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Aquarium water sensor and stray voltage

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skmdmasud

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Hi
I am planning to make a water sensor to detect the aquarium water has reached a marked point or not. What i am wondering is if there is stray voltage from some submerged 220VAC devices e.g heater will the stray voltage go to my uC through the ground plate to transistor and burn it.:nailbiting::nailbiting::nailbiting:

My Design
sch1.jpg
REGARDS.:angelic:
 

rumpfy

Active Member
Modern motor vehicles often have a fuel gauge AND a 'Low Level Fuel Warning Lamp'. This is because the fuel gauge is often not very accurate but a detector located at a low level part of the fuel tank will illuminate when the fuel level is low regardless of the fuel gauge reading.
The detection is done by using a Negative Temperature Coefficient resistor as a detector.
All you need is a DC supply and connect the NTC in series with a resistor (or lamp). When the NTC is cold by being in contact with the (fuel) water, the heat loss is great and the NTC cannot heat up so its resistance is high. When the (fuel)water level is low, then the NTC heats up and passes more current which is ultimately limited by the load (lamp or resistor). The usual set up in a vehicle is to use about a 2 watt globe and a 1300 ohm NTC. This is a simple arrangement but you could use a Wheatstone bridge arrangement to do the switching when the water level falls.
This kind of arrangement would keep DC power away from the water.
Another way you might do it is to use a float arrangement which blocks a light path between a LED and a photodiode. This stuff can often be scrounged from old photocopiers and the like.
Hope this helps.
 

skmdmasud

Member
Hi rumpfy
thanks for the methods. The first arrangement due to dipping there is a chance of leak current getting into the system. The float arrangement i think is a better choice i get full isolation, i saw float switches in the market a bit expensive cuz they switch 220VAC directly so i decided to make a simple float arrangement and some sort of mechanism which will simply push a switch costing almost nothing :D
 
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