DIY dew point detector ----- ua741 defin-point hygrometer

The dew point detector has been widely used in sensitive electronic devices, such as digital cameras and copiers, etc., which are used to protect these devices from moisture, resulting in failure. The official commercially available dew point detector is priced, so as long as it can get the dew point sensing component, you can do it yourself. Alternatively, a small dew point sensing element in a waste recorder or a video camera can also be utilized. This simple, highly sensitive anti-galaxy circuit can also be used to prevent the surface of the home, such as tap water pipes and glass windows, and more. The working principle of the dew point detecting element DS1 is to respond according to the change in resistance of the conductive polymer in the film on the ceramic matrix. If the polymer is wetted due to conjunction, the resistance is greatly increased because the distance between the internal conductive resistance points is long after expansion of the polymer. Be Be In the circuit shown in the drawings, the dew point detecting element DS1 is connected to the inverting foot 2 of the op amp UA741 (ICl), and the same phase is provided with the reference voltage with R2, VR, and R3. If the humidity is high, the output state of the ICL is immediately changed, and the optical coupling drive transistor TL is turned on, and the optical coupling IC2 is turned on. The VR1 is adjusted so that the IC2 is turned off in the case where the DS1 detects low humidity, and in the case of high humidity. Circuit operating voltage is DC + 12V, which can use AC adapters. If the component is selected correctly, the supply voltage can also be reduced. The circuit can be installed on a normal PCB board and placed in an appropriate aluminum cartridge. The dew point detection element DS1 is fixed with double-sided adhesive on the front panel. For the bond firm, it is best to clean and dry before the surface of the aluminum cassette, it is recommended to use isopropyl alcohol as a detergent. To extend the working distance, connect the dew point detection element DS1 to the circuit with a pair of long lines. If you use a shielded cable, you can eliminate transient problems. The dew point detecting element can accurately measure the dew point and activate the external connection relay or similar controller to make a sound alert. The comparator circuit increases a small amount of late effect to avoid the unstable detection information. There is also a security chip 4N35 (IC2) in the circuit, and the internal photoelectric transistor is suspended, so it can be done with any simulation, digital devices, only need to be modified slightly in the rear trigger input. For simplicity, the optical coupling IC2 can be replaced with one electromagnetic relay. Instead, R6, C2, and IC2 were removed, and the relay was connected between the transistor TL emitter and ground. Do not forget the diode on both ends of the relay coil when using the relay.