automatic water level circuit

Posted on Feb 4, 2014

Here we are using the Trigger and Threshold pins (2 & 6) to detect the maximum and minimum levels, respectively. The two voltage comparator op-amps inside the 555 control the output, turning it on/off. Looking at the circuit diagram you will notice that the Trigger` pin (2) is marked HIGH probe`, despite being triggered (output goes HIGH) when t

automatic water level circuit
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he voltage drops below 1/3 of the supply voltage and, the Threshold` pin (6) is marked LOW probe` while it is reset` (output goes LOW) when the voltage rises above 2/3 of the supply voltage. If this appears to you as being upside-down. One is the GROUND` probe, going to the level a little lower than the minimum desired level. This is the common` (or reference`) probe. The LOW and HIGH probes are set at the desired levels. Resistors R2 and R1 (1M) tie the Trigger` and Threshold` pins (2 & 6) to the positive (+) rail (supply). In other words, both pins are HIGH. Remember (from above), to make the output of IC1 go HIGH, the trigger pin (2) needs to drop below 1/3 of the supply voltage. (4V with a 12V supply) Since the trigger pin is still HIGH, the output remains LOW. Its purpose is phase reversal. It means that when IC1`s output is HIGH, TR1 conducts and pulls its collector/TR2`s GATE junction LOW, so TR2 is OFF. Since the pump (or relay coil) is connected between the positive rail (+12V) and TR2`s DRAIN, the pump/relay coil is NOT energized. Now, back to the condition when the IC1`s output is low, TR2`s GATE is HIGH (+12V) and conducting. The pump is operating and water is being filled. As the water level rises, a water bridge` is formed between the GROUND (common) probe and the LOW probe` (Threshold, pin 6) This bridge` constitutes a low resistance, relative to the high resistance of R2 (1M), bringing the voltage at this...

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