High and low temperature two-way thermometer circuit diagram

High and low temperature two-way thermometer circuit diagram

The picture shows the circuit diagram of a high and low temperature two-way thermometer. The 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.

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 to stop the oscillators. 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.

If a photoresistor is used instead of a thermistor, it can be used as a light intensity alarm. The other input end of the Schmitt trigger can also be used for dual-function bidirectional alarm of 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.

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.