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Turning Dehumidifier ON/OFF or other appliances or alarms automatically as humidity rises and falls can be desirable.
At top, in simulator circuit is humidity sensor. It is made strip of copper strip 1/2 inch wide, .003 inch thick, and around 5 3/8 inch long. Before cementing the blotting paper to the bottom of this copper strip, make sure to dry the blotting paper in an oven at 225 degrees F. for 15 minutes. After this drys, solder silver or tungsten contact on copper strip. Mount one side solid and horizontal and the free end will curl and move upward as bottom blotting paper absorbs moisture from the air. Blotting paper is not sized and made bulkier to provide capillary action for faster absorption of liquid. Good blotting paper has rag content to retain some strength after absorbing liquid. The sensor strip will move about 1/8 inch for every 10 % increase or decrease in moisture. The free of strip sensor end contacts screw with a lock nut to make an electrical circuit contact and allow for different humidity settings.
While shown as 6 volt battery in simulator, a charger to 6 volt D.C. connected to line voltage would be a simple and fast way to power the sensor circuit. Also, if automatic sensor is powered off, I have SPST switch below to allow manual ON/OFF control.
This sensor was mounted in small aluminum box that allowed good ventilation to sensor strip.
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