This unit can be used in any 12V powered continuous alarm device to make it intermittent. It can also be used to control any 12V powered signal light to make it flash intermittently. The general alarm scale is mostly variable or intermittent.
The circuit diagram of this unit is shown below. In fact, the working principle and circuit structure of the device are the same as those of the above-mentioned FIG. 7, and two NAND gates in the 4011 integrated circuit are used as the ultra-low frequency oscillator, and the other two NAND gates are connected in parallel for the buffer shaping stage; The 2N2222 crystal triode is used as an output amplification tube, and the controlled siren or bulb is controlled by its collector current. If the current of the controlled siren is greater than 1A, the collector current of 2N2222 is small and cannot be driven. Then, a breaker is connected to drive, and the breaker contacts are connected in series to the power circuit of the controlled object. The intermittent pause time is determined by the product of R1 and C1 in the figure, as shown in the figure, with an intermittent time of about 3 seconds. Capacitor C1 should not be used for electrolysis. Both paper and polyester film can be used. If there is no such large capacity capacitor on hand, you can use 0.1μF capacitors that are easy to purchase in parallel.
If you want to change the interval time, you can change the value of C1 or R1. The value is large and the interval time is long; the value is small and the interval time is short.
The diode in parallel with the breaker or guard is a freewheeling diode to protect the 2N2222 tube from breakdown by the reverse high voltage generated by the inductive load. If the controlled load is a resistive load, such as a light bulb, the diode can be disconnected. The diode can be any rectifier diode with a withstand voltage of 50V or more and a current greater than 1A. 
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