Water quality identification circuit

The quality of daily water directly affects people's health. Under amateur conditions, water quality identification cannot use professional
sampling, testing and analysis due to limited conditions. However, it is possible to directly detect the water through a self-made electronic device to visually display and judge the quality of the water, so it
is more practical. the value of.
    The detector circuit is shown in Figure 7-51. IC1 and peripheral components Ri, island, C, etc. form a multivibrator circuit. At the same time,
there is a water quality probe connected to the middle contact output terminal of R3 . The right side of the probe is connected to an LED "point" level display circuit composed of 1C2. Because the impurity content in water
is inversely proportional to its purity. When detecting water quality, if the water quality is good, it means that the impurity content
is low, and the concentration of hydrolyzed ions of the corresponding impurity components in the water is low, so the conductivity of the water is also low, the water resistance value is large, and the oscillation signal passes through the water. The amount of attenuation is correspondingly large. Therefore, the level
indicator appears on the "LED" display at a certain point in the range of "low" LED1~LED3 due to the low amplitude of the input signal. On the contrary, if the water quality is
poor and the amount of impurities is large, the oscillation signal will pass through the probe and be input to the LED display at a " high level " attenuation. As a result, the display appears on
the "LED" display at a certain point in the range of "high" LED4 ~ LED6.
    During actual production, a copper core sheathed wire with a diameter of 4mmz is used as the material, and a part of the insulating outer sheath is cut off with a knife at the lower part, so that
about 10mm of each copper wire core is exposed. Weld a pair of two-core shielded wires on the upper end (to prevent external clutter interference). thereafter. Wrap the connector with tape;
connect the other end of the screen wire to the measurement circuit. After
    the circuit is installed, simple calibration should be done: First, fill the cup with tap water as a test calibration source: place the probe in
the water in the cup, and press the power switch S while chanting. At this time, a certain LED in the indicator will light up, and then slowly adjust the adjustable resistor Rz,
so that the indicator point stays at the position of LED2 (green) while the lighting positions of LED1 to LED6 change. At this time, adjust the LED .