Make a flashing light with the old KD-9300

The flashing light circuit made with the old KD
-9300 doorbell chip is shown in Figure 3-37. First, the 68k Q external oscillation resistor on the chip should be soldered and left unused, leaving the two oscillation terminals OSCI and OSC2 on the chip floating.
    The 220V AC power is reduced by Rl current limiter, rectified and stabilized by VD1, VD2 and filtered by C1 to output about 3V DC voltage for
music integrated circuit A. Resistor R2 inputs a 50Hz AC signal to OSC2, an oscillation terminal of the music integrated circuit.
This AC signal can output a square wave signal of approximately 0.4Hz after being divided and counted within the integrated block, thus turning
on and off the VT gap of the orchid tube. When VT is turned off, the thyristor VS obtains the trigger current through the resistor R3 and is turned on. The lamp H is powered on
and emits light : when VT is turned on, the gate of VS is grounded by the transistor VT. VS loses the trigger current and turns off when the alternating current crosses zero. off,
the light H goes out. Therefore, the lamp H can flash and emit light at a frequency of 0.4Hz. Since when vs is turned on, the current flowing through H is half-wave
alternating current, and the bulb is in an under-voltage working state, so the flashing light has an extremely long service life.