Over-temperature and cooling alarm circuit

Over-temperature and cooling alarm This is an over-temperature and cooling alarm composed of CD4011 four NAND gate integrated circuit, which is used to monitor the temperature of the thermostatic box. When the thermostatic circuit fails or there is a power outage, and the temperature inside the box is higher or lower than the allowed range, it can sound an alarm to remind people to take corresponding measures. This circuit has a resolution of 0.1°C. working principle　　　 　　　　　　　　　

See Figure 1 for the circuit. Diodes VD1 and VD2 are both placed in a thermostatic box. When the temperature in the box is lower than the lower limit, the potential of point a in the figure is greater than the threshold voltage U of the input terminal of gate A, and the output terminal of gate A is low level, causing the output of gate B to be high. level, then the multivibrator composed of gate C and gate D starts to oscillate, and the piezoelectric sheet emits an alarm sound; when the temperature in the box is higher than the upper limit, the potential at point b is less than the gate B threshold voltage U, or it can Make door B output a high level, and the piezoelectric sheet YD will sound an alarm. Only when the temperature inside the box is between the upper and lower limits, the YD will not make any sound. Adjust the values ​​of RP1 and RP2 respectively to change the lower limit and upper limit values ​​respectively. The power circuit is an AC and DC power supply, and E is a backup power supply. When the AC power supply fails, VD3 is turned on, and the backup power supply supplies power to the circuit. Since this circuit consumes very little power, stacked batteries can be used as the backup power supply to reduce the size. The component selection and production component list is shown in the table below. No. Name Model Quantity R1, 2 Resistor 1K 2 R3, 4 Resistor 120K 2 R5 Resistor 3K 1 R6 Resistor 680Ω 1 RP1, 2 Potentiometer 470K Linear 2 C1, 2 Polyester capacitor 0.22u 2 C3 Polyester capacitor 1700P 1 C4 Electrolytic capacitor 200u 1 C5 Electrolytic capacitor 470u 1 VD1, 2 Detection diode 2AP9 2 VD3, 5 Rectifier diode IN4001 2 VD4 Zener diode 2CW55 6V 1 IC Four NAND gate integrated circuit CD4011 1 YD Piezoelectric buzzer HTD-27A or HTD-35A 1 T Power transformer 12V 2-5W 1 E Battery pack 6V 1 When the wires connected to the sensors VD1 and VD2 are too long, it is best to use shielded wires to enhance the anti-interference ability. Finally, take the chick incubation temperature monitoring as an example to illustrate the adjustment method: first stabilize the temperature of the incubator at 36.5°C, move the sliding arm of RP2 to the lowest end, and then adjust the lower limit adjustment potentiometer RP1 to YD Then adjust the incubator temperature to 39.5°C and adjust the upper limit adjustment potentiometer RP2 to the critical point where YD makes a sound or not. In this way, when the temperature of the incubator is lower than 36.5°C or higher than 39.5°C, an alarm will sound and the oscillator can be officially used.