Design of siren intermittent switch

Design of siren intermittent switch

This device can be used for any 12V powered continuous alarm device to make it work intermittently. It can also be used to control any 12V powered signal light to make it flash intermittently. Most general alarms are modulated or intermittent.
The circuit diagram of this device is shown in the figure below. In fact, the working principle and circuit structure of this device are the same as those of the circuit in Figure 7 above. It also uses two NAND gates in the 4011 integrated circuit as ultra-low frequency oscillators, and the other two NAND gates are connected in parallel as buffer shaping stages; 2N2222 crystal triodes are used as output amplifiers, and the controlled siren or light 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 circuit breaker must be connected to drive it, and the circuit breaker contacts are connected in series to the power supply circuit of the controlled object. The intermittent intermittent time is determined by the product of R1 and C1 in the figure. As shown in the figure, the intermittent time is about 3 seconds. Capacitor C1 should not be electrolytic, paper or polyester film can be used. If you don't have such a large-capacity capacitor on hand, you can use a 0.1μF capacitor that is easily available on the market in parallel.
If you want to change the intermittent time, you can change the value of C1 or R1. The larger the value, the longer the intermittent time; the smaller the value, the shorter the intermittent time.
The diode connected in parallel with the circuit breaker or alarm is a freewheeling diode, which is used to protect the 2N2222 tube from being broken down by the reverse high voltage generated by the inductive load. If the load being controlled is a resistive load, such as a light bulb, this diode can be disconnected. The diode can be any rectifier diode with a withstand voltage of more than 50V and a current greater than 1A.