Water sense power-on circuit

Hi Guys!

I need some help with my Arduino project. I would like to create a small circuit that works underwater and display the water depth. The sensor and display part is done of the project but I get stuck with the on-off switch part.
Could somebody please help me with a decent circuit?
The basic idea the following: at "dry" conditions the circuit consumes zero power and when it gets submerged it will turn on my microcontroller. When the microcontroller finished the task it will turn off.
I would like to avoid the mechanical water switches.

Thanks!

fl11:
Hi Guys!

I need some help with my Arduino project. I would like to create a small circuit that works underwater and display the water depth. The sensor and display part is done of the project but I get stuck with the on-off switch part.
Could somebody please help me with a decent circuit?
The basic idea the following: at "dry" conditions the circuit consumes zero power and when it gets submerged it will turn on my microcontroller. When the microcontroller finished the task it will turn off.
I would like to avoid the mechanical water switches.

Thanks!

Do I understand this correctly? You are looking for a circuit that is not a switch, that consumes no power, but is able to switch power on to your Arduino? How will your circuit know when the Arduino has finished it's task? When will the power to your Arduino be turned off? Do you want the circuit to be able to repeat the sequence?
Paul

Hi Paul!

The logic of the circuit is like this: Latch or Self-power-off Arduino - Arduino Project Hub
With this "latching" method I can turn off my Arduino with code.
There is another great example for latching and self-power off GitHub - makermoekoe/Picoclick.
It will completely shut down the Arduino chip. I would like to use this method with water sensing power on ability.
And yes, I would like to repeat the sequence. If the circuit sense water again, it should turn on and start the logging, measuring.

Thanks!

How dry does your water sensing device have to be before it discovers there is no water? How much time do you think that will take?
Paul

If you really want zero power draw then you’re going to be limited to a mechanical switch of some sort. If you’re happy to accept a very small power draw then you can put the Arduino to sleep and wake it up occasionally to check an electronic sensor.

The classic rain detector/water sensor is the easiest to get working. You can either go with the Arduino version (google it, there’s thousands of tutorials) or the old analogue version that uses a few resistors and a single transistor. Either one can be made with a stupidly low current draw that will give you years of standby time using a few AA batteries. Make sure to use stainless steel sensing contacts to prevent corrosion and separate them by a reasonable distance so you don’t get water drops bridging the contacts when it’s taken out of the water.

Alternatively you could just use the pressure sensor you’re (presumably) already using. Water is heavy, if you measure much above normal atmospheric pressure then you must be under water.

I suggest looking up the Cave Pearl project as it deals with all this stuff.

Hi Again!

I’ve found a great circuit that may work for me.
Zero-power supply switch with water sense input

The circuit:


I’ve built this on my breadboard, it works fine with 10 volts. What is the best practice to modify the components that work at 3.3V? Sorry, but I’m a hobbyist in electronics, so I think I know the basics (what is npn, etc…) but the sizing and scaling the components are out of my scope.

Thanks!

Did you try that circuit at 3.3V ?
Try reducing all the resistor values to 3.3V/10V=0.33 % of their current value.

raschemmel:
3.3V/10V=0.33 % of their current value.

0.33, or 33%, not 0.33 %.

What he said...

What is the circuit's current draw? There's a good chance it will be higher than just putting the Arduino to sleep.

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