Homemade humidity detection alarm ----- humidity detector

Keywords: humidity detection circuit diagram Author: Mo Zhendong Circuit composition The circuit is simple and easy, as shown in Figure 1, consisting of a sampling circuit, a phase amplifier, a voltage comparator, alarm indication circuit, and a power source indication. R2 and the wet-sensitive resistor RP (self-made) constitute a humidity detection sampling circuit, U1A, R3, R4 composition of the same phase amplifier, u1b, R5, R6, R7, W1 constitutive voltage comparator. R8, R9, Q1, buzzer, LED2 composition alarm indication circuit, LED1, R1 is the power supply indication, VCC supplies 3V power supplies from 2 5th batteries. working principle The LM324 is connected to a single power supply mode, and the wet-sensitive resistor RP converts the humidity to the 3 pin of the electrical signal to the U1 to perform 1001 times, the amplified signal is outputted by the 1 pin of the U1 to feed the U1 5 foot for voltage. compare. The 7 pin output alarm signal of U1 is pushed by Q1. When the 5 foot potential of U1 is higher than 6 feet, the 7 foot outputs high, Q1 is turned on, the buzzer sound alarm, the LED2 alarm indication; otherwise the 7 pin outputs low, no alarm. The value of adjusting W1 can be adjusted 6 foot potential, that is, adjust the humidity alarm threshold. The PCB board is shown in FIG. 2, and the element position map is shown in Figure 3. The fabrication of the wet-sensitive resistor Rp etched two tight tone and type fine copper wires, and the two poles 1, 2 (as shown in Figure 4), the two-pole resistance varies with the humidity, which can meet the qualitative The needs of the analysis are simple and cost-effective. The author used the circuit as the humidity alarm of the warehouse, used for two years, and the cost is around 3 yuan. Make the circuit slightly modified to provide input for the digital humidity indicator, providing a start signal for the automatic dehumidifier, and the like.

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