Humidity indicator circuit composed of humidity detection amplifier and LED indication circuit

The humidity indicator circuit composed of a humidity detection amplifier and an LED indication circuit is as shown in the figure. RP uses organic solid potentiometers or variable resistors. By adjusting the resistance of RP, you can set the humidity value that requires warning. R1~R5 use 1/4W metal film resistors or carbon film resistors. RS is made with 3DG6 type transistors with values ​​greater than 100. When measuring, connect the black test lead of the multimeter to the C electrode and the red test lead to the forehead electrode. When you breathe into the transistor core with your mouth, the multimeter pointer should swing quickly to the right; when the water vapor on the tube core evaporates, the pointer of the multimeter can gradually move to the right. Swinging back to the left is normal.