Hi,
I am looking at a project where I can monitor the presence of water in a sump.
I do not require the water level or the moisture content.
I would like to use a PCB as in:
My idea is to have the sensing PCB fitted to the bottom outside of a waterproof enclosure.
The device is to be battery powered and a single LED will come on if water is detected.
Is this feasible and could I use an ATTiny device for this (to read the sensor and control the LED)?
Many thanks
When you say "presence of water in a sump" I think "level switch", placed as low as possible, so a minimal level of water will trigger it.
Battery, resistor, level switch, LED. That's all you need. 1-2 cm of water is present; level switch closes the circuit; LED switches on. Water pumped out, level switch opens the circuit, LED switches off.
Thanks for your response.
I cannot use a level-switch.
I must be able to detect the presence of water with a depth of 1mm, or less.
That was my reasoning of using a capacitive-sensor.
Take a piece of wood put into nails they should be about a quarter inch away from each other connect 1 to 5 volt with a 300 Ohm resistor connect the other to an analog input pin there should be Infinity open loop when there's no water in the vessel as soon as the two electrodes share the same connection to any type of water the resistance should jump over $5,000 you should get a full closure you should get a reading and that could be as low as a fraction of a millimeter
the resistance should jump over $5,000
Wow!
Take a piece of wood put into nails
Are we still recovering from a good party?
I will never learn that my voice-to-text while driving gets me into trouble every time......
if you put your multi-meter into water, check the resistance. 5,000 ohms is not uncommon.
there are a lot of flood detectors, water leak detectors, water heater leak detectors.... that have two metal bits that are just above the floor. as soon as they both get wet, the circuit competes and
presto ! water alarm.
Wood could be a problem (when wet...)
"less than 1mm" could be a problem too (capillary action).
Leo..
Driving while surfing the Arduino forum is an extremely bad idea.
Please don't, and save someone's life.
Wawa:
Wood could be a problem (when wet...)
"less than 1mm" could be a problem too (capillary action).
Leo..
the 1mm would be spacing from the floor to the sensor. any water will have a rise of at least that.
also, the air gap will ensure there is no corrosion from the floor surface.
The idea was to have the OP make something today to prove concept.
I nice project box, with a a pair nuts and bolts, with a similar gap will last for decades.
Declan:
Thanks for your response.
I cannot use a level-switch.
I must be able to detect the presence of water with a depth of 1mm, or less.
That was my reasoning of using a capacitive-sensor.
You are assuming the water in question is a moderately good conductor (ie salty). A 1mm film
of pure water might be tricky to detect this way, especially through a thick plastic tank. I presume
the tank is plastic. I suspect a differential capacitive sensing circuit using some strips on a PCB
might work fairly well nonetheless, if the sump walls are thin enough compared to the water
depth. Water's dielectric constant is huge so its not hard to detect. If 1mm is a hard requirement
you may have problems.
dave-in-nj:
I will never learn that my voice-to-text while driving gets me into trouble every time......if you put your multi-meter into water, check the resistance. 5,000 ohms is not uncommon.
there are a lot of flood detectors, water leak detectors, water heater leak detectors.... that have two metal bits that are just above the floor. as soon as they both get wet, the circuit competes andpresto ! water alarm.
The conductivity of water varies over many orders of magnitude depending on dissolved salts, so
if you are in a soft water area the measurement could be very different from a hard water area.
A sprinkle of kitchen salt solves that easily 
Nevertheless, even at very soft water you'll be able to detect the difference between water and no water. Placing the two probes closer together and making them larger helps as well.
anyone have a multi-meter ?
it is not a hard test to put some tap water on a dish and touch probes to it.
if you are talking a basement flood sensor, you can take a piece of paper towel, dampen it
sprinkle some salt on it and let it dry
then place under the sensors.
as was noted, the effects rise in orders of magnitude, so instead of putting on just one grain of salt, one could give the salt shaker a good shake and put on a hundred.
Now, I have to go home, drain some of the distilled water from my HVAC condenser coil and test what resistance one drop has and what effect one grain of salt makes.......
