Multipurpose pocket two-way alarm circuit

Multipurpose pocket two-way alarm This is an alarm circuit that can be set in both directions. It uses a Schmidt integrated circuit with sensitive response and sound and light display. It is small in size and has low power consumption. There are only 13 components in total and the cost is very low. Working principle: 　　　　　　　　　　　This circuit is divided into two parts, consisting of A, B, R4, and C1 to form the upper limit alarm function. C, D, R5, and C2 constitute the lower limit alarm function. The circuit is shown in Figure 1. Normally, RP1 and RP2 set two alarm points, the upper limit and the lower limit respectively, so that the A and C input terminals are both high level and the output is low level, causing the oscillators to stop oscillating. When the temperature is too high, the resistance of the thermistor R1 decreases, causing A to output a high level, B to vibrate, and the piezoelectric ceramic piece YD to emit a high-pitched buzzer. At the same time, the light-emitting diode LED1 lights up, indicating that the temperature is too high. When the temperature is too low, the resistance of the thermistor R2 increases so that C outputs a high level, D starts to vibrate, and the piezoelectric sheet YD emits a low-pitched buzzer. The light-emitting diode LED2 lights up, indicating that the temperature is too low. Since the static power consumption of the CMOS circuit is extremely small and the current is only at the microampere level, the power consumption in the static state is mainly on RP1, RP2 and the thermistor. If a special temperature measuring resistor with a resistance of more than 100 kΩ can be used, and RP1 and RP2 are increased accordingly according to the proportion in the figure, the power consumption in static state can be controlled to be very small, which is extremely beneficial to extending the service life of the battery. See the table below for component selection and production component list. No. Name Model Quantity R1, 2 Thermistor 1K 2 R3 Resistor 3K 1 R4, 5 Resistor 2M 2 RP1, 2 Adjustable resistor 10K Linear 2 C1 Polyester capacitor 300P 1 C2 Polyester capacitor 1000P 1 LED1, 2 Light emitting diode Φ3mm 1 IC Shi Mitech integrated circuit CD4093 or MC14093 1 YD piezoelectric buzzer Φ20mm HTD20A-1 type 1 E battery lighter special 12V small battery 1 The components used in this alarm are not large, and can be made as compact as a matchbox. If a photoresistor is used instead of a thermistor, it can be used as a light intensity alarm. You can also use the other input end of the Schmitt trigger to create a dual-function bidirectional alarm for light and temperature. The control signal is derived from the LED to control light filling and humidification (such as ultrasonic humidifier) ​​to form an automatic light filling and constant humidity controller.