Water level automatic control circuit composed of NE555

As shown in the figure, this is an agricultural liquid level automatic control circuit. The control circuit consists of a step-down rectifier circuit, an RS trigger, a solid-state relay (SSR) control circuit, etc. The step-down rectifier circuit provides a DC voltage of VDD=+9V for the entire control circuit.

When there is no water in the pool, if the power is just turned on, the voltage on C3 cannot change suddenly, so the IC (555) pin ② is low, 555 is set, the high level output from pin 3 turns off the SSR, and the motor D does not run. At this time, C3 and C4 are charged through R1 and R2 respectively. When the voltage on C4 is charged to 2/3VDD, the IC is reset, and the low level output from pin ③ makes the photoelectric coupler inside the SSR connect the AC 220V voltage, and the motor D is powered to pump water. When the water level rises to probe b, C4 discharges through the water, but 555 still outputs a low level, and the motor D continues to rotate. When the water level rises to probe a, C3 discharges through the water. When C3 discharges to make the potential of pin ② lower than 1/3VDD, 555 is set, the high level output from pin 3 turns off the SSR, the motor D stops because of no electricity, and the liquid level begins to drop. When probe b emerges from the water, C4 is charged again, and the above process is repeated. This cycle repeats itself to keep the liquid level at a certain height.

SSR is an AC zero-crossing solid-state relay with a photoelectric coupler inside to isolate the control end from the output end, making it completely reliable.

In addition to automatically controlling the agricultural liquid level, the control circuit can also automatically control the water tower liquid level, etc.