Delay lamp circuit using bidirectional thyristor (1)

It is a simple delay lamp controlled by a bidirectional thyristor. Normally, the bidirectional thyristor VTH is turned off and
the light E does not light up. When you need to turn on the light, just
press SB. At this time, E is energized and emits light. At the same
time, the capacitor (1. is quickly filled with charge. Due
to the action of R., the complex tube composed of VT1 and VT2
is turned on, and C. is charged. Release SB.
After that, c^ stores the charge through R.
and discharges it to VT3, turning on VT3, which can
turn on the thyristor VTH, so the lamp F
continues to light up. When the charge of C. is basically discharged, VT3 is cut off, VTH is turned off, and the lamp E Off.
    The circuit delay time is not only related to the values ​​​​of i and C., G, R., but also related to the length of the key press. VTH
can be MAr94A4, MAC 97/16 and other bidirectional thyristors , and the port values ​​​​of VTl-VT2 should be greater than 200 .