Use NE555 to make a touch self-extinguishing table lamp

The touch self-extinguishing desk lamp circuit made with NE555 is shown in Figure 3-8. The left part of the dotted line in the figure is the original circuit of the desk lamp, and the right
part is the newly added touch self-extinguishing control part.
    SB is the original switch of the desk lamp. When the switch SB is closed, the desk lamp H lights up. At this time, the self-extinguishing control circuit does not work.
Turn on the switch SB, and the desk lamp H goes out. At this time, the desk lamp has a touch self-extinguishing function. The working process of the circuit is: time base circuit A
is connected into a typical monostable trigger, and its transient time is determined by R2 and 03. C1, C2 and VD1, VD2 form a simple
capacitor step-down half-wave rectification and voltage stabilizing circuit. Both ends of C2 can provide a DC voltage of about 12V for the time base circuit A. When the time
base circuit is in a stable state, its pin 3 outputs low level, the triac VS is in the off state because there is no trigger voltage, and
the light H does not light up. When a human hand touches the touch electrode sheet M, the human body induced clutter signal is sent to the trigger
terminal 2 of the time base circuit through R4. The negative half cycle of the signal causes the time base circuit A to trigger and flip into a transient setting, and the output of pin 3 is high. level, vs
obtains the positive trigger voltage through resistor R3 and turns on, and the lamp H lights up. At this time, the internal discharge tube of the time base circuit is cut off and pin 7 is left floating
, so the 12V positive power supply can charge the capacitor C3 through the resistor R2, causing the voltage at both ends of C3 to continue to rise. When it rises to 2/3 VDD
, the transient ends and the circuit Turn back to steady state reset, pin 3 outputs low level, vs loses trigger current, when the alternating current crosses zero
, it turns off and the light H goes out. At this time, the internal discharge tube of the time base circuit is turned on, so pin 7 is grounded, and the charge stored in C3
is discharged to the ground through pin 7. At the same time, it is blocked by pin 7 and cannot be recharged unless the electrode sheet M is touched again.
    The transient time of this circuit can be estimated by the formula ~1.1 (R2×03). Because the positive error of the electrolytic capacitor is too large, it has been measured that the lamp can light up for about 150 seconds every time M
is touched .