Touch-type adjustable timing circuit (1)

It is a practical touch-type adjustable timing light circuit whose timing time can be continuously adjusted within ih.
When the timer is set, the light F will go out automatically. In addition to being used to turn off the lights at a timed time, it can also be used to
turn off other household appliances at a timed time.
    Normally, the three rescue pipes VT], VT2 and VT:~ are all in the cut-off state, the moving contact kl of the relay K
is open, and the lamp F does not light up. If a human hand touches M, the mixed signal of the human body is amplified by the field effect transistor VF
, and the well passes (1. Note the base of VT1. Since the collector of vri should carry a large value of RP, VTI is
easy to Entering the saturated conduction state, at this time, the charge stored in the (j) beam is discharged through VT1, and the resistor R; the left end
potential decreases. The PNP composite tube composed of vr2 and VT3 enters the conduction state from the cut-off state, and the relay K When
the electric power is drawn, the contact kl of the moving table is closed, and the lamp E is energized and casts a curse.
    After the hand leaves M, although VT1 quickly returns to the cut-off state, due to the capacitance (1), the voltage at both ends cannot be interrupted, and
it will cause harm to RP, R, it will take some time to charge, so the potential of the left end of R, cannot rise immediately, and the relay K can still
maintain the pull-in state. At this time, the power supply passes through RI' and R. to charge G, so that the voltage at the left end of R, continues to rise. When it rises to
a certain value, VT2 and VI3 gradually turn on and enter the cut-off state, the relay K loses power and is released, the contact k1 jumps open, and
the current RJE goes out.
    The length of the circuit timing time is mainly determined by (RP+R.) and ( The charging time constant of _¨, in addition,
the resistance value of R and the p value of VT2 and VT3 also have an impact on the timing time. Using the display data to adjust 1 and the potentiometer RP, the
timing time lb with a maximum length of ih can be obtained. If If you want to extend the timing time, increase the capacity of the capacitor (.