With the improvement of people's living standard, the demand of consumers is constantly changing. The emergence of greenhouse cultivation is proof that consumers are increasingly critical of "Food is the paramount necessity of the people". Greenhouse cultivation not only allows consumers to eat anti-seasonal fruits and vegetables anytime, anywhere, but also its wide range of implementation, conducive to high-quality cultivation of fruits and vegetables. In greenhouses, too high or too low temperature will affect the normal growth of fruits and vegetables. In order to ensure that the greenhouse temperature is appropriate, the greenhouse will use high-reliability NTC thermistor to make agricultural temperature detector for temperature monitoring and temperature controlling, to ensure the high yield and high quality of fruits and vegetables.

Greenhouse cultivation temperature detector, using thermistor to replace the photosensitive element, temperature sensor including NTC thermistor is responsible for environmental temperature sampling. The temperature signal is processed by the integrated circuit. When the ambient temperature rises or falls, the temperature changes of "high, medium and low" in the greenhouse are reflected by three different color LED light emitting diodes in time. At the same time, a buzzer alarm sound is provided to alert when the temperature reaches the early warning value. The circuit of greenhouse cultivation temperature detector has the characteristics of simple structure, less components, reliable circuit performance, low production and development cost, easy to use, easy to popularize and so on.

Greenhouse cultivation temperature detector is composed of photo-metric integrated circuit, NTC thermistor, silicon switching diode, two resistors and potentiometer. The second pin of the photo-metric integrated circuit is connected with one end of the NTC thermistor; The seventh pin of photo-metric integrated circuit is connected with the positive pole of silicon switching diode; The other end of the NTC thermistor and the negative pole of the silicon switching diode is grounded; The fourth pin of photo-metric integrated circuit is connected with one end of the first resistor, the other end of the first resistor is connected with the fifth pin the of photo-metric integrated circuit and one end of the second resistor, the other end of the second resistor is grounded; The first pin of the photo-metric integrated circuit is connected with one end of the potentiometer, and the other end of the potentiometer and its movable arm are connected with the positive pole of the 6V DC power supply of the fourteenth pin of the photo-metric integrated circuit.

In the greenhouse cultivation temperature detector, NTC thermistor is used to monitor the ambient temperature, its resistance value decreases with the increase of temperature, and the second pin voltage of photo-metric integrated circuit changes with the change of the resistance value of thermistor. Potentiometer is used to set monitoring temperature, when the environment temperature is suitable, the voltage of second pin of the photo-metric integrated circuit is between high level and low level, the twelfth pin outputs low level, the tenth pin and eleventh pin output high level, so that the second LED emitting diode lights, the first and third LED emitting diodes does not light, the buzzer in the sound alarm circuit does not sound. When the ambient temperature is low, the resistance value of the NTC thermistor increases, so that the voltage of the second pin of the photo-metric integrated circuit increases, when the second pin and the fifth pin become high level, the eleventh pin and the twelfth pin output low level, so that the first and second LED emitting diodes light up, and the buzzer will sound the alarm. When the ambient temperature is high, the resistance value of the NTC thermistor decreases accordingly, so that the voltage of the second pin of the photo-metric integrated circuit drops, the second pin and the fourth pin become low level, the tenth and twelfth pin output low level, so that the second and third LED emitting diodes light up, the buzzer will sound the alarm.