Laptop photoelectric detection circuit

This is the electrical schematic diagram of the photoelectric detection of each laminating machine
. It consists of a set of bistable flip-flops
and detection signal input circuits.
    Under normal circumstances when there is no bad book signal, we
make the left tube VT1 of the flip-flop cut off and the right tube
VTZ conduct. When the detection time switch S (instantaneously closed) operates, the detection photoelectric tube VP also sees light conduction. -6V will be added
to the base of VT2 through VP, causing the flip-flop to flip (VT1 is on, VT2 is off) and the neon lamp L is on. If the time switch S operates,
the light of the photoelectric tube VP is avoided (cut off) by the paper. -6V cannot reach the base of VT2.
    When the time switch S is in the off state, +12V in the circuit will be added to point B through the lZk resistor and VD1 diode to
reverse bias the VDB diode to prevent interference.
    When the hinging machine is in normal condition, when the time switch S is activated, the light of the photoelectric tube VP is blocked. If the hinging machine is not closed, the photoelectric
tube VP is illuminated and turned on.