kl
absorbs the stage, and its contact Kl-l is closed, which can control the load operation. Since NAND gate 1 and NAND gate 2 are connected through resistor Rz,
the high level provided by cl to the input of NAND gate 2 will remain. Even if the hand leaves M, the circuit will remain in this state until until M is
touched again.
    When the relay maintains the suction stage state, the input terminal of NAND gate 1 is low level, c] will be discharged to about ov through Ri and NAND gate l.
    When M is touched again. C. The ov voltage is added to the input end of NAND gate 2 through the human body resistance . The circuit returns to its original
state, that is, rri and VT2 are cut off and relay Kl is released. K1.1 contact is open.